BR122024004325A2 - DISPLAY DEVICES AND VIEWING ANGLE CONTROL OPTICAL ELEMENT FOR APPLICATION ON THE OUTPUT SIDE OF A DISPLAY DEVICE FOR USE IN AMBIENT LIGHTING - Google Patents

Abstract

This is a privacy visor comprising a polarized output spatial light modulator, reflective polarizer, multiple polar control retarders, and a polarizer. In a privacy mode of operation, on-axis light from the spatial modulator is directed without loss, while off-axis light is reduced in luminance. In addition, the reflectivity of the visor is reduced for on-axis reflections of ambient light, while reflectivity is increased for off-axis light. Visibility of the visor to on-axis onlookers is reduced by reducing luminance and increasing front reflectivity to ambient light. In a public mode of operation, the liquid crystal delay is adjusted so that off-axis luminance and reflectivity are not changed.

Description

FIELD OF TECHNIQUE

[0001] Divided from BR112020015167-0, filed on 01/24/2019.

[0002] This disclosure relates generally to illumination from light modulating devices, and more specifically to reflective optical stacks for use in a display, including a privacy display.

BACKGROUND

[0003] Privacy displays provide image visibility to a primary user who is typically at an on-axis position and reduced visibility of image content to an onlooker who is typically at an off-axis position. A privacy function may be provided by MicroLouvre optical films that transmit high luminance from a display in an on-axis direction with low luminance at off-axis positions, however, such films are not switchable and therefore the display is limited to the sole privacy function.

[0004] Switchable privacy visors may be provided by controlling the off-axis optical output.

[0005] Control may be provided by means of luminance reduction, for example by means of switchable backlights for a liquid crystal display (LCD) spatial light modulator (SLM). Display backlights generally employ waveguides and light sources disposed along at least one leading edge of the waveguide. Certain directional imaging backlights have the additional capability of directing illumination across a display panel to viewing windows. An imaging system may be formed between multiple sources and their respective window images. An example of a directional imaging backlight is an optical valve which may employ a folded optical system and therefore may also be an example of a folded imaging directional backlight. Light may propagate substantially without loss in one direction through the optical valve, while counter-propagating light may be extracted by reflection from inclined facets, as described in U.S. Pat. No. 9,519,153, which is incorporated herein by reference in its entirety.

[0006] Off-axis privacy control may further be provided by means of contrast reduction, for example by adjusting the slope of the liquid crystal bias in an in-plane switching LCD.

BRIEF SUMMARY

[0007] According to a first aspect of the present disclosure, there is provided a display device for use in ambient lighting, comprising: an SLM arranged to emit light; wherein the SLM comprises an output polarizer disposed on the output side of the SLM, the output polarizer being a linear polarizer; an additional polarizer disposed on the output side of the output polarizer, the additional polarizer being a linear polarizer; a reflective polarizer disposed between the output polarizer and the additional polarizer, the reflective polarizer being a linear polarizer; and at least one polar control retarder disposed between the reflective polarizer and the additional polarizer, wherein the at least one polar control retarder is capable of simultaneously introducing no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis along a line perpendicular to the plane of the at least one polar control retarder and introducing a relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder.

[0008] The at least one polar control retarder may be arranged to introduce no phase shift in the polarization components of light passed through the reflective polarizer along an axis along a line perpendicular to the plane of the at least one polar control retarder and/or to introduce a phase shift in the polarization components of light passed through the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder.

[0009] Advantageously, a directional display may be provided that provides high reflectivity and low luminance for off-axis viewing positions; and low reflectivity and high luminance for on-axis viewing positions. This increased reflectivity and reduced luminance provides enhanced privacy performance, including an increased visual safety level (VSL) for viewers off-axis of the display in an ambient lighting environment. A privacy display may have low image visibility to an off-axis onlooker viewing the display under ambient conditions. The on-axis viewer may observe a substantially unmodified display. A display with low stray light may have low image visibility to some viewers and high image visibility to other viewers. The display may be used in a motor vehicle to block visibility to passengers or drivers.

[0010] The at least one polar control retarder may comprise a switchable liquid crystal (LC) retarder comprising a layer of LC material, wherein the at least one polar control retarder may be arranged, in a switchable state of the switchable LC retarder, simultaneously to introduce no net relative phase shift for orthogonal polarization components of light passed by the reflective polarizer along an axis along a line perpendicular to the plane of the at least one polar control retarder and to introduce a net relative phase shift for orthogonal polarization components of light passed by the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder.

[0011] Advantageously, a display can be switched between a privacy or low-dispersion mode with high reflectivity and low luminance for an onlooker; and a wide-viewing-angle mode with increased luminance and reduced reflectivity for off-axis users, achieving high-contrast images for multiple users of the display. The primary user can view the display with substantially the same high luminance and low reflectivity in both modes of operation.

[0012] The at least one polar control retarder may further comprise at least one passive retarder which may be arranged to introduce no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis along a line perpendicular to the plane of the at least one passive retarder and to introduce a net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one passive retarder.

[0013] Advantageously, the polar region over which a high VSL can be achieved can be substantially increased compared to displays with a switchable LC polar control retarder and no passive polar control retarder.

[0014] Where the at least one polar control retarder comprises a switchable LC retarder, in an alternative, the switchable LC retarder may comprise two surface alignment layers disposed adjacent to the LC material on opposite sides thereof and each disposed to provide homeotropic alignment on the adjacent LC material. The LC material layer of the switchable LC retarder may comprise an LC material having a negative dielectric anisotropy. The LC material layer may have a retardance for light of a wavelength of 550 nm in a range of 500 nm to 1,000 nm, preferably in a range of 600 nm to 900 nm, and most preferably in a range of 700 nm to 850 nm.

[0015] When two surface alignment layers that provide homeotropic alignment are provided, the at least one polar control retarder may further comprise a passive retarder with an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardance for light of a wavelength of 550 nm in a range of -300 nm to -900 nm, preferably in a range of -450 nm to -800 nm, and most preferably in the range of -500 nm to -725 nm.

[0016] Alternatively, when two surface alignment layers are provided that provide homeotropic alignment, the at least one polar control retarder further comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the pair of passive retarders has a retardance for light of a wavelength of 550 nm in a range of 300 nm to 800 nm, preferably in a range of 500 nm to 700 nm, and most preferably in a range of 550 nm to 675 nm. Advantageously, in this case, high transmission and low reflectivity can be provided over a wide field of view without applied voltage. Furthermore, a narrow field of view can be provided in a lateral direction in a privacy mode of operation, with low power consumption.

[0017] Where the at least one polar control retarder comprises a switchable LC retarder, in another alternative, the switchable LC retarder may comprise two surface alignment layers disposed adjacent to the LC material layer and on opposite sides thereof and each disposed to provide homogeneous alignment in the adjacent LC material. Advantageously, compared to homeotropic alignment on opposite sides of the LC, greater resilience to LC material flow visibility during applied pressure may be achieved.

[0018] The LC material layer of the switchable LC retarder may comprise an LC material having a positive dielectric anisotropy. The LC material layer may have a retardance for light having a wavelength of 550 nm in a range of 500 nm to 900 nm, preferably in a range of 600 nm to 850 nm, and more preferably in a range of 700 nm to 800 nm.

[0019] When two surface alignment layers that provide homogeneous alignment are provided, the at least one polar control retarder may further comprise a passive retarder with an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardance for light of a wavelength of 550 nm in a range of -300 nm to -700 nm, preferably in a range of -350 nm to -600 nm, and most preferably in the range of -400 nm to -500 nm.

[0020] Alternatively, when two surface alignment layers providing homogeneous alignment are provided, the at least one polar control retarder may further comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the pair of passive retarders has a retardance for light of wavelength 550 nm in a range of 300 nm to 800 nm, preferably in a range of 350 nm to 650 nm, and most preferably in a range of 450 nm to 550 nm.

[0021] The field of view using a pair of passive retarders that have optical axes in the plane of the retarders that are crossed may have an enhanced luminance reduction and reflectivity increase in the privacy mode of operation.

[0022] When the at least one polar control retarder comprises a switchable LC retarder, in another alternative, the switchable LC retarder may comprise two surface alignment layers disposed adjacent to the LC material layer and on opposite sides, wherein one of the surface alignment layers is disposed to provide homeotropic alignment in the adjacent LC material and the other of the surface alignment layers is disposed to provide homogeneous alignment in the adjacent LC material.

[0023] When the surface alignment layer arranged to provide homogeneous alignment is between the LC material layer and the polar control retarder, the LC material layer may have a retardance for light with a wavelength of 550 nm in a range of 700 nm to 2,000 nm, preferably in a range of 1,000 nm to 1,500 nm, and more preferably from 1,200 nm to 1,500 nm.

[0024] When the surface alignment layer arranged to provide homogeneous alignment is between the LC material layer and the polar control retarder, the at least one polar control retarder may further comprise a passive retarder having its optical axis perpendicular to the plane of the retarder, wherein the at least one passive retarder has a retardance for light of wavelength 550 nm in a range of -400 nm to -1800 nm, preferably in a range of -700 nm to -1500 nm and more preferably in a range of -900 nm to -1300 nm.

[0025] When the surface alignment layer arranged to provide homogeneous alignment is between the LC material layer and the polar control retarder, the at least one polar control retarder may further comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each retarder of the pair of retarders has a retardance for light of wavelength 550 nm in a range of 400 nm to 1800 nm, preferably in a range of 700 nm to 1500 nm and most preferably in the range of 900 nm to 1300 nm. Advantageously, increased resilience to the visibility of LC material flow during applied pressure may be achieved.

[0026] When the surface alignment layer arranged to provide homeotropic alignment is between the LC material layer and the polar control retarder, the LC material layer may have a retardance for light with a wavelength of 550 nm in a range of 500 nm to 1800 nm, preferably in a range of 700 nm to 1500 nm, and most preferably in a range of 900 nm to 1350 nm.

[0027] When the surface alignment layer arranged to provide homeotropic alignment is between the LC material layer and the polar control retarder, the at least one polar control retarder may further comprise a passive retarder with its optical axis perpendicular to the plane of the retarder, wherein the at least one passive retarder has a retardance for light of wavelength 550 nm in a range of -300 nm to -1,600 nm, preferably in a range of -500 nm to -1,300 nm, and more preferably in a range of -700 nm to -1,150 nm.

[0028] When the surface alignment layer arranged to provide homeotropic alignment is between the LC material layer and the polar control retarder, the at least one polar control retarder may further comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each retarder of the pair of retarders has a retardance for light of wavelength 550 nm in a range of 400 nm to 1600 nm, preferably in a range of 600 nm to 1400 nm and most preferably in the range of 800 nm to 1300 nm. Advantageously, compared to homeotropic alignment on opposite sides of the LC, greater resilience to the visibility of LC material flow during applied pressure may be achieved.

[0029] Each alignment layer may have a pre-tilt that has a pre-tilt direction with a component in the plane of the LC material layer that is parallel, or antiparallel, or orthogonal to the electric vector transmission direction of the reflective polarizer. Advantageously high luminance may be achieved for front viewing positions.

[0030] Each alignment layer may have a pre-tilt that has a pre-tilt direction with a component in the plane of the LC material layer that is parallel, or antiparallel, or orthogonal to the electric vector transmission direction of the reflective polarizer.

[0031] When the at least one polar control retarder comprises a switchable LC retarder, the at least one passive retarder may further comprise two passive retarders, wherein the switchable LC retarder is provided between the two passive retarders. The display device may further comprise a transmissive electrode and an LC surface alignment layer formed on one side of each of the two passive retarders adjacent to the switchable LC retarder. The display device may further comprise first and second substrates between which the switchable LC retarder is provided, wherein the first and second substrates each comprise one of the two passive retarders. The two passive retarders may each comprise a passive retarder with an optical axis perpendicular to the plane of the retarder with a total retardance for light of wavelength 550 nm in a range of -300 nm to -700 nm, preferably in a range of -350 nm to -600 nm and more preferably in the range of -400 nm to -500 nm. Each of the two passive retarders may have an optical axis in the plane of the passive retarder, where the optical axes are crossed, and each passive retarder of the pair of passive retarders has a retardance for light of wavelength 550 nm in a range of 150 nm to 800 nm, preferably in a range of 200 nm to 700 nm and more preferably in the range of 250 nm to 600 nm. Advantageously the thickness, cost and complexity may be reduced.

[0032] The switchable LC retarder may further comprise transmissive electrodes arranged to apply a voltage to control the LC material layer. The transmissive electrodes may be on opposite sides of the LC material layer. The display device may further comprise a control system arranged to control the voltage applied across the electrodes of the switchable LC retarder. Advantageously, the display may be controlled to switch between privacy and public modes of operation.

[0033] The electrodes may be patterned to provide at least two pattern regions. Advantageously, a camouflage pattern may be applied in the privacy mode for luminance and reflectivity, and the front luminance and reflectivity may be substantially unchanged.

[0034] The at least one polar control retarder may comprise at least one passive retarder that is arranged to introduce no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis along a line perpendicular to the plane of the at least one passive retarder and to introduce a net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one passive retarder. Advantageously, thickness and cost may be reduced and efficiency may be increased if no switchable LC polar control retarder is provided.

[0035] The at least one polar control retarder may comprise at least one passive retarder. The at least one passive retarder may comprise at least two passive retarders with at least two different orientations of optical axes. Advantageously, a low cost privacy visor and a low stray light visor may be provided.

[0036] In an alternative, the at least one passive retarder may comprise a retarder with an optical axis perpendicular to the plane of the retarder. Advantageously, the thickness may be reduced.

[0037] In another alternative, the at least one passive retarder may comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed. Advantageously, the cost of the passive retarder may be reduced and high uniformity stretch films used for the passive retarder.

[0038] The retarder pair may have optical axes that extend 45° and 135°, respectively, relative to the electric vector transmission direction of the output polarizer.

[0039] The display device may further comprise an additional pair of passive retarders disposed between the first-mentioned pair of passive retarders and having optical axes in the plane of the passive retarders that are crossed. Advantageously, a privacy visor or low stray light visor may be provided for both landscape and portrait orientations. In an automotive vehicle, reflections from windshields and other glass surfaces may be reduced.

[0040] The additional pair of passive retarders may have optical axes that extend 0° and 90°, respectively, relative to an electric vector transmission direction that is parallel to the electric vector transmission of the output polarizer. Advantageously, a high VSL may be provided in polar regions with some rotational symmetry.

[0041] In another alternative, the at least one passive polar control retarder may comprise a retarder with an optical axis that is oriented with a component perpendicular to the plane of the retarder and a component in the plane of the retarder. The in-plane component of the passive retarder may extend at 0°, relative to an electrical vector transmission direction that is parallel or perpendicular to the electrical vector transmission of the display polarizer. The at least one passive polar control retarder may further comprise a passive retarder with an optical axis perpendicular to the plane of the passive retarder or a pair of passive retarders having optical axes in the plane of the passive retarders that are crossed.

[0042] Advantageously, a privacy visor may be provided that achieves luminance reduction and reflection enhancement in the lateral direction with low cost and complexity. A movable visor may be rotated about a horizontal axis while achieving comfortable image visibility for a primary user.

[0043] The display device may further comprise at least one other polar control retarder disposed between the output polarizer and the reflective polarizer. Advantageously, further modification of the field of view profile for transmitted light may be provided. The luminance may be reduced for an onlooker, while the primary user may observe substantially the same luminance.

[0044] The display device may further comprise a backlight arranged to emit light, wherein the SLM is a transmissive SLM arranged to receive light output from the backlight, wherein the backlight provides a luminance at polar angles to the line perpendicular to the SLM greater than 45 degrees that is at most 30% of the luminance along the line perpendicular to the SLM, preferably at most 20% of the luminance along the line perpendicular to the SLM, and most preferably at most 10% of the luminance along the line perpendicular to the SLM. Advantageously, a high VSL may be provided with low thickness and low cost. Furthermore, the VSL may be high in environments with reduced ambient lighting.

[0045] A further additional polarizer may be disposed between the further polar control retarder and the reflective polarizer. The display device may further comprise at least one further polar control retarder and a further additional polarizer, wherein the at least one further polar control retarder is disposed between the aforementioned further polarizer and the further additional polarizer. Advantageously, the luminance may be reduced to a dim.

[0046] The at least one further additional polar control retarder may comprise at least one further passive retarder. Advantageously, the increase in thickness and cost may be small.

[0047] The at least one first-mentioned polar control retarder may comprise a first switchable LC retarder comprising a first layer of LC material, and the at least one other polar control retarder may comprise a second switchable LC retarder comprising a second layer of LC material. The other switchable LC retarder may comprise at least one surface alignment layer disposed adjacent the LC material having a pre-tilt with a pre-tilt direction with an in-plane component of the LC material layer that is aligned parallel or antiparallel or orthogonal to the reflective polarizer.

[0048] Advantageously, the field of view in the public operating mode may be substantially unmodified, while other field of view profile modifications may be provided for the transmitted light in the privacy operating mode. Luminance may be reduced for an onlooker, while the primary user may observe substantially the same luminance. The first and second LC retarders may have different retardances. Chromatic variations with viewing angle may be reduced.

[0049] The electric vector transmission direction of the reflective polarizer may be parallel to the electric vector transmission direction of the additional polarizer and/or parallel to the electric vector transmission direction of the output polarizer.

[0050] The LC material layers of each of the first and second switchable LC retarders may have a retardance for light of wavelength 550 nm in a range of 450 nm to 850 nm, preferably in a range of 500 nm to 750 nm, and most preferably in a range of 550 nm to 650 nm. The VSL at high polar viewing angles may be increased.

[0051] The at least one first-mentioned polar control retarder further comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein the first of the pair of passive retarders has an optical axis that extends 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer, and the second of the pair of passive retarders has an optical axis that extends 135° relative to the electric vector transmission direction of the output polarizer; and the at least one other polar control retarder comprises a further pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein the first of the other pair of passive retarders has an optical axis that extends 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer; and the optical axes of one of the first-mentioned pair of passive retarders and of the other pair of passive retarders that are closest to each other extend in the same direction.

[0052] Advantageously, the color appearance of reflected and transmitted light to an off-axis viewer may be symmetrical for positive and negative side viewing angles. The minimum VSL may be increased.

[0053] Each passive retarder of the first-mentioned pair of passive retarders and each passive retarder of the other pair of passive retarders has a retardance for light of wavelength 550 nm in a range of 300 nm to 800 nm, preferably in a range of 350 nm to 650 nm and most preferably in a range of 400 nm to 550 nm. The VSL at high polar viewing angles may be increased.

[0054] The display device may further comprise: a backlight arranged to emit light, wherein the SLM is a transmissive SLM arranged to receive output light from the backlight, and the SLM further comprises an input polarizer arranged on the input side of the SLM, the input polarizer being a linear polarizer; and an additional polarizer arranged on the input side of the input polarizer, the additional polarizer being a linear polarizer; and at least one other polar control retarder is arranged between the additional polarizer and the input polarizer. Advantageously, the increase in thickness between the SLM and the display is reduced. Higher image fidelity may be provided and diffusion may be increased to reduce the appearance of specular reflections from the front surface to the front viewer. The number of lamination steps may be reduced and the VSL may be increased. A public mode may be provided with a wide viewing angle.

[0055] The display device may further comprise a control system arranged to control the application of a common voltage across the first and second switchable LC retarders, and wherein the LC material of the first LC retarder is different from the LC material of the second LC retarder. Advantageously, the cost of the control system may be reduced. Chromatic variations with viewing angle may be reduced.

[0056] The reflective polarizer and the output polarizer may have parallel electric vector transmission directions. The reflective polarizer and the additional polarizer may have parallel electric vector transmission directions. The reflective polarizer and the additional polarizer may have electric vector transmission directions that are not parallel, and the display device may further comprise a rotator retarder disposed between the reflective polarizer and the additional polarizer, the rotator retarder being arranged to rotate a polarization direction of polarized light incident thereon between the electric vector transmission directions of the display polarizer and the additional polarizer. Advantageously, high efficiency may be provided. The additional polarizer may be aligned with an electric vector transmission direction to transmit light through polarized sunglasses for typical user orientations. SLMs with non-parallel output electric vector transmission directions, such as TN-LCD, may be used.

[0057] According to a second aspect of the present disclosure, there is provided a viewing angle control optical element for application on the output side of a display device for use in ambient lighting comprising an SLM arranged to emit light; wherein the SLM comprises an output polarizer disposed on the output side of the SLM; wherein the viewing angle control optical element comprises an additional polarizer; a reflective polarizer disposed between the output polarizer and the additional polarizer in the application of the viewing angle control optical element to the display device; and at least one polar control retarder disposed between the reflective polarizer and the additional polarizer, wherein the at least one polar control retarder is capable of simultaneously introducing no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis along a line perpendicular to the plane of the at least one polar control retarder and introducing a relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder.

[0058] Advantageously, an aftermarket element can be attached to the displays by the display users. The element does not require complex alignment. Moiré beating between the element and the display pixels is not present and component selection with respect to pixel pitch is not necessary. Stock cost is reduced. Alternatively, the viewing angle control optical element can be conveniently factory-installed in the display modules.

[0059] The various features and alternatives defined above in relation to the first aspect of the present disclosure may be similarly applied to the second aspect of the present disclosure.

[0060] According to a third aspect of the present disclosure, there is provided a display device comprising: an SLM; a display polarizer disposed on at least one side of the SLM, the display polarizer being a linear polarizer; and a first additional polarizer disposed on the same side of the SLM as one of the at least one display polarizers, the first additional polarizer being a linear polarizer; and multiple first polar control retarders disposed between the first additional polarizer and the one of the at least one display polarizers; a further additional polarizer disposed on the same side of the SLM as said at least one of the at least one display polarizers, outside the first additional polarizer, the other additional polarizer being a linear polarizer; and multiple further polar control retarders disposed between the other first additional polarizer and the one of the at least one display polarizers another additional polarizer; wherein the first-mentioned multiple polar control retarders comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein the first of the pair of passive retarders has an optical axis that extends 45° relative to an electric vector transmission direction of the output polarizer, and the second of the pair of passive retarders has an optical axis that extends 135° relative to the electric vector transmission direction of the display polarizer that is an output polarizer and extends 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer, and wherein the other multiple polar control retarders comprise a further pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein the first of the pair of passive retarders has an optical axis that extends 135° relative to the electric vector transmission direction of the output polarizer and the second of the other pair of passive retarders has an optical axis that extends at 45° relative to the electric vector transmission direction of the display polarizer which is the output polarizer and extends at 45° and 135° respectively relative to an electric vector transmission direction of the output polarizer, and the optical axes of the one of the first pair of passive polar control retarders and the one of the other pair of passive polar control retarders that are closest to each other extend in the same direction.

[0061] Advantageously, a switchable privacy display may be provided with high image visibility over a wide field of view in a public operating mode. A wide-angle backlight may be provided, with reduced cost and increased robustness compared to collimated backlights. In a privacy operating mode, high VSLs may be achieved over a wide field of view in which an off-axis onlooker may be positioned, with low reflectivity of the display. Additional retarders and polarizers may be arranged between the backlight and the SLM so that surface-robust diffusers may be arranged on the front surface of the display to minimize visibility of front reflections while achieving high pixel fidelity. Chromaticity and luminance rolloffs may be symmetrical.

[0062] According to a fourth aspect of the present disclosure, there is provided a transmissive SLM arranged to receive output light from the backlight; an input polarizer arranged on the input side of the SLM and an output polarizer arranged on the output side of the SLM, the input polarizer and the output polarizer being linear polarizers; a first additional polarizer arranged on the output side of the output polarizer, the first additional polarizer being a linear polarizer; and first polar control retarders arranged between the first additional polarizer and the output polarizer; another additional polarizer arranged between the backlight and the input polarizer, the other additional polarizer being a linear polarizer; and further polar control retarders arranged between the first additional polarizer and the input polarizer; wherein the first polar control retarders comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, with respect to an electric vector transmission direction of the output polarizer, the other polar control retarders comprise another pair of passive retarders having optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively with respect to an electric vector transmission direction of the output polarizer, and the optical axes of the one of the first pair of passive polar control retarders and the one of the other pair of passive polar control retarders that are closest to each other extend in the same direction.

[0063] Advantageously, a switchable privacy display may be provided with high image visibility over a wide field of view in a public operating mode. A wide-angle backlight may be provided, with reduced cost and greater robustness compared to collimated backlights. In a privacy operating mode, high VSLs may be achieved over a wide field of view in which an off-axis onlooker may be positioned, with low reflectivity of the display. Some of the retarders and additional polarizers may be arranged between the backlight and the SLM so that surface-robust diffusers may be arranged on the front surface of the display to minimize the visibility of front reflections while achieving high pixel fidelity and high image contrast. Chromaticity and luminance rolloffs may be symmetrical. SLM dispersion may not affect the light that is transmitted through one of the retarders and additional polarizer, so that the VSL may be increased.

[0064] Embodiments of the present disclosure may be used in a variety of optical systems. Embodiments may include or work with a variety of projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, stand-alone projector systems, visual and/or audiovisual systems, and electrical and/or optical devices. Aspects of the present disclosure may be used with virtually any apparatus related to optical and electrical devices, optical systems, presentation systems, or any apparatus that may contain any type of optical system. Accordingly, embodiments of the present disclosure may be employed in optical systems, devices used in visual and/or optical presentations, visual peripherals, and so forth, and in various computing environments.

[0065] Before proceeding to the disclosed embodiments in detail, it should be understood that the disclosure is not limited in its application or creation to the details of the particular arrangements shown, because the disclosure has the capacity for other embodiments. Furthermore, aspects of the disclosure may be set forth in different combinations and arrangements to define unique embodiments in and of themselves. Furthermore, the terminology used herein is for purposes of description and not limitation.

[0066] These and other advantages and features of the present disclosure will become apparent to those skilled in the art after reading this disclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Embodiments are illustrated by way of example in the accompanying FIGURES, in which like reference numerals indicate like parts and in which:

[0068] FIGURE 1A is a diagram illustrating in perspective side view a switchable privacy visor for use in ambient lighting comprising a transmissive SLM, reflective polarizer, and compensated switchable retarder;

[0069] FIGURE 1B is a diagram illustrating in perspective side view a switchable privacy visor for use in ambient lighting comprising an emissive SLM and a compensated switchable retarder;

[0070] FIGURE 2A is a diagram illustrating in front view the alignment of optical layers in the optical stack of FIGURE 1A;

[0071] FIGURE 2B is a diagram illustrating in perspective side view a viewing angle control element comprising a reflective polarizer, a passive polar control retarder, a switchable LC retarder, and an additional polarizer;

[0072] FIGURE 3 is a diagram illustrating in perspective side view an arrangement of a switchable LC retarder comprising a passive negative polar control retarder on plate C in a privacy mode;

[0073] FIGURE 4A is a diagram illustrating in side view the propagation of output light from an SLM through the optical stack of FIGURE 1A in a privacy mode;

[0074] FIGURE 4B is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 4A;

[0075] FIGURE 5A is a diagram illustrating, in top view, the propagation of ambient illumination light through the optical stack of FIGURE 1A in a privacy mode;

[0076] FIGURE 5B is a graph illustrating the variation of reflectivity with polar direction for the reflected light rays in FIGURE 5A;

[0077] FIGURE 5C is a graph illustrating a measurement of the variation of reflectivity with lateral direction for the reflected light rays in FIGURE 5A;

[0078] FIGURE 6A is a diagram illustrating in front perspective view an observation of the output light transmitted to a display in privacy mode;

[0079] FIGURE 6B is a diagram illustrating in front perspective view an observation of ambient light reflected from interface surfaces of a display;

[0080] FIGURE 6C is a diagram illustrating in front perspective view an observation of ambient light reflected to the display of FIGURE 1A and FIGURE 1B in privacy mode;

[0081] FIGURE 7A is a diagram illustrating in front perspective views the appearance of the display of FIGURE 1A and FIGURE 1B in privacy mode;

[0082] FIGURE 7B is a graph illustrating the perceived dynamic range variation relative to ambient lighting for an off-axis onlooker of the switchable privacy visor of FIGURE 1A and FIGURE 1B in a privacy mode for arrangements with and without the reflective polarizer;

[0083] FIGURE 7C is a graph illustrating the variation of VSL with polar direction for a display of FIGURE 1A comprising a collimated backlight;

[0084] FIGURE 7D is a graph illustrating the variation of VSL with polar direction for a display that does not comprise multiple retarders;

[0085] FIGURE 8A is a diagram illustrating in side view a motor vehicle with a switchable directional display disposed within the vehicle cabin for entertainment and sharing modes;

[0086] FIGURE 8B is a diagram illustrating in top view a motor vehicle with a switchable directional display disposed within the cabin of the vehicle in an entertainment mode;

[0087] FIGURE 8C is a diagram illustrating in top view a motor vehicle with a switchable directional display disposed within the cabin of the vehicle in a sharing mode;

[0088] FIGURE 8D is a diagram illustrating in top view a motor vehicle having a switchable directional display disposed within the vehicle cabin for night and day modes;

[0089] FIGURE 8E is a diagram illustrating in side view a motor vehicle with a switchable directional display disposed within the cabin of the vehicle in night mode;

[0090] FIGURE 8F is a diagram illustrating in side view a motor vehicle with a switchable directional display disposed within the cabin of the vehicle in daytime mode;

[0091] FIGURE 9A is a diagram illustrating in perspective side view an arrangement of a switchable retarder in a public mode, wherein the switchable retarder comprises a switchable LC layer with homeotropic alignment and a passive C-plate polar control retarder;

[0092] FIGURE 9B is a diagram illustrating, in side view, the propagation of output light from an SLM through the optical stack of FIGURE 1A in a public mode;

[0093] FIGURE 9C is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 9B;

[0094] FIGURE 9D is a diagram illustrating in top view the propagation of ambient lighting light through the optical stack of FIGURE 1A in a public mode;

[0095] FIGURE 9E is a graph illustrating the variation of reflectivity with polar direction for light rays reflected in FIGURE 9D;

[0096] FIGURE 10A is a diagram illustrating in front perspective view the observation of output light transmitted to a display in public mode;

[0097] FIGURE 10B is a diagram illustrating in front perspective view the observation of reflected ambient light from the switchable display of FIGURE 1A in public mode;

[0098] FIGURE 10C is a diagram illustrating front perspective views of the appearance of the display of FIGURE 1A in public mode;

[0099] FIGURE 11A is a diagram illustrating in perspective side view an arrangement of a switchable retarder in a public mode, wherein the switchable retarder comprises a switchable LC layer with homogeneous alignment and cross-plate A polar control retarders;

[0100] FIGURE 11B is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 11A in a privacy mode;

[0101] FIGURE 11C is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 11A in a privacy mode;

[0102] FIGURE 11D is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 11A in a public mode;

[0103] FIGURE 11E is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 11A in a public mode;

[0104] FIGURE 11F is a diagram illustrating in perspective side view an arrangement of a privacy mode switchable compensated retarder comprising the passive cross-plate A polar control retarders and the homogeneously aligned switchable LC retarder, further comprising a passive rotation retarder;

[0105] FIGURE 12A is a diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode comprising a homogeneously aligned switchable LC retarder and a passive negative C plate retarder actuated with a first voltage;

[0106] FIGURE 12B is a diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode comprising a homogeneously aligned switchable LC retarder and a passive negative C plate retarder driven with a second voltage different from the first voltage;

[0107] FIGURE 12C is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 12A in a privacy mode;

[0108] FIGURE 12D is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 12A in a privacy mode;

[0109] FIGURE 12E is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 12B in a public mode;

[0110] FIGURE 12F is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 12B in a public mode;

[0111] FIGURE 13A is a diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode comprising a homogeneously aligned switchable LC retarder;

[0112] FIGURE 13B is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 13A in a privacy mode;

[0113] FIGURE 13C is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 13A in a privacy mode;

[0114] FIGURE 13D is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 13A in a public mode;

[0115] FIGURE 13E is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 13A in a public mode;

[0116] FIGURE 13F is a diagram illustrating in perspective side view a viewing angle control element comprising a reflective polarizer, a switchable LC retarder, and an additional polarizer;

[0117] FIGURE 14A is a diagram illustrating in perspective side view an arrangement of a privacy mode switchable retarder comprising passive cross-plate A retarders and a homeotropically aligned switchable LC retarder;

[0118] FIGURE 14B is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 14A in a privacy mode;

[0119] FIGURE 14C is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 14A in a privacy mode;

[0120] FIGURE 14D is a diagram illustrating in perspective side view an arrangement of a public mode switchable retarder comprising passive cross-plate A retarders and homeotropically aligned switchable LC retarder;

[0121] FIGURE 14E is a graph illustrating the variation of output luminance with polar direction for light rays transmitted in FIGURE 14D in a public mode;

[0122] FIGURE 14F is a graph illustrating the variation in reflectivity with polar direction for light rays reflected in FIGURE 14D in a privacy mode;

[0123] FIGURE 15A is a diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode comprising a homogeneously and homeotropically aligned switchable LC retarder and a passive negative C plate retarder;

[0124] FIGURE 15B is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 15A in a privacy mode;

[0125] FIGURE 15C is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 15A in a privacy mode;

[0126] FIGURE 15D is a graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 15A in a public mode;

[0127] FIGURE 15E is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 15A in a public mode;

[0128] FIGURE 16 is a diagram illustrating in side view a switchable privacy visor for use in ambient lighting comprising a non-collimating backlight, a passive retarder disposed between a reflective recirculating polarizer and a transmissive SLM, a reflective polarizer, a compensated switchable retarder, and additional polarizer;

[0129] FIGURE 17A is a diagram illustrating in perspective side view a switchable privacy visor for use in ambient lighting comprising an emissive SLM, a passive control retarder, a further additional polarizer, a reflective polarizer, a compensated switchable retarder, and a further polarizer;

[0130] FIGURE 17B is a diagram illustrating in perspective side view a viewing angle control element comprising a passive control retarder, a first additional polarizer, a reflective polarizer, a passive polar control retarder, a switchable LC retarder, and a second additional polarizer;

[0131] FIGURE 18A is a diagram illustrating in perspective side view a switchable privacy visor for use in ambient lighting comprising a wide-angle backlight, wherein multiple first retarders are disposed between the backlight and the SLM and multiple other retarders are disposed to receive light from the SLM;

[0132] FIGURE 18B is a diagram illustrating in front view the alignment of optical layers of an optical stack comprising multiple retarders disposed between a reflective polarizer and an additional polarizer and multiple other retarders disposed between the input polarizer and an additional polarizer of a transmissive SLM wherein multiple retarders and multiple other retarders each comprise crossed plates A;

[0133] FIGURE 18C is a graph illustrating the variation of logarithmic output luminance with polar direction for light rays transmitted from multiple retarders comprising crossed passive A plates and a homogeneously aligned switchable LC retarder;

[0134] FIGURE 18D is a graph illustrating in a lateral direction the variation of logarithmic output luminance with lateral viewing angle for light rays transmitted from multiple retarders comprising crossed passive A plates and a homogeneously aligned switchable LC retarder;

[0135] FIGURE 18E is a diagram illustrating in side view a switchable privacy visor for use in ambient lighting comprising an emissive SLM, a first compensated switchable LC retarder, a first additional polarizer, a reflective polarizer, a second compensated switchable LC retarder, and a second additional polarizer;

[0136] FIGURE 18F is a diagram illustrating in front view the alignment of optical layers of an optical stack comprising multiple retarders disposed between a reflective polarizer and an additional polarizer and multiple other retarders disposed between the output polarizer and another additional polarizer which is the reflective polarizer wherein the multiple retarders and multiple other retarders each comprise crossed plates A;

[0137] FIGURE 18G is a diagram illustrating in front view the alignment of optical layers of an optical stack comprising multiple retarders disposed between a further light absorbing polarizer and a further polarizer and multiple other retarders disposed between the output polarizer and the further polarizer wherein multiple retarders and multiple other retarders each comprise crossed plates A;

[0138] FIGURE 18H is a diagram illustrating in front view the alignment of optical layers of an optical stack for a transmissive SLM comprising multiple retarders disposed between a further light absorbing polarizer and a further polarizer and multiple other retarders disposed between the input polarizer and the further polarizer wherein the multiple retarders and multiple other retarders comprise crossed A plates;

[0139] FIGURE 18I is a diagram illustrating in front view the alignment of optical layers of an optical stack for a transmissive SLM comprising multiple retarders disposed between a further polarizer and the input polarizer of a transmissive SLM and multiple retarders disposed between the output polarizer and a further polarizer wherein the multiple retarders and multiple further retarders comprise crossed plates A;

[0140] FIGURE 18J is a diagram illustrating in perspective side view an arrangement of a privacy mode switchable retarder comprising a first negative C-plate passive retarder and the first homogeneously aligned switchable LC retarder disposed between the output polarizer and a reflective polarizer; and a second negative C-plate passive retarder and a second homogeneously aligned switchable LC retarder disposed between the reflective polarizer and an additional polarizer;

[0141] FIGURE 18K is a diagram illustrating in perspective side view a viewing angle control element comprising a first compensated switchable LC retarder, a first additional polarizer, a reflective polarizer, a second compensated switchable LC retarder, and a second additional polarizer;

[0142] FIGURE 19A is a diagram illustrating in top view a motor vehicle with a switchable directional display disposed within the vehicle cabin for daytime and/or sharing modes;

[0143] FIGURE 19B is a diagram illustrating in side view a motor vehicle with a switchable directional display disposed within the vehicle cabin for daytime and/or sharing modes;

[0144] FIGURE 19C is a diagram illustrating in top view a motor vehicle with a switchable directional display disposed within the vehicle cabin for night and/or entertainment modes;

[0145] FIGURE 19D is a diagram illustrating in side view a motor vehicle with a switchable directional display disposed within the vehicle cabin for night and/or entertainment modes;

[0146] FIGURE 20A is a diagram illustrating in perspective side view a privacy visor for use in ambient lighting comprising a backlight, a transmissive SLM, a reflective polarizer, a retarder stack, and an additional polarizer;

[0147] FIGURE 20B is a diagram illustrating in perspective side view a viewing angle control element comprising a reflective polarizer, a retarder stack, and an additional polarizer;

[0148] FIGURE 20C is a diagram illustrating in side perspective view a viewing angle control element comprising a first retarder stack and an additional polarizer; a reflective polarizer; a second retarder stack and another additional polarizer;

[0149] FIGURE 20D is a diagram illustrating in side perspective view a privacy visor for use in ambient lighting comprising a backlight, a reflective recirculating polarizer, an input retardant stack, a transmissive SLM, a reflective polarizer, a retardant stack, and an additional polarizer;

[0150] FIGURE 21A is a diagram illustrating in perspective side view an optical stack of a passive retarder comprising a negative C plate and arranged to provide modifications in the field of view of a display device;

[0151] FIGURE 21B is a graph illustrating the variation of output transmission with polar direction for light rays transmitted into the passive retarder of FIGURE 21A;

[0152] FIGURE 21C is a diagram illustrating in perspective side view an optical stack of a passive retarder comprising a negative plate O inclined in a plane orthogonal to the electric vector transmission direction of the display polarizer and a negative plate C and arranged to provide field of view modification of a display device;

[0153] FIGURE 21D is a graph illustrating the variation of output transmission with polar direction for light rays transmitted into the passive retarder of FIGURE 21C;

[0154] FIGURE 21E is a diagram illustrating in perspective side view an optical stack of a passive retarder comprising a positive plate O inclined in a plane orthogonal to the electric vector transmission direction of the display polarizer and crossed plates A arranged to provide a field of view modification of a display device;

[0155] FIGURE 21F is a graph illustrating the variation of output transmission with polar direction for light rays transmitted into the passive retarder of FIGURE 21E;

[0156] FIGURE 22A is a diagram illustrating in perspective side view an optical stack arranged to provide field of view modifications of a display device comprising two pairs of crossed plates A;

[0157] FIGURE 22B is a graph illustrating the variation of output transmission with polar direction for light rays transmitted into the passive retarder of FIGURE 22A;

[0158] FIGURE 23A and FIGURE 23B are diagrams illustrating in side view a privacy visor for use in ambient lighting comprising a transmissive SLM, a reflective polarizer, an LC retarder, compensating retarders, and an additional polarizer;

[0159] FIGURE 24A is a diagram illustrating in perspective side view an arrangement of a privacy mode switchable compensated retarder comprising a homogeneously aligned switchable LC retarder disposed between first and second C-plate passive polar control retarders;

[0160] FIGURE 24B and FIGURE 24C are graphs illustrating the variation of output transmission with polar direction for light rays transmitted in the optical stack of FIGURE 24A in a public mode and a privacy mode, respectively;

[0161] FIGURE 24D is a graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 24A in a privacy mode;

[0162] FIGURE 25A is a diagram illustrating in perspective side view a display comprising a switchable compensated retarder disposed between the first and second substrates of the passive polar control retarder of plate C;

[0163] FIGURE 25B is a diagram illustrating in side view part of a display comprising a switchable compensated retarder disposed between the first and second substrates of the passive polar control retarder of plate C;

[0164] FIGURE 25C is a diagram illustrating in side perspective view an arrangement of a public mode switchable compensated retarder comprising a homogeneously aligned switchable LC retarder disposed between the first and second passive cross polar control retarders of plate A;

[0165] FIGURE 25D and FIGURE 25E are graphs illustrating the variation of output transmission with polar direction for light rays transmitted to the array of FIGURE 25C in wide angle and privacy modes, respectively;

[0166] FIGURE 26A is a diagram illustrating in perspective side view an arrangement of a privacy mode switchable retarder comprising a negative C plate passive retarder and a homeotropically aligned switchable LC retarder further comprising a patterned electrode layer;

[0167] FIGURE 26B is a diagram illustrating in perspective view the illumination of the front view of a primary viewer and a looker through a camouflaged luminance controlled privacy visor;

[0168] FIGURE 26C is a diagram illustrating in perspective view the side illumination of an onlooker by a camouflaged luminance controlled privacy visor;

[0169] FIGURE 27A is a diagram illustrating in perspective side view an arrangement of a homogeneously aligned switchable LC retarder;

[0170] FIGURE 27B is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 27A for a first applied voltage;

[0171] FIGURE 27C is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 27A for a second applied voltage greater than the first applied voltage;

[0172] FIGURE 27D is a diagram illustrating in side perspective view a plate C disposed between parallel polarizers;

[0173] FIGURE 27E is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 27D;

[0174] FIGURE 28A is a diagram illustrating in perspective side view an arrangement of a homogeneously aligned switchable LC retarder disposed between parallel polarizers in series with a plate C disposed between parallel polarizers;

[0175] FIGURE 28B is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 28A for a first applied voltage;

[0176] FIGURE 28C is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 28A for a second applied voltage greater than the first applied voltage;

[0177] FIGURE 29A is a diagram illustrating in perspective side view an arrangement of a homogeneously aligned switchable LC retarder in series with a C-plate polar control retarder wherein the C-plate polar control retarder and the homogeneously aligned switchable LC are disposed between a single pair of parallel polarizers;

[0178] FIGURE 29B is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 29A for a first applied voltage;

[0179] FIGURE 29C is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 29A for a second applied voltage greater than the first applied voltage;

[0180] FIGURE 30A is a diagram illustrating in front perspective view a directional backlight;

[0181] FIGURE 30B is a diagram illustrating in front perspective view a non-directional backlight;

[0182] FIGURE 30C is a graph illustrating variation with luminance with side viewing angle of displays with different fields of view;

[0183] FIGURE 31A is a diagram illustrating in side view a switchable directional display apparatus comprising an imaging waveguide and a switchable LC retarder;

[0184] FIGURE 31B is a diagram illustrating in rear perspective view an operation of a narrow-angle mode imaging waveguide;

[0185] FIGURE 31C is a graph illustrating a field of view luminance plot of the output of FIGURE 31B when used in a display apparatus without a switchable LC retarder;

[0186] FIGURE 32A is a diagram illustrating in side view a switchable directional display apparatus comprising a switchable collimator waveguide and a switchable LC retarder in a privacy mode;

[0187] FIGURE 32B is a diagram illustrating in top view an output of a collimating waveguide;

[0188] FIGURE 32C is a graph illustrating a polar plot of isoluminance field of view for the display apparatus of FIGURE 32A;

[0189] FIGURE 33A is a diagram illustrating in perspective view the illumination of a retarder layer by off-axis light;

[0190] FIGURE 33B is a diagram illustrating in perspective view the illumination of a retarder layer by off-axis light from a first linear polarization state at 0 degrees;

[0191] FIGURE 33C is a diagram illustrating in perspective view the illumination of a retarder layer by off-axis light of a first 90 degree linear polarization state;

[0192] FIGURE 33D is a diagram illustrating in perspective view the illumination of a retarder layer by off-axis light of a first linear polarization state at 45 degrees;

[0193] FIGURE 34A is a diagram illustrating in perspective view the illumination of a plate retarder C by off-axis polarized light having a positive elevation;

[0194] FIGURE 34B is a diagram illustrating in perspective view the illumination of a plate retarder C by off-axis polarized light having a negative lateral angle;

[0195] FIGURE 34C is a diagram illustrating in perspective view the illumination of a plate retarder C by off-axis polarized light having a positive elevation and negative lateral angle;

[0196] FIGURE 34D is a diagram illustrating in perspective view the illumination of a plate retarder C by off-axis polarized light having a positive elevation and positive side angle;

[0197] FIGURE 34E is a graph illustrating the variation of output transmission with polar direction for the light rays transmitted in FIGURES 34A through 34D;

[0198] FIGURE 35A is a diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a positive elevation;

[0199] FIGURE 35B is a diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a negative lateral angle;

[0200] FIGURE 35C is a diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a positive elevation and negative side angle;

[0201] FIGURE 35D is a diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a positive elevation and positive side angle; and

[0202] FIGURE 35E is a graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURES 35A through 35D.

DETAILED DESCRIPTION

[0203] Terms related to optical retarders for the purposes of the present disclosure will now be described.

[0204] In a layer comprising a uniaxial birefringent material, there is a direction that governs the optical anisotropy, whereas all directions perpendicular to it (or at a certain angle to it) have equivalent birefringence.

[0205] The optical axis of an optical retarder refers to the direction of propagation of a light ray in uniaxial birefringent material in which no birefringence is experienced. This is distinct from the optical axis of an optical system which may, for example, be parallel to a line of symmetry or a line perpendicular to a display surface along which a principal ray propagates.

[0206] For light propagation in a direction orthogonal to the optic axis, the optic axis is the slow axis when linearly polarized light with an electric vector direction parallel to the slow axis travels at the lowest speed. The slow axis direction is the direction with the highest refractive index at the design wavelength. Similarly, the fast axis direction is the direction with the lowest refractive index at the design wavelength.

[0207] For positive dielectric anisotropic uniaxial birefringent materials, the slow axis direction is the extraordinary axis of the birefringent material. For negative dielectric anisotropic uniaxial birefringent materials, the fast axis direction is the extraordinary axis of the birefringent material.

[0208] The terms half wavelength and quarter wavelength refer to the operation of a retarder for a design wavelength Xo which may typically be between 500 nm and 570 nm. In the present illustrative embodiments, exemplary retardation values are provided for a wavelength of 550 nm unless otherwise specified.

[0209] The retarder provides a relative phase shift between two orthogonal polarization components of the light wave incident upon it and is characterized by the amount of relative phase, r, it imparts to the two polarization components. In some contexts, the term “phase shift” is used without the word “relative” but still means relative phase shift. The relative phase shift is related to the birefringence Δn and the thickness d of the retarder by:

[0210] In eq. 1, Δn is defined as the difference between the extraordinary and ordinary refractive index, i.e.,

[0211] For a half-wave retarder, the relationship between d, Δn, and ÀQ is chosen so that the phase shift between the polarization components is r = n. For a quarter-wave retarder, the relationship between d, Δn, and À0 is chosen so that the phase shift between the polarization components is r = n/2.

[0212] The term half-wave retarder in this document typically refers to the in-line light propagation perpendicular to the retarder and the in-line perpendicular spatial light modulator (SLM).

[0213] Some aspects of the propagation of light rays through a transparent retarder between a pair of polarizers will now be described.

[0214] The state of polarization (SOP) of a light ray is described by the relative amplitude and phase shift between any two orthogonal polarization components. Transparent retarders do not change the relative amplitudes of these orthogonal polarization components, but act only on their relative phase. Providing a net phase shift between the orthogonal polarization components changes the SOP, whereas maintaining the net relative phase preserves the SOP.

[0215] A linear SOP has a polarization component with nonzero amplitude and an orthogonal polarization component that has zero amplitude.

[0216] A linear polarizer transmits a single linear SOP that has a linear polarization component parallel to the electric vector transmission direction of the linear polarizer and attenuates light with a different SOP.

[0217] Absorbing polarizers are polarizers that absorb one polarization component of incident light and transmit a second orthogonal polarization component. Examples of absorptive linear polarizers are dichroic polarizers.

[0218] Reflective polarizers are polarizers that reflect one polarization component of incident light and transmit a second orthogonal polarization component. Examples of reflective polarizers that are linear polarizers are multilayer polymer film stacks such as 3M Corporation's DBEFTM or APFTM, or wire grid polarizers such as Moxtek's ProFluxTM. Reflective linear polarizers may further comprise cholesteric reflective materials and a fourth waveplate arranged in series.

[0219] A retarder disposed between a linear polarizer and a parallel linear analysis polarizer that introduces no relative net phase change provides complete transmission of light other than residual absorption within the linear polarizer.

[0220] A retarder that provides a relative net phase change between orthogonal polarization components alters the SOP and provides attenuation in the analysis polarizer.

[0221] In the present disclosure, an “A plate” refers to an optical retarder utilizing a layer of birefringent material with its optical axis parallel to the plane of the layer.

[0222] A “positive A-plate” refers to birefringent positive A-plates, i.e. A-plates with a positive Δn.

[0223] In the present disclosure, a “C-plate” refers to an optical retarder utilizing a layer of birefringent material with its optical axis perpendicular to the plane of the layer. A “positive C-plate” refers to a positively birefringent C-plate, i.e., a C-plate with a positive Δn. A “negative C-plate” refers to a negatively birefringent C-plate, i.e., a C-plate with a negative Δn.

[0224] “O plate” refers to an optical retarder that utilizes a layer of birefringent material with its optical axis having a component parallel to the plane of the layer and a component perpendicular to the plane of the layer. A “positive O plate” refers to positively birefringent O plates, i.e., O plates with a positive Δn.

[0225] Achromatic retarders may be provided wherein the retarder material has a retardance Δn.d that varies with wavelength Δ as

[0226] where K is substantially a constant.

[0227] Examples of suitable materials include modified polycarbonates from Teijin Films. Achromatic retarders may be provided in the present embodiments to advantageously minimize color shifts between polar angular viewing directions that have low luminance reduction and polar angular viewing directions that have increased luminance reductions, as will be described below.

[0228] Various other terms used in the present disclosure relating to retarders and liquid crystals will now be described.

[0229] A liquid crystal cell has a retardance given by Δn . d where Δn is the birefringence of the liquid crystal material in the liquid crystal cell and d is the thickness of the liquid crystal cell, independent of the alignment of the liquid crystal material in the liquid crystal cell.

[0230] Homogeneous alignment refers to the alignment of liquid crystals in switchable LCDs, where the molecules align substantially parallel to a substrate. Homogeneous alignment is sometimes called planar alignment. Homogeneous alignment can typically be provided with a small pre-tilt, such as 2 degrees, so that the molecules on the surfaces of the alignment layers of the liquid crystal cell are slightly tilted, as will be described below. The pre-tilt is arranged to minimize degeneracies in cell switching.

[0231] In the present disclosure, homeotropic alignment is the state in which rod-shaped liquid crystalline molecules align substantially perpendicular to the substrate. In discotic liquid crystals, homeotropic alignment is defined as the state in which a geometric axis of the column structure formed by disk-like liquid crystalline molecules aligns perpendicular to a surface. In homeotropic alignment, pre-tilt is the tilt angle of the molecules that are close to the alignment layer and is typically close to 90 degrees and, for example, can be 88 degrees.

[0232] In a twisted liquid crystal layer, a twisted configuration (also known as a helical structure or helix) of liquid crystal nematic molecules is provided. The twist can be achieved through a non-parallel alignment of alignment layers. Additionally, cholesteric dopants can be added to the liquid crystal material to stop the degeneracy of the twist direction (clockwise or counterclockwise) and to further control the twist pitch in the relaxed (typically indifferent) state. A super-twisted liquid crystal layer has a twist greater than 180 degrees. A twisted nematic layer used in SLMs typically has a twist of 90 degrees.

[0233] Liquid crystal molecules with positive dielectric anisotropy are switched from a homogeneous alignment (such as an A-plate retarder orientation) to a homeotropic alignment (such as a C- or O-plate retarder orientation) by an applied electric field.

[0234] Liquid crystal molecules with negative dielectric anisotropy are switched from a homeotropic alignment (such as a C or O plate retarder orientation) to a homogeneous alignment (such as an A plate retarder orientation) by an applied electric field.

[0235] Rod-like molecules have a positive birefringence, so that ne > no, as described in equation 2. Discotic molecules have negative birefringence, so that ne < no.

[0236] Positive retarders such as A-plates, positive O-plates, and positive C-plates can typically be provided by stretched films or rod-type liquid crystal molecules. Negative retarders, such as negative C-plates, can be provided by stretched films or discotic-type liquid crystal molecules.

[0237] Parallel alignment of liquid crystal cells refers to the alignment direction of homogeneous alignment layers being parallel or more typically antiparallel. In the case of pre-tilted homeotropic alignment, the alignment layers may have components that are substantially parallel or antiparallel. Hybrid aligned liquid crystal cells may have a homogeneous alignment layer and a homeotropic alignment layer. Twisted liquid crystal cells may be provided by alignment layers that do not have parallel alignment, e.g., oriented at 90 degrees to each other.

[0238] Transmissive SLMs may further comprise retarders between the input display polarizer and the output display polarizer, for example, as disclosed in U.S. Pat. No. 8,237,876 , which is incorporated herein by reference in its entirety. Such retarders (not shown) are in a different location than the passive retarders of the present embodiments. Such retarders compensate for contrast degradations for off-axis viewing locations, which is a different effect than the luminance reduction for off-axis viewing positions of the present embodiments.

[0239] A private mode of operation of a display is one in which an observer sees a low contrast sensitivity, such that an image is not clearly visible. Contrast sensitivity is a measure of the ability to discern between luminances of different levels in a static image. Inverse contrast sensitivity can be used as a measure of visual safety, since a high visual safety level (VSL) corresponds to low image visibility.

[0240] For a privacy display that provides an image to an observer, the visual security can be given as:

[0241] where VSL is the visual safety level, Y is the luminance of the white state of the display at a curious viewing angle, K is the luminance of the black state of the display at the curious viewing angle, and R is the luminance of the reflected light from the display.

[0242] The contrast ratio of the panel is given as:

[0243] For high contrast optical LCD modes, the white state transmission remains substantially constant with viewing angle. In the contrast-reducing liquid crystal modes of the present embodiments, the white state transmission typically reduces as the black state transmission increases so that

[0244] The visual safety level can be further provided as:

[0245] wherein the relative off-axis luminance, P, is typically defined as the percentage of frontal luminance, L, at the looking angle, and the display may have an image contrast ratio C, and the surface reflectivity is p.

[0246] The relative off-axis luminance, P, is sometimes referred to as the privacy level. However, this privacy level P describes the relative luminance of a display at a given polar angle compared to the frontal luminance and is not a measure of the appearance of privacy.

[0247] The display may be illuminated by Lambertian ambient illumination I. Thus, in a perfectly dark environment, a high contrast display has a VSL of approximately 1.0. As ambient illumination increases, the perceived image contrast decreases, the VSL increases, and a private image is perceived.

[0248] For typical liquid crystal displays, the panel contrast C is above 100:1 for almost all viewing angles, allowing the visual safety level to be approximated to:

[0249] Compared to privacy displays, desirable wide-angle displays are easily observed under standard ambient lighting conditions. A measure of image visibility is given by contrast sensitivity, such as Michelson contrast, which is given by:

[0250] and then:

[0251] Thus, the visual safety level (VSL) is equivalent to (but not identical to) 1/M. In the present discussion, for a given off-axis relative luminance, P, the wide-angle image visibility, W, is approximated as

[0252] Switchable directional display apparatuses for use in a privacy display, for example, and comprising multiple retarders disposed between a display polarizer and an additional polarizer, are described in U.S. Patent No. 10,126,575 and U.S. Patent Application No. 16/131,419, entitled “Optical stack for switchable directional display” (Attorney Dossier No. 412,101), filed September 14, 2018, both of which are incorporated herein by reference in their entirety. Directional display apparatuses further comprising reflective polarizers disposed between the polarizer and display retarders are described in U.S. Patent Publication No. 2018-0329,245, which is incorporated herein by reference in its entirety. Directional display polarizers comprising passive retarders disposed between a display polarizer and an additional polarizer are described in U.S. Patent Publication No. 2018-0321553, which is incorporated herein by reference in its entirety.

[0253] The structure and operation of various switchable display devices will now be described. In this description, common elements have common reference numerals. It should be noted that the disclosure relating to any element applies to each device in which the same or a corresponding element is provided. Accordingly, for the sake of brevity, such disclosure is not repeated.

[0254] FIGURE 1A is a schematic diagram illustrating in perspective side view an optical stack of a display device for use in ambient lighting; FIGURE 1B is a schematic diagram illustrating in perspective side view a switchable privacy display for use in ambient lighting comprising an emissive spatial light modulator (SLM) and compensated switchable retarder; and FIGURE 2A is a schematic diagram illustrating in front view the alignment of optical layers in the optical stack of FIGURE 1.

[0255] A display device 100 for use in ambient lighting 604 comprises: an SLM 48 arranged to emit light 400; wherein the SLM 48 comprises an output polarizer 218 disposed on the output side of the SLM 48, the output polarizer 218 being a linear polarizer; an additional polarizer 318 disposed on the output side of the output polarizer 218, the additional polarizer 318 being a linear polarizer; and a reflective polarizer 302 disposed between the output polarizer 218 and the additional polarizer 318, the reflective polarizer 302 being a linear polarizer. Typical polarizers 210, 218, 318 may be polarizers such as dichroic polarizers.

[0256] At least one polar control retarder 300 is disposed between the reflective polarizer 302 and the additional polarizer 318. The electric vector transmission direction 303 of the reflective polarizer 302 is parallel to the electric vector transmission direction 319 of the additional polarizer 318. The electric vector transmission direction 303 of the reflective polarizer 302 is parallel to the electric vector transmission direction 219 of the output polarizer 218.

[0257] Thus, a display device for use in ambient lighting 604 comprises an SLM 48 arranged to emit light 400. In the present disclosure, the SLM 48 may comprise a liquid crystal display comprising input polarizer 210, output polarizer 218 with substrates 212, 216, liquid crystal layer 214, and red, green, and blue pixels 220, 222, 224. Backlight 20 may be arranged to illuminate the SLM 48 and may comprise input light sources 15, waveguide 1, rear reflector 3, and optical stack 5 comprising diffusers, light shifting films, and other known optical backlight structures. Asymmetric diffusers, which may comprise asymmetric surface relief features, for example, may be provided in the optical stack 5 with greater diffusion in the elevation direction compared to the lateral direction. Advantageously, the uniformity of the image can be increased.

[0258] The structure and operation of the backlights 20 for use in a privacy display are further described with reference to FIGURES 30A through 32C below. In an illustrative embodiment of FIGURE 1A, the luminance at polar angles to the line perpendicular to the SLM greater than 45 degrees may be at most 18%.

[0259] The display may further comprise a reflective recirculating polarizer 208 disposed between the backlight 20 and the SLM 48. The reflective recirculating polarizer 208 is different from the reflective polarizer 302 of the present embodiments. The reflective recirculating polarizer 208 provides reflection of polarized light from the backlight having a polarization orthogonal to the electric vector transmission direction of the dichroic input polarizer 210. The reflective recirculating polarizer 208 does not reflect ambient light 604 to an onlooker.

[0260] As illustrated in FIGURE 1B, the SLM 48 may alternatively be provided by other types of displays that provide output light 400 by emission, such as organic LED (OLED) displays, with output polarizer 218. The output polarizer 218 may provide luminance reduction for light reflected from the OLED pixel plane via one or more retarders 518 inserted between the output display polarizer 218 and the OLED pixel plane. The one or more retarders 518 may be a quarter wave plate and is different from the retarder 330 of the present disclosure.

[0261] Thus, the SLM 48 comprises an output polarizer 218 disposed on the output side of the SLM 48. The output polarizer 218 may be arranged to provide a high extinction ratio for light from pixels 220, 222, 224 of the SLM 48 and to prevent back reflections from the reflective polarizer 302 toward the pixels 220, 222, 224.

[0262] Polar control retarder 300 is disposed between reflective polarizer 302 and additional polarizer 318. In the embodiment of FIGURES 1A-1B, polar control retarder 300 comprises passive polar control retarder 330 and switchable liquid crystal retarder 301, but in general it may be replaced by other configurations of at least one retarder, some examples of which are present in the devices described below.

[0263] The at least one polar control retarder 300 has the capability of simultaneously introducing no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer 302 along an axis along a line perpendicular to the plane of the at least one polar control retarder 300 and introducing a relative phase shift to orthogonal polarization components of light passed through the reflective polarizer 302 along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder 300. The polar control retarder 300 does not affect the luminance of light passing through the reflective polarizer 302, the polar control retarder 300, and the additional polarizer 318 along an axis along a line perpendicular to the plane of the polar control retarder 300, but the polar control retarder 300 reduces the luminance of light passing therethrough along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder 300. of the polar control retarder 300, at least in one of the switchable states of the switchable retarder 301. The principles leading to this effect are described in more detail below with reference to FIGURES 33A-35E and arise from the presence or absence of a phase shift introduced by the polar control retarder 300 to light along geometric axes that are angled differently relative to the liquid crystal material of the polar control retarder 300. A similar effect is achieved in all of the devices described below.

[0264] The polar control retarder 300 comprises a switchable liquid crystal retarder 301 comprising a layer 314 of liquid crystal material and substrates 312, 316 disposed between the reflective polarizer 302 and the additional polarizer 318. Thus, the at least one polar control retarder 300 comprises a switchable liquid crystal retarder 301 comprising a layer 314 of liquid crystal material 414, wherein the at least one polar control retarder 300 is disposed, in a switchable state of the switchable liquid crystal retarder 301, simultaneously to introduce no net relative phase shift to orthogonal polarization components of light passed by the reflective polarizer 302 along an axis along a line perpendicular to the plane of the at least one polar control retarder 300 and to introduce a net relative phase shift to orthogonal polarization components of light passed by the reflective polarizer 302 along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder.

[0265] As illustrated in FIGURE 2A, in the case where the SLM 48 is a liquid crystal display, the input electric vector transmission direction 211 in the input polarizer 210 provides an input polarization component that can be transformed by the liquid crystal layer 214 to provide the output polarization component determined by the electric vector transmission direction 219 of the output polarizer 218. The electric vector transmission direction of the reflective polarizer 302 is parallel to the electric vector transmission direction of the output polarizer 218. Furthermore, the electric vector transmission direction 303 of the reflective polarizer 302 is parallel to the electric vector transmission direction 319 of the additional polarizer 318.

[0266] The substrates 312, 316 illustrated in FIGURE 1A of the switchable liquid crystal retarder 301 comprise electrodes 413, 415 (illustrated in FIGURE 3) arranged to provide a voltage across the layer 314 of the liquid crystal material 414. The control system 352 is arranged to control the voltage applied by the voltage driver 350 across the electrodes of the switchable liquid crystal retarder 301.

[0267] The polar control retarder 300 further comprises a passive polar control retarder 330, as will be described later. The at least one polar control retarder 300 comprises at least one passive retarder 330 that is arranged to introduce no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer 302 along an axis along a line perpendicular to the plane of the at least one passive retarder and to introduce a net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer 302 along an axis inclined to a line perpendicular to the plane of the at least one passive retarder.

[0268] The passive polar control retarder 330 may comprise a retarder layer of a solid birefringent material 430, while the switchable liquid crystal retarder 301 may comprise a layer 314 of liquid crystal material 414, as will be described below.

[0269] FIGURE 2B is a schematic diagram illustrating in perspective side view a viewing angle control element 260 comprising a reflective polarizer 302; a polar control retarder 300 comprising a passive polar control retarder 330, a switchable liquid crystal retarder 301; and an additional polarizer. Features of the arrangement of FIGURE 2B not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0270] The viewing angle control optical element 260 is for application on the output side of a display device for use in ambient lighting 604 comprising an SLM 48 arranged to emit light; wherein the SLM 48 comprises an output polarizer 218 disposed on the output side of the SLM 48; wherein the viewing angle control optical element 260 comprises an additional polarizer 318; a reflective polarizer 302 disposed between the output polarizer 218 and the additional polarizer 318 in applying the viewing angle control optical element 260 to the display device; and at least one polar control retarder 300 disposed between the reflective polarizer 302 and the additional polarizer 318; wherein the at least one polar control retarder 300 has the capability of simultaneously introducing no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer 302 along an axis along a line perpendicular to the plane of the at least one polar control retarder 300 and introducing a relative phase shift to the orthogonal polarization components of light passed through the reflective polarizer 302 along an axis inclined to a line perpendicular to the plane of the at least one polar control retarder.

[0271] In use, the viewing angle control optical element 260 may be attached by a user or may be factory fitted to a polarized output SLM 48. The viewing angle control optical element 260 may be provided on a flexible film for curved and folded displays. Alternatively, the viewing angle control optical element 260 may be provided on a rigid substrate, such as a glass substrate.

[0272] Advantageously, an after-market privacy control element and/or stray light control element may be provided that does not require matching to the pixel resolution of the panel to avoid Moiré artifacts. The 260° viewing angle control optical element may further be provided for factory fit to the SLM 48.

[0273] By connecting the viewing angle control optical element 260 of FIGURE 2B to an existing display device, it is possible to form a display device as shown in any of FIGURES 1A through 2A.

[0274] The arrangement and operation of the polar control retarder 300 comprising a switchable liquid crystal retarder 301 will now be discussed.

[0275] FIGURE 3 is a schematic diagram illustrating in perspective side view an arrangement of polar control retarder 300 in a privacy mode of operation comprising a C-plate negative passive polar control retarder 330 and a homeotropically aligned switchable liquid crystal retarder 301 in a privacy mode of operation.

[0276] In FIGURE 3 and other schematic diagrams below, some layers of the optical stack are omitted for clarity. For example, switchable liquid crystal retarder 301 is shown omitting substrates 312, 316. Features of the array of FIGURE 3 not discussed in more detail can be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0277] The switchable liquid crystal retarder 301 comprises a layer 314 of liquid crystal material 414 having a negative dielectric anisotropy. The passive polar control retarder 330 comprises a negative plate C with an optical axis perpendicular to the plane of the retarder 330, illustrated schematically by the orientation of the discotic material 430.

[0278] The liquid crystal retarder 301 further comprises transmissive electrodes 413, 415 arranged to control the liquid crystal material, the layer of liquid crystal material being switchable by adjusting the voltage applied to the electrodes. The electrodes 413, 415 may be along the layer 314 and are arranged to apply a voltage to control the liquid crystal retarder 301. The transmissive electrodes are on opposite sides of the layer of liquid crystal material 414 and may, for example, be ITO electrodes.

[0279] Alignment layers may be formed between electrodes 413, 415 and the liquid crystal material 414 of layer 314. The orientation of the liquid crystal molecules in the x-y plane is determined by the pre-tilt direction of the alignment layers such that each alignment layer has a pre-tilt wherein the pre-tilt of each alignment layer has a pre-tilt direction with a component 417a, 417b in the plane of layer 314 that is parallel or antiparallel or orthogonal to the electric vector transmission direction 303 of reflective polarizer 302.

[0280] The driver 350 supplies a voltage V to the electrodes 413, 415 along the layer 314 of the switchable liquid crystal material 414, such that the liquid crystal molecules are tilted at an angle of inclination to the vertical, forming a plate O. The plane of the inclination is determined by the pre-tilting direction of the alignment layers formed on the inner surfaces of the substrates 312, 316.

[0281] In typical use for switching between a public mode and a privacy mode, the liquid crystal material layer is switchable between two states, the first state being a public mode so that the display can be used by multiple users, and the second state being a privacy mode for use by a primary user with minimal visibility to onlookers. Switching may be by means of a voltage being applied across the electrodes.

[0282] In general, such a display may be considered to have a first wide-angle state and a second reduced off-axis luminance state. Such a display may provide a privacy visor. In another use or to provide controlled luminance to off-axis observers, for example in an automotive environment, when a passenger or driver may desire some visibility of the displayed image, without total obscuration, through intermediate voltage levels. Stray light may be reduced for nighttime operation.

[0283] Polarized light propagation from output polarizer 218 will now be considered for both on-axis and off-axis directions.

[0284] FIGURE 4A is a schematic diagram illustrating in side view the propagation of output light from an SLM through the optical stack of FIGURE 1A in a privacy mode of operation; and FIGURE 4B is a schematic graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 4A. When the liquid crystal material layer 314 is in a second state of said two states, the polar control retarder 300 does not provide overall transformation of the polarization component 360 to emit light rays 400 passing therethrough along an axis perpendicular to the plane of the switchable retarder, but provides overall transformation of the polarization component 361 into light rays 402 passing therethrough for some polar angles that are at an acute angle to the perpendicular to the plane of the retarders. Features of the arrangement of FIGURE 4A not discussed in further detail may be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0285] The polarization component 360 of the output polarizer 218 is transmitted by the reflective polarizer 302 and incident on the retarders 300. On-axis light has a polarization component 362 that is unchanged from the component 360, while off-axis light has a polarization component 364 that is transformed by the polar control retarder 300. At a minimum, the polarization component 361 is transformed to a linear polarization component 364 and absorbed by the additional polarizer 318. More generally, the polarization component 361 is transformed to an elliptical polarization component, which is partially absorbed by the additional polarizer 318.

[0286] Thus, in a polar representation of transmission by polar control retarder 300 and additional polarizer 318 in a privacy mode, high transmission regions and low transmission regions are provided as illustrated in FIGURE 4B.

[0287] The polar distribution of light transmission illustrated in FIGURE 4B modifies the polar distribution of luminance output from the underlying SLM 48. In the case where the SLM 48 comprises a directional backlight 20, the off-axis luminance may be further reduced as described above.

[0288] Advantageously, a privacy visor is provided with low luminance for an onlooker off-axis while maintaining high luminance for an on-axis observer.

[0289] The operation of reflective polarizer 302 for light from ambient light source 604 will now be described.

[0290] FIGURE 5A is a schematic diagram illustrating in top view the propagation of ambient illumination light through the optical stack of FIGURE 1A in a privacy mode of operation; and FIGURE 5B is a schematic graph illustrating the variation of reflectivity with polar direction for reflected light rays in FIGURE 5A. Features of the arrangement of FIGURE 5A not discussed in further detail may be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0291] The ambient light source 604 illuminates the display 100 with unpolarized light. The additional polarizer 318 transmits the light ray 410 in a line perpendicular to the display surface with a first polarization component 372 that is a linear polarization component parallel to the electric vector transmission direction 319 of the additional polarizer 318.

[0292] In both operating states, the polarization component 372 remains unmodified by the polar control retarder 300, and therefore the transmitted polarization component 382 is parallel to the transmission axis of the reflective polarizer 302 and the output polarizer 218, so that ambient light is directed through the SLM 48 and lost.

[0293] In comparison, for beam 412, off-axis light is directed through polar control retarder 300 so that polarization component 374 incident on reflective polarizer 302 can be reflected. This polarization component is reconverted to component 376 after passing through retarders 300 and is transmitted through additional polarizer 318.

[0294] Thus, when the liquid crystal material layer 314 is in the second state of said two states, the reflective polarizer 302 does not provide reflected light to the ambient light rays 410 passing through the additional polarizer 318 and then the polar control retarder 300 along an axis perpendicular to the plane of the polar control retarder 300, but provides reflected light rays 412 to the ambient light passing through the additional polarizer 318 and then the polar control retarder 300 at some polar angles that are at an acute angle to the perpendicular to the plane of the polar control retarder 300; wherein the reflected light 412 passes back through the polar control retarder 300 and is then transmitted by the additional polarizer 318.

[0295] The polar control retarder 300 therefore does not provide overall transformation of the polarization component 380 in ambient light rays 410 passing through the additional polarizer 318 and then the polar control retarder 300 along an axis perpendicular to the plane of the switchable retarder, but rather provides an overall transformation of polarization component 372 for the ambient light rays 412 passing through the absorption polarizer 318 and then the polar control retarder 300 at some polar angles that are at an acute angle to the perpendicular to the plane of the polar control retarder 300.

[0296] The polar distribution of light reflection illustrated in FIGURE 5B therefore illustrates that high reflectivity can be provided in typical onlooker locations via the privacy state of the polar control retarder 300. Thus, in the privacy mode of operation, reflectivity for off-axis viewing positions is increased and luminance for off-axis light from the SLM is reduced as illustrated in FIGURE 4B.

[0297] Advantageously, a privacy visor is provided with high reflectivity to an off-axis onlooker while maintaining low reflectivity to an on-axis observer. As described above, this increased reflectivity provides an increased level of visual safety for the visor in a bright environment.

[0298] In another application, such a display may provide a switchable mirror appearance. Such a display may improve the aesthetic appearance of displays that are not in operation. For example, in a television application in a home environment, the display may be provided with a mirror for off-axis viewing, hiding the “black hole” typical of large area televisions by reflecting ambient light, advantageously providing perceived expansion of the living area.

[0299] The reflectivity measurements of the arrangement of FIGURE 5A will now be described.

[0300] FIGURE 5C is a schematic graph illustrating a measurement of the variation of reflectivity 390 with side viewing angle 392 for some reflected light rays 412. Profile 394 illustrates the variation of reflectivity for a display in privacy mode, while profile 396 illustrates the variation of reflectivity for a display in public mode.

[0301] In comparison to FIGURE 5B, the peak reflectivity is approximately 20%, where 50% represents the reflectivity of a perfect reflective polarizer 302. This reduced reflectivity is due to transmission losses of the additional polarizer 318, polarization reflection efficiency of the reflective polarizer, chromatic drift of the set point for the polar control retarder 300, and other reflection and scattering losses within the optical stack.

[0302] The operation of the privacy mode of the display of FIGURE 1A will now be further described.

[0303] FIGURE 6A is a schematic diagram illustrating in front perspective view an observation of output light transmitted to a display operating in privacy mode. The display 100 may be provided with white regions 603 and black regions 601. An observer may observe an image on the display if a difference in luminance is detected between the observed regions 601, 603. In operation, the primary user 45 observes full luminance images by beams 400 to viewing locations 26 which may be optical windows of a directional display. The observer 47 observes reduced luminance beams 402 at viewing locations 27 which may, for example, be optical windows of a directional display comprising an imaging waveguide. Regions 26, 27 further represent on-axis and off-axis regions of polar graphs 4B and 5B.

[0304] FIGURE 6B is a schematic diagram illustrating in front perspective view an observation of ambient light reflected from interface surfaces of a display. Thus, some of the light rays 404 illustrated in FIGURE 5A may be reflected by the front surface of the additional polarizer 318 and other surfaces of the display. Typically, this reflectivity may be 4% for an optical stack connected at perpendicular incidence and approximately 5% for an optical stack connected at 45 degree incidence, due to Fresnel reflections at the polarizer-air interface. Thus, a low luminance reflected image 605 from source 604 may be observed by the onlooker in front of display 100.

[0305] FIGURE 6C is a schematic diagram illustrating in front perspective view an observation of reflected ambient light for the display of FIGURE 1A operating in privacy mode. By way of comparison with FIGURE 6B, a substantially higher reflected luminance is observable from reflection 606 of source 604. The array features of FIGURES 6A-6C not discussed in further detail can be assumed to correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0306] The shape and distribution of the reflected image 606 are determined by the spatial distribution of the ambient light source 604, but may be further determined by diffusion layers, particularly at the output surface of the additional polarizer 318.

[0307] FIGURE 7A is a schematic diagram illustrating in front view the appearance of the display of FIGURE 1A operating in privacy mode 1 with variations in luminance and reflectivity as illustrated in FIGURE 4B and FIGURE 5B from different viewing positions. Thus, each of the nine views 520, 522, 524, 526, 528, 530, 532, 534, and 536 corresponds to a view from the corresponding viewing position, as shown by the perspectives of these views.

[0308] Thus, the upper viewing quadrant views 530, 532, lower viewing quadrant views 534, 536, and side viewing position views 526, 528 provide both reduced luminance and increased reflections 606, 605 from the ambient light source 604, whereas the views from the central upward and downward viewing regions 522, 524 and the front view 520 provide a region of much greater luminance and low reflectivity 605, with substantially no visibility of the reflection from the reflective polarizer 302.

[0309] FIGURE 7B is a schematic graph illustrating the variation of the Visual Safety Level 620 with respect to the ratio 622 of ambient illumination and frontal luminance for an off-axis onlooker of the switchable privacy visor of FIGURE 1A in a privacy mode of operation for profile arrangements 624 with reflective polarizer 302 and for profile 626 without reflective polarizer 302 and for the illustrative embodiment of TABLE 1. TABLE 1

[0310] FIGURE 7B thus illustrates that the level of visual safety is advantageously increased by the reflective polarizer 302.

[0311] In comparison to the present embodiments, the omission of the reflective polarizer 302 provides a visual safety level, V, that is less than 4.0 for typical ambient lighting. Such visual safety levels do not achieve desirable privacy for onlooker 27. The present embodiments achieve high visual safety levels above 4.0 for a lux/nit ratio of 20% or less. For example, desirable visual safety may be achieved for a front-facing user 26 viewing a 200 nit image in an environment with 40 nit ambient lighting. As ambient lighting increases, the visual safety level increases.

[0312] FIGURE 7C is a schematic graph illustrating the variation of visual safety level with polar direction for a display of FIGURE 1A comprising a collimated backlight 20 as will be described later with respect to FIGURES 32A through 32C and an ambient illumination (lux) to front luminance (nits) ratio (lux/nit) of 20%.

[0313] FIGURE 7C illustrates a first polar region 690 for viewing by the primary user 26, wherein a visual safety level, V, of less than 1.2 is achieved, providing image visibility, W, of greater than 83%. Advantageously, the display 100 can be conveniently viewed with high contrast. In a second polar region 692, the visual safety level, V, is greater than 4.0 and the eye of an onlooker positioned in that region will not be able to easily discern the information on the display. Polar region 694 is intermediate to regions 690 and 692 and is a region of reduced image visibility, although not at desirable levels of visual safety. Advantageously, the present embodiments achieve a large polar region 690 for the primary user and a large polar region 692 for the onlooker and a small transition region 694.

[0314] FIGURE 7D is a schematic graph illustrating the variation of visual safety level with polar direction for a display not comprising multiple retarders for the same lux/nit ratio as FIGURE 7C. Compared to the present embodiments, the polar region 692 of desirable visual safety level V > 4 is significantly reduced and the polar region 694 of reduced image visibility but insufficient visual safety level is increased.

[0315] By way of comparison with the present disclosure, single retarders that provide high reflectivity over a narrow angular range (such as typical “bullseye” patterns of single retarder layers and described, e.g., with reference to FIGURES 27A and 27B) do not achieve high reflectivity over a wide angular range. In particular, the double passage of reflected light illustrated in FIGURE 5A provides a very narrow region of high reflectivity. The reflected light must pass through the retarder twice, with the directions of the incoming and outgoing rays reversed relative to the perpendicular line of the display. This multiplies the optical effect and limits high reflectivity to rays with elevation angles close to the design angle (e.g., +/- 45 degrees side angle and zero degrees elevation). The underlying extended privacy performance around the horizontal of the present embodiments produces much larger regions of high visual security, e.g., polar region 692.

[0316] The present multiple retarders of the present embodiments provide high reflectivity over a wide angular range and achieve desirable privacy for an off-axis onlooker. Furthermore, the present retarders can be switched to provide low reflectivity and high image visibility in a public operating mode. Advantageously, the multiple retarders achieve significantly increased polar region 692 and significantly reduced polar region 694 while achieving comfortable image visibility for the primary user in polar region 690.

[0317] It may be desirable to provide controllable display illumination in an automotive vehicle.

[0318] FIGURE 8A is a schematic diagram illustrating in side view a motor vehicle with a switchable directional display 100 disposed within the vehicle cabin 602 of a motor vehicle 600 for both entertainment and sharing modes of operation. The light cone 610 (e.g., representing the light cone within which the luminance is greater than 50% of the peak luminance) may be provided by the luminance distribution of the display 100 in the elevation direction and is not switchable. Additional display reflectivity may be increased compared to the frontal reflectivity outside of this light cone 610.

[0319] FIGURE 8B is a schematic diagram illustrating in top view a motor vehicle with a switchable directional display 100 disposed within the vehicle cabin 602 in an entertainment mode of operation and operates in a manner similar to a privacy visor. The light cone 612 is provided with a narrow angular range so that the passenger 606 can see the display 100 while the driver 604 may not see an image on the display 100 as a result of the reduced luminance and increased reflectivity. Advantageously, entertainment images may be displayed to the passenger 606 without distraction to the driver 604.

[0320] FIGURE 8C is a schematic diagram illustrating in top view a motor vehicle with a switchable directional display 100 disposed within the vehicle cabin 602 in a sharing mode of operation. The light cone 614 is provided with a wide angular range so that all occupants can perceive an image on the display 100, for example, when the display is not moving or when non-distracting images are provided.

[0321] FIGURE 8D is a schematic diagram illustrating in top view a motor vehicle with a switchable directional display 100 disposed within vehicle cabin 602 for nighttime and daytime operating modes. In comparison to the arrangements of FIGURES 7C-7E, the optical output is rotated such that the elevation direction of the display is along an axis between the locations of driver 604 and passenger 606. Light cone 620 illuminates driver 604 and passenger 606 and with low reflectivity of the display.

[0322] FIGURE 8E is a schematic diagram illustrating in side view a motor vehicle with a switchable directional display 100 disposed within the vehicle cabin 602 in a nighttime operating mode. Thus, the display may provide a narrow angular output cone of light 622. Stray light that illuminates interior surfaces and occupants of the vehicle cabin 602 and causes distraction to the driver 604 may advantageously be substantially reduced. The driver 604 and passenger 606 may advantageously be able to observe the displayed images.

[0323] FIGURE 8F is a schematic diagram illustrating in side view a motor vehicle with a switchable directional display 100 disposed within the vehicle cabin 602 in a daytime operating mode. Thus, the display may provide a narrow angular output cone of light 624. Advantageously, the display may be conveniently observed by all occupants of the cabin 602.

[0324] The displays 100 of FIGURES 8A through 8F may be arranged in other locations within the vehicle cabin, such as driver instrument displays, center console displays, and seatback displays.

[0325] The operation of the display device 100 in the public mode representing a first state will now be described, and further details of the polar control retarder 300 illustrated.

[0326] FIGURE 9A is a schematic diagram illustrating in perspective side view an arrangement of polar control retarder 300 in a public mode of operation. In the present embodiment, zero volts is supplied across liquid crystal retarder 301; and TABLE 2 describes an illustrative embodiment for the arrangement of FIGURE 9A. Features of the arrangement of FIGURE 9A not discussed in further detail can be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features. TABLE 2

[0327] The switchable liquid crystal retarder 301 comprises two surface alignment layers disposed on electrodes 413, 415 and adjacent to the liquid crystal material layer 414 and on opposite sides thereof and each disposed to provide homeotropic alignment on the adjacent liquid crystal material 414. The liquid crystal material layer 414 of the switchable liquid crystal retarder 301 comprises a liquid crystal material having a negative dielectric anisotropy. The liquid crystal molecules 414 may be pre-tilted, e.g., 88 degrees from horizontal to remove degeneracy upon switching.

[0328] In the present embodiments, desirable ranges for retardations and voltages have been established through simulation of retardant stacks and experimentation with display optical stacks. Retardance ranges that provide design configurations for various optical layers will now be described.

[0329] The liquid crystal material layer 314 has a retardance for light of wavelength 550 nm in a range of 500 nm to 1,000 nm, preferably in a range of 600 nm to 900 nm, and more preferably in a range of 700 nm to 850 nm; and the retarder 330 further comprises a passive retarder with an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardance for light of wavelength 550 nm in a range of -300 nm to -900 nm, preferably in a range of -450 nm to -800 nm, and more preferably in the range of -500 nm to -725 nm.

[0330] Alternatively, the passive polar control retarder 330 may comprise an O-plate retarder with an optical axis that is oriented with a component perpendicular to the plane of the retarder and a component in the plane of the retarder. Such a retarder may provide additional compensation for residual tilts of the liquid crystal material 414.

[0331] FIGURE 9B is a schematic diagram illustrating in side view the propagation of output light from an SLM through the optical stack of FIGURE 1A in a public mode of operation; and FIGURE 9C is a schematic graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 9B. Features of the arrangements of FIGURES 9B and 9C not discussed in further detail can be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0332] Thus, when liquid crystal retarder 301 is in a first state of said two states, polar control retarder 300 does not provide overall transformation of polarization component 360, 361 to emit light passing therethrough perpendicular to the plane of switchable retarder 301 or at an acute angle to the perpendicular to the plane of switchable retarder 301. That is, polarization component 362 is substantially the same as polarization component 360 and polarization component 364 is substantially the same as polarization component 361. Thus, the angular transmission profile of FIGURE 9C is transmitting substantially uniformly across a wide polar region. Advantageously, a display can be switched to a wide field of view.

[0333] FIGURE 9D is a schematic diagram illustrating in top view the propagation of ambient lighting light through the optical stack of FIGURE 1A in a public mode of operation; and FIGURE 9E is a schematic graph illustrating the variation of reflectivity with polar direction for light rays reflected from FIGURE 9D. Features of the arrangements of FIGURES 9D and 9E not discussed in further detail may be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0334] Thus, when the liquid crystal retarder 301 is in the first state of said two states, the polar control retarder 300 does not provide overall transformation of the polarization component 372 into ambient light rays 412 passing through the additional polarizer 318 and then the polar control retarder 300, which is perpendicular to the plane of the polar control retarder 300 or at an acute angle to the perpendicular to the plane of the polar control retarder 300.

[0335] In public mode operation, input light ray 412 has polarization state 372 after transmission through additional polarizer 318. For the forward and off-axis directions, no polarization transformation occurs and therefore the reflectivity for light rays 402 from reflective polarizer 302 is low. Light ray 412 is transmitted by reflective polarizer 302 and lost in display polarizers 218, 210 or in the backlight of FIGURE 1A or in optical isolator 218, 518 in an emissive SLM 38 of FIGURE 1B.

[0336] Advantageously, in a public operating mode, high luminance and low reflectivity are provided over a wide field of view. Such a display can be conveniently viewed with high contrast by multiple observers.

[0337] The appearance of the display of FIGURE 1A in public mode for the first state will now be described.

[0338] FIGURE 10A is a schematic diagram illustrating in front perspective view the observation of output light transmitted to a display operating in public mode; FIGURE 10B is a schematic diagram illustrating in front perspective view the observation of ambient light reflected from the switchable display of FIGURE 1A in public mode; and FIGURE 10C is a schematic diagram illustrating, in front perspective, the appearance of the display of FIGURE 1A operating in public mode.

[0339] Thus, the desirable off-axis viewing position for user 49 has high display luminance and is substantially free of reflections from the reflective polarizer 302. A high image visibility value can be achieved and display information conveniently resolved by multiple users. Fresnel reflection 605 is still present as in conventional displays and is at a customary low level. A high performance public mode is provided.

[0340] Additional retarding arrangements will now be described.

[0341] FIGURE 11A is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a public mode of operation wherein the switchable retarder comprises a homogeneously aligned switchable liquid crystal layer and cross-plate A polar control retarders; FIGURE 11B is a schematic graph illustrating the variation of output luminance with polar direction for transmitted light rays in FIGURE 11A in a privacy mode of operation; FIGURE 11C is a schematic graph illustrating the variation in reflectivity with polar direction for reflected light rays in FIGURE 11A in a privacy mode of operation; FIGURE 11D is a schematic graph illustrating the variation of output luminance with polar direction for transmitted light rays in FIGURE 11A in a public mode of operation; and FIGURE 11E is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 11A in a public mode of operation comprising the embodiments illustrated in TABLE 3A. Features of the arrangements of FIGURES 11A through 11E not discussed in more detail may be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features. TABLE 3A

[0342] The switchable liquid crystal retarder 301 comprises two surface alignment layers 419a, 419b disposed adjacent to the liquid crystal material layer 421 and on opposite sides thereof and each disposed to provide homogeneous alignment in the adjacent liquid crystal material 421. The layer 314 of the liquid crystal material 421 of the switchable liquid crystal retarder 301 comprises a liquid crystal material 421 having a positive dielectric anisotropy. The liquid crystal material layer 421 has a retardance for light having a wavelength of 550 nm in a range of 500 nm to 900 nm, preferably in a range of 600 nm to 850 nm, and more preferably in a range of 700 nm to 800 nm. The retarder 330 further comprises a pair of passive retarders 330A, 330B having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the pair of passive retarders has a retarder for light of wavelength 550 nm in a range of 300 nm to 800 nm, preferably in a range of 350 nm to 650 nm and more preferably in a range of 450 nm to 550 nm.

[0343] Compared to the embodiments of TABLE 2, the passive polar control retarder 330 is provided by a pair of A plates 330A, 330B having crossed axes. In the present embodiments, “crossed” refers to an angle of substantially 90° between the optical axes of the two retarders in the plane of the retarders. To reduce the cost of the retarder materials, it is desirable to provide materials with some variation in retarder orientation due to stretching errors during film manufacture, for example. Variations in retarder orientation away from the preferred directions can reduce front luminance and increase minimum transmission. Preferably, the angle 310A is at least 35° and at most 55°, more preferably at least 40° and at most 50°, and most preferably at least 42.5° and at most 47.5°. Preferably, angle 310B is at least 125° and at most 145°, more preferably at least 130° and at most 135°, and most preferably at least 132.5° and at most 137.5°.

[0344] In comparison to the embodiments of TABLE 2, the alignment of the liquid crystal retarder is provided by a homogeneous rather than a homeotropic alignment. The homogeneous alignment advantageously provides a reduced recovery time during mechanical distortions, such as when touching the display.

[0345] Passive retarders can be provided using stretched films to advantageously achieve low cost and high uniformity. An additional field of view for liquid crystal retarders with homogeneous alignment is increased, providing resilience to the visibility of the liquid crystal material flow during applied pressure.

[0346] It may be desirable to provide the additional polarizer 318 with an electric vector transmission direction different from the electric vector transmission direction of the output polarizer 218 and the reflective polarizer 302.

[0347] FIGURE 11F is a schematic diagram illustrating in perspective side view an arrangement of retarders 300 in a privacy mode of operation comprising the passive polar control retarders of cross-plate A 330A, 330B and the homogeneously aligned switchable liquid crystal retarder 301, further comprising a passive rotation retarder 460 comprising the embodiments illustrated in TABLE 3B. Features of the arrangement of FIGURE 11F not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features. TABLE 3B

[0348] The reflective polarizer 302 and the additional polarizer 318 have electric vector transmission directions 303, 319 that are not parallel, and the display device 100 further comprises a rotator retarder 406 disposed between the reflective polarizer 302 and the additional polarizer 318, the rotator retarder 406 being arranged to rotate a polarization direction of polarized light incident thereon between the electric vector transmission direction of the display polarizer 218 and the electric vector transmission direction of the additional polarizer 318.

[0349] The output polarizer 218 and the reflective polarizer 302 may be provided with electric vector transmission directions 219, 303 that may be, for example, at an angle 317 of 45 degrees in the case of a twisted nematic LCD display. The additional polarizer 318 may be arranged to provide vertically polarized light to a user who may be wearing polarized sunglasses that normally transmit vertically polarized light.

[0350] Passive rotation retarder 460 is different from polar control retarder 330 of the present embodiments and its operation will now be described. Passive rotation retarder 460 may comprise a birefringent material 462 and be a half wave plate, with retardation at a wavelength of 550 nm of 275 nm, for example. Passive rotation retarder 460 has a fast axis orientation 464 that is tilted at an angle 466 that may be 22.5 degrees relative to the electric vector transmission direction 319 of additional polarizer 318. Passive rotation retarder 460 thus rotates the polarization of output polarizer 218 such that the polarization direction of light that is incident on polar control retarder 330B is parallel to direction 319.

[0351] In operation, passive rotation retarder 460 modifies the polarization state on the geometric axis by providing an angular rotation of the polarization component from output polarizer 218. In comparison, polar control retarders 330A, 330B together do not modify the polarization state on the geometric axis. Furthermore, passive rotation retarder 460 provides a polarization rotation that provides only a small variation of output luminance with viewing angle for off-axis directions. In comparison, polar control retarders 330A, 330B provide substantial modifications of output luminance with viewing angle.

[0352] Advantageously, a display may be provided with an output polarization direction 319 that is different from the polarization direction of the display polarizer 219, for example, to provide viewing with polarizing sunglasses.

[0353] In an alternative embodiment, the separate retarder 460 may be omitted, and the retardance of retarder 330B of FIGURE 11A increased to provide half-wave rotation. To continue the illustrative embodiment, the retardance of retarder 330B at a wavelength of 550 nm may be 275 nm greater than the retardance of retarder 330A. Advantageously, the number of layers, complexity, and cost may be reduced.

[0354] In other embodiments, passive rotation retarder 460 may be provided between display output polarizer 218 and reflective polarizer 302 such that the electric vector transmission directions 303, 319 of reflective polarizer 302 and additional polarizer 318 are parallel.

[0355] FIGURE 12A is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising a homogeneously aligned switchable liquid crystal retarder comprising liquid crystal 421 and a passive negative C plate retarder 330 driven with a second voltage V1; and FIGURE 12B is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising a homogeneously aligned switchable liquid crystal retarder and a passive negative C plate retarder driven with a second voltage V2 different from the first voltage V1. Features of the arrangements of FIGURES 12A and 12B not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0356] Compared to the arrangement of FIGURE 12A, the drive voltage V2 is increased to provide increased tilt for the molecules of the liquid crystal material 414 in the center of the liquid crystal retarder layer 314. This increased tilt changes the retardation of the switchable liquid crystal retarder 301 between privacy and public modes.

[0357] FIGURE 12C is a schematic graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 12A in a privacy mode of operation; and FIGURE 12D is a schematic graph illustrating the variation in reflectivity with polar direction for the reflected light rays in FIGURE 12A in a privacy mode of operation. FIGURE 12E is a schematic graph illustrating the variation of output luminance with polar direction for the transmitted light rays in FIGURE 12B in a public mode of operation; and FIGURE 12F is a schematic graph illustrating the variation in reflectivity with polar direction for the reflected light rays in FIGURE 12B in a public mode of operation. Illustrative embodiments of the arrangement of homogeneous alignment in combination with passive retarders are shown in Table 4A. TABLE 4A

[0358] The switchable liquid crystal retarder 301 comprises two surface alignment layers disposed adjacent to the liquid crystal material layer and on opposite sides thereof and each disposed to provide homogeneous alignment in the adjacent liquid crystal material 414. The liquid crystal material layer 414 of the switchable liquid crystal retarder 301 comprises a liquid crystal material 414 having a positive dielectric anisotropy. The liquid crystal material layer 414 has a retardance for light having a wavelength of 550 nm in a range of 500 nm to 900 nm, preferably in a range of 600 nm to 850 nm, and more preferably in a range of 700 nm to 800 nm. The retarder 330 further comprises a passive retarder with an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardance for light of wavelength 550 nm in a range of -300 nm to -700 nm, preferably in a range of -350 nm to -600 nm and more preferably from -400 nm to -500 nm.

[0359] Compared to FIGURE 11A, advantageously the thickness and complexity of the retarder 330 may be reduced.

[0360] A structure that omits the passive polar control retarder 330 will now be described.

[0361] FIGURE 13A is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising a homogeneously aligned switchable liquid crystal retarder 301 in a privacy mode of operation. The switchable liquid crystal retarder 301 comprises surface alignment layers 419a, 419b disposed adjacent to the liquid crystal material layer 421 and arranged to provide homogeneous alignment in the adjacent liquid crystal material 421. FIGURE 13B is a schematic graph illustrating the variation of output luminance with polar direction for light rays transmitted in FIGURE 13A in a privacy mode of operation; FIGURE 13C is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected in FIGURE 13A in a privacy mode of operation; FIGURE 13D is a schematic graph illustrating the variation of output luminance with polar direction for transmitted light rays in FIGURE 13A in a public mode of operation; and FIGURE 13E is a schematic graph illustrating the variation in reflectivity with polar direction for reflected light rays in FIGURE 13A in a public mode of operation.

[0362] An illustrative embodiment of the arrangement of FIGURE 13A is shown in TABLE 4B. TABLE 4B

[0363] The switchable liquid crystal retarder 301 comprises two surface alignment layers disposed adjacent to the liquid crystal material layer and on opposite sides thereof and each disposed to provide homogeneous alignment in the adjacent liquid crystal material 414. The liquid crystal material layer of the switchable liquid crystal retarder comprises a liquid crystal material having a positive dielectric anisotropy. The liquid crystal retarder 301 may have a retardance for light of wavelength 550 nm in a range of 500 nm to 1500 nm, preferably in a range of 700 nm to 1200 nm, and most preferably in a range of 800 nm to 1000 nm.

[0364] The embodiments of FIGURES 13A-13E advantageously achieve reduced cost and complexity since no passive retarder is provided. Furthermore, the public mode may be a non-driven state of the liquid crystal material of layer 314 and a relatively low voltage is used in the privacy mode. Furthermore, compared to homeotropic alignment, homogeneous alignment layers may advantageously provide reduced visibility of the flow of liquid crystal material arising from handling the display surface, e.g., when a touch panel is used.

[0365] FIGURE 13F is a schematic diagram illustrating in perspective side view a viewing angle control element comprising a reflective polarizer, a switchable liquid crystal retarder, and an additional polarizer. A low-cost, switchable aftermarket layer may be provided that provides privacy to a switchable “target” field of view profile.

[0366] Additional arrangements of switchable retarders 300 will now be described.

[0367] FIGURE 14A is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising passive cross-plate A-retarders 330A, 330B and homeotropically aligned switchable liquid crystal retarder 301. FIGURE 14B is a schematic graph illustrating the variation of output luminance with polar direction for light rays transmitted in FIGURE 14A in a privacy mode of operation; and FIGURE 14C is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected in FIGURE 14A in a privacy mode of operation. Features of the arrangements of FIGURES 14A through 14C not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0368] FIGURE 14D is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a public mode of operation comprising passive cross-plate A-retarders and a homeotropically aligned switchable liquid crystal retarder. FIGURE 14E is a schematic graph illustrating the variation of output luminance with polar direction for light rays transmitted in FIGURE 14D in a public mode of operation; and FIGURE 14F is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected in FIGURE 14D in a public mode of operation. Features of the arrangements of FIGURES 14D through 14F not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0369] Thus, the passive polar control retarder 330 comprises a pair of retarders 330A, 330B having optical axes in the plane of the retarders that are crossed. The pair of retarders 330A, 330B have optical axes that extend +/- 45° relative to the electric vector transmission direction of the output polarizer. The pair of retarders 330A, 330B each comprise a single plate A. An illustrative embodiment is described in Table 5. TABLE 5

[0370] The switchable liquid crystal retarder 301 comprises two surface alignment layers disposed on electrodes 413, 415 and adjacent to the liquid crystal material layer 414 and on opposite sides thereof and each disposed to provide homeotropic alignment on the adjacent liquid crystal material 414. The liquid crystal material layer 414 of the switchable liquid crystal retarder 301 comprises a liquid crystal material having a negative dielectric anisotropy. The liquid crystal material layer 314 has a retardance for light of wavelength 550 nm in a range of 500 nm to 1,000 nm, preferably in a range of 600 nm to 900 nm, and most preferably in a range of 700 nm to 850 nm. The retarder 301 further comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the pair of passive retarders has a retardance for light of wavelength 550 nm in a range of 300 nm to 800 nm, preferably in the range of 500 nm to 700 nm and more preferably in the range of 550 nm to 675 nm.

[0371] Advantageously, high reflectivity can be provided over a wide field of view in privacy mode. A-plates can be manufactured more conveniently at a lower cost than for C-plate retardants.

[0372] Hybrid aligned liquid crystal retarders 301 will now be described.

[0373] FIGURE 15A is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising a homogeneously and homeotropically aligned switchable liquid crystal retarder 301 comprising liquid crystal material 423 and a passive negative C plate retarder 330. FIGURE 15B is a schematic graph illustrating the variation of output luminance with polar direction for light rays transmitted in FIGURE 15A in a privacy mode of operation; and FIGURE 15C is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected in FIGURE 15A in a privacy mode of operation. FIGURE 15D is a schematic graph illustrating the variation of output luminance with polar direction for light rays transmitted in FIGURE 15A in a public mode of operation; and FIGURE 15E is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 15A in a public mode of operation. Features of the arrangements of FIGURES 15A through 15E not discussed in more detail may be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0374] One embodiment of the hybrid alignment arrangement comprising homeotropic and homogeneous alignment layers in combination with a passive retarder is illustrated in TABLE 6. TABLE 6

[0375] The switchable liquid crystal retarder 301 comprises two surface alignment layers 419a, 419b disposed adjacent to layer 314 of liquid crystal material 414 and on opposite sides thereof, wherein one of the surface alignment layers 419a is disposed to provide homeotropic alignment in the adjacent liquid crystal material 414 and the other of the surface alignment layers 419b is disposed to provide homogeneous alignment in the adjacent liquid crystal material 414.

[0376] Compared to embodiments with two homeotropic alignment layers or two homogeneous alignment layers, the design of passive polar control retarder 330 may be different if placed on the side of homeotropic alignment layer 419a or placed on the side of homogeneous alignment layer 419b.

[0377] When the surface alignment layer 419b arranged to provide homogeneous alignment is between the layer 314 of the liquid crystal material 414 and the polar control retarder 330, the liquid crystal retarder 301 has a retardance for light of a wavelength of 550 nm in a range of 700 nm to 2000 nm, preferably in the range of 1000 nm to 1500 nm and most preferably in the range of 1200 nm to 1500 nm. The polar control retarder 300 may further comprise a passive polar control retarder 330 having its optical axis perpendicular to the plane of the retarder, wherein the passive polar control retarder 330 has a retardance for light of a wavelength of 550 nm in a range of -400 nm to -1,800 nm, preferably in a range of -700 nm to -1,500 nm, and most preferably in the range of -900 nm to -1,300 nm.

[0378] Plate C of FIGURE 15A may be replaced by crossed plates A. When the polar control retarder 300 further comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, each retarder of the retarder pair having a retardance for light of wavelength 550 nm in a range of 400 nm to 1800 nm, preferably in a range of 700 nm to 1500 nm and more preferably in the range of 900 nm to 1300 nm.

[0379] When the surface alignment layer 419a arranged to provide homeotropic alignment is between the layer 314 of the liquid crystal material 414 and the polar control retarder 330, the liquid crystal retarder 301 has a retardance for light of a wavelength of 550 nm in a range of 500 nm to 1800 nm, preferably in the range of 700 nm to 1500 nm, and most preferably in the range of 900 nm to 1350 nm. The polar control retarder 300 may further comprise a passive polar control retarder 330 having its optical axis perpendicular to the plane of the retarder 330, wherein the passive polar control retarder 330 has a retardation for light of a wavelength of 550 nm in a range of -300 nm to -1,600 nm, preferably in a range of -500 nm to -1,300 nm, and more preferably in the range of -700 nm to -1,150 nm; or the retarder 330 may further comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each retarder of the pair of retarders has a retardance for light of wavelength 550 nm in a range of 400 nm to 1600 nm, preferably in the range of 600 nm to 1400 nm and more preferably in the range of 800 nm to 1300 nm.

[0380] Advantageously, the hybrid alignment of FIGURE 15A achieves a greater polar angular range over which the reflectivity of the reflective polarizer 302 is increased.

[0381] Additional display structures comprising multiple optical stacks will now be described to achieve field of view control of a privacy or low stray light display apparatus.

[0382] FIGURE 16 is a schematic diagram illustrating in perspective side view a switchable privacy visor 100 for use in ambient lighting comprising a non-collimating backlight 20, an additional passive polar control retarder 300B disposed between a reflective recirculating polarizer 318B and the transmissive SLM 48, a reflective polarizer 302, polar control retarder 300A, and additional polarizer 318A. Thus, compared to the visor of FIGURE 1A, FIGURE 16 further comprises an additional passive polar control retarder 300B disposed between the input polarizer 210 of the transmissive SLM 48 and the other additional polarizer 318B. A further additional polarizer 318B is provided by reflective polarizer 318B arranged to recirculate light in the backlight 20 and advantageously increase efficiency in a manner similar to reflective polarizer 208 of FIGURE 1A.

[0383] Advantageously, the field of view of the display is modified by the further additional polarizer 318B to reduce off-axis luminance of the SLM 48. Stray light is reduced and the level of visual security against an eavesdropper is increased. The further polarizer 318B may be a reflective polarizer. This is different from the reflective polarizer 302. The further reflective polarizer 318B provides light recirculation in the backlight 20 and does not increase forward reflection in privacy mode. Advantageously, efficiency is increased.

[0384] FIGURE 17A is a schematic diagram illustrating in side view a switchable privacy visor for use in ambient lighting comprising an emissive SLM 48, a passive control retarder 300B, an additional polarizer 318B, a reflective polarizer 302, multiple retarders 300, and an additional polarizer 318A. An additional polar control retarder 300B is disposed between the output polarizer 218 and the reflective polarizer 302. An additional polarizer 318A is disposed between the additional polar control retarder 300B and the reflective polarizer 302.

[0385] FIGURE 17B is a schematic diagram illustrating in side perspective view a 260° viewing angle control element for an emissive display.

[0386] In operation, the light from the display output polarizer 218 has a modification of the field of view of the passive polar control retarder 300B and the additional polarizer 318B. Advantageously, the field of view of the emissive display is reduced. The reflective polarizer 302, the multiple polar control retarders 300A, and an additional polarizer 318A provide switching between a public mode determined by the SLM 48, the retarder 300B, and the other additional polarizer 318B and a privacy mode with high off-axis reflectivity and on-axis luminance reduction compared to that achieved by the display 100 of FIGURE 1B.

[0387] Compared to the display of FIGURE 1B, FIGURE 17A further comprises an additional polar control retarder 300B and an additional polarizer 318B, wherein the additional polar control retarder 300B is disposed between the aforementioned additional polarizer and the other additional polarizer 318.

[0388] It would be desirable to provide a public mode with high image visibility for off-axis viewing and a privacy mode with a high level of visual security. Embodiments of switchable privacy displays comprising multiple other retarders and other additional polarizers will now be described.

[0389] FIGURE 18A is a schematic diagram illustrating in side view a switchable privacy visor 100 for use in ambient lighting 604 comprising a wide-angle backlight 20, wherein a first polar control retarder 300A is disposed between the backlight 20 and the SLM 48 and another polar control retarder 300B is disposed to receive light from the SLM 48. Features of the arrangements of FIGURES 16-18B not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0390] FIGURE 18A has a structure similar to FIGURE 1A with view angle control element 260A provided to receive light from output polarizer 218 of the SLM.

[0391] By way of comparison, the backlight 20 may be provided by a wide-angle backlight 20, as described elsewhere, rather than a directional backlight. The SLM 48 is a transmissive SLM arranged to receive the output light 400 from the backlight 20, and the SLM 48 further comprises an input polarizer 210 disposed on the input side of the SLM 48, the input polarizer 210 being a linear polarizer. A further polarizer 318B is disposed on the input side of the input polarizer 210, the further polarizer 318B being a linear polarizer. At least one further polar control retarder 300B is disposed between the further polarizer 318B and the input polarizer 210.

[0392] The at least one first-mentioned polar control retarder 300A comprises a first switchable liquid crystal retarder 301A comprising a first layer 314A of liquid crystal material and the at least one other polar control retarder 300B comprises a second switchable liquid crystal retarder 301B comprising a second layer 314B of liquid crystal material.

[0393] Polar control retarder 300A comprises passive polar control retarder 330A and switchable liquid crystal retarder 301A. Additional polar control retarder 300B comprises passive polar control retarder 330B and switchable liquid crystal retarder 301B. Polar control retarder 300B provides a modification of the output transmission polar luminance profile and polar control retarder 300A provides a modification of the output transmission polar luminance and reflectivity profiles, as described elsewhere herein.

[0394] In comparison to FIGURE 16 , increased off-axis luminance is achieved in public mode since the backlight 20 has higher luminance for off-axis polar locations, so that image visibility is increased for off-axis users by controlling both liquid crystal layers 314A, 314B. In privacy mode, the level of visual security is increased for off-axis onlookers due to the fact that off-axis luminance is reduced by two multiplicative luminance control polar control retarders 300A, 300B and respective additional polarizers 318A, 318B. Additional high reflectivity is provided for off-axis users.

[0395] Advantageously, the reflective recirculation polarizer operating as described with reference to FIGURE 1A (which is different in function from the reflective polarizer 302) may provide the other additional polarizer 318B to achieve even higher efficiency and reduced field of view for privacy operation.

[0396] The arrangement of FIGURE 18A has a single viewing angle control element 260A on the front surface of the SLM 48. Advantageously, the front of the display thickness can be reduced. Additional diffusers can be arranged on the front surface of the polarizer 318 or between the viewing angle control element 260A and the output polarizer 218. Advantageously, the visibility of reflections from the front surface can be reduced. Furthermore, the viewing angle control element 260B can be conveniently provided between the SLM 48 and the backlight 20. The cost and complexity of the assembly can be reduced. The number of surfaces between the pixel layer 214 and the display user 26 can be advantageously reduced, achieving greater image contrast.

[0397] An arrangement similar to FIGURE 18A, wherein passive retarders 330A, 330B comprise a pair of multiple passive retarders, will now be described.

[0398] FIGURE 18B is a schematic diagram illustrating in front view the alignment of optical layers of an optical stack comprising polar control retarder 300A disposed between a reflective polarizer 302 and an additional polarizer 318A and another polar control retarder 300B disposed between input polarizer 210 and another additional polarizer 318B of a transmissive SLM 48, wherein polar control retarder 300A and another polar control retarder 300B comprise crossed plates A. An illustrative embodiment is provided in TABLE 7 and TABLE 8A.

[0399] TABLE 7 TABLE 8A

[0400] Compared to the embodiment of FIGURE 11A, the embodiment of FIGURES 18A-18F comprises a transmissive SLM 48 having high luminance in the wide field of view and a wide-angle backlight 20 or an emissive SLM 48.

[0401] Further embodiments include polar control retarder 300A, additional polarizer 318A, another polar control retarder 300B, and another additional polarizer 318B. The transmission profiles of such arrangements are multiplicative. Thus, very low luminance can be achieved at design polar angles, such as at a +/- 45 degree lateral angle and 0 degree elevation. However, high luminance of the backlight or emissive SLM at angles higher than the design polar angle provides increased light levels and reduced reflectivity. The level of visual safety can be reduced for high angle onlookers. The at least one other polar control retarder 300B comprises at least one other passive retarder, in the embodiment of FIGURE 18B two crossed passive polar control retarders 330BA, 330BB are provided.

[0402] It may be desirable to provide designs tuned to minima that are at lateral angles greater than 45 degrees, e.g., between 50 degrees and 65 degrees. In arrangements with another polar control retarder 300B, layers 314A, 314B of liquid crystal material 414 of switchable liquid crystal retarders 301A, 301B may each have a retardance for light of a wavelength of 550 nm in a range of 450 nm to 850 nm, preferably in a range of 500 nm to 750 nm, and most preferably in a range of 550 nm to 650 nm.

[0403] The first-mentioned multiple retarders and the multiple other retarders may each comprise a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the first-mentioned pair of passive retarders 330A, 330B has a retardance for light of wavelength 550 nm in a range of 300 nm to 800 nm, preferably in a range of 350 nm to 650 nm, and more preferably in a range of 400 nm to 550 nm.

[0404] Advantageously, the luminance and reflectivity at high angles can be reduced and the level of visual safety can be increased for onlookers at a high viewing angle. Reducing color asymmetry in the switchable privacy display will now be discussed.

[0405] FIGURE 18C is a schematic graph illustrating the logarithmic output luminance variation with polar direction for light rays transmitted from multiple retarders comprising crossed passive A plates and a homogeneously aligned switchable liquid crystal retarder to one of polar control retarders 300B comprising crossed A plate retarders 330AA, 330AB and liquid crystal layer 314A of TABLE 8A; and FIGURE 18D is a schematic graph illustrating in a lateral direction the logarithmic output luminance variation 470A with lateral viewing angle for light rays transmitted from multiple retarders comprising crossed passive A plates and a homogeneously aligned switchable liquid crystal retarder to one of polar control retarders 300B comprising retarders 330AA, 330AB, 314A of TABLE 8B.

[0406] FIGURES 18C and FIGURE 18D illustrate that there is some luminance asymmetry that is provided by the sequence of crossed A plates 330AA, 330AB. Since luminance profiles are wavelength dependent, in operation this asymmetry can provide a noticeable color shift that has a different appearance on either side of the display, as illustrated in angled regions 472L, 472R. In the arrangement of FIGURE 11A, this color shift is typically not very visible due to the low luminance of the collimated backlight 20. However, as the luminance of the backlight 20 increases at high angles, or for emissive SLMs, then the asymmetry is more clearly visible. It would be desirable to provide an asymmetric color appearance.

[0407] Turning to FIGURE 18B, the first-mentioned polar control retarder 300A comprises a pair of passive retarders 330AA, 330AB having optical axes 331AA, 331AB in the plane of the retarders 330AA, 330AB that are crossed, wherein the first of the pair of passive retarders 330AA has an optical axis 331AA that extends 45° to an electric vector transmission direction 219 of the output polarizer 218, and the second of the pair of passive retarders 331AB has an optical axis 331AB that extends 135° to the electric vector transmission direction 219 of the output polarizer 218.

[0408] The at least one additional polar control retarder 300B comprises an additional pair of passive retarders 330BA, 330BB having optical axes 331BA, 331BB in the plane of the retarders 330BA, 330BB that are crossed, wherein the first of the additional pair of passive retarders 330BA has an optical axis 331BA that extends 135° relative to an electric vector transmission direction 219 of the output polarizer 218, and the second of the additional pair of passive retarders 330BB has an optical axis 331BB that extends 45° relative to an electric vector transmission direction 219 of the output polarizer 218. The second retarder 330AB, 330BB of each pair of passive retarders is arranged to receive light from the first retarder 330AA, 330BA of the respective passive polar control retarder pair 330A, 330B. Thus, the passive retarder 330 AA of the first pair and the passive retarder 330BB of the other pair that are closest to each other have respective optical axes 331AA and 331AB extending in the same direction.

[0409] For the present disclosure, the direction of rotation of the optical axes of the passive retarder may be clockwise or counterclockwise, such that any of the optical axes within each pair of passive retarders extends 45° and 135°, respectively. In the illustrative example, the direction of rotation is clockwise.

[0410] Returning to FIGURE 18D, the luminance profile of the crossed A plates 330BA 330BB and the liquid crystal retarder 314B is illustrated by profile 470B. In combination, profiles 470A, 470B are multiplicative. The arrangement of the retarders of FIGURE 18B thus achieves an average of the two luminance profiles and further achieves color symmetry. Advantageous angular uniformity is improved.

[0411] Optionally, in the example of FIGURES 18A and 18B, reflective polarizer 318B may be omitted. In this case, reflective polarizer 318B may optionally be replaced with a dichroic absorbing polarizer (not shown).

[0412] Another arrangement of the polar control retarder 300A and the other polar control retarder 300B will now be given.

[0413] FIGURE 18E is a schematic diagram illustrating in side view a switchable privacy visor for use in ambient lighting comprising an emissive SLM 48, a first polar control retarder 300A, a first additional polarizer 318A, a reflective polarizer 302, a second polar control retarder 300B, and a second additional polarizer 318B; and FIGURE 18F is a schematic diagram illustrating in front view the alignment of optical layers of an optical stack comprising polar control retarders 300A disposed between an additional light absorbing polarizer 318A and another additional polarizer 318B that is a reflective polarizer 302 and other polar control retarders 300B disposed between output polarizer 218 and another additional polarizer 318B, 302, wherein polar control retarders 300A and multiple other retarders 300B comprise crossed A plates 330AA, 330AB, 330BA, and 330BB.

[0414] An illustrative embodiment is provided in TABLE 8B. TABLE 8B

[0415] Compared to the arrangement of FIGURE 18A, reduced luminance for off-axis viewing locations may be advantageously provided since the dispersion of the SLM 48 does not modify the field of view luminance profile from the viewing angle control element 260B. Furthermore, a single optical component stack may be provided for convenient aftermarket or factory fitment.

[0416] The embodiment of FIGURES 18E and 18F further illustrates that reflective polarizer 302 may further provide additional polarizer 318B of multiple other retarders 300B. Advantageously, cost and thickness are reduced and efficiency is increased.

[0417] Embodiments of luminance control displays with symmetrical color and luminance output will now be described.

[0418] FIGURE 18G is a schematic diagram illustrating in front view the alignment of optical layers of an optical stack comprising polar control retarders 300A disposed between an additional light absorption polarizer 318A and an additional polarizer 318B and further additional polar control retarders 300B disposed between output polarizer 218 and further additional polarizer 318B, wherein polar control retarders 300A and multiple further retarders 300B each comprise cross-plate A retarders 330AA, 330AB, 330BA, and 330BB.

[0419] A display device thus comprises: an SLM 48; a display polarizer disposed on at least one side of the SLM, the display polarizer being a linear polarizer; a first additional polarizer 318A disposed on the same side of the SLM 48 as one of the at least one display polarizer, the first additional polarizer 318A being a linear polarizer; and first polar control retarders 300A disposed between the first additional polarizer 318A and the one of the at least one display polarizer; a further additional polarizer 318B disposed on the same side of the SLM as said one of the at least one display polarizer, outside the first additional polarizer 318A, the other additional polarizer 318B being a linear polarizer; and additional polar control retarders 300B disposed between the first additional polarizer 318A and the other additional polarizer 318B, wherein the first polar control retarders comprise a pair of passive retarders 330AA, 330AB having optical axes 331AA, 331AB in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, with respect to an electric vector transmission direction of the output polarizer 218, the other polar control retarders comprise a further pair of passive retarders 330BA, 330BB having optical axes 331BA, 331BB in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, with respect to the electric vector transmission direction of the output polarizer 218, and the optical axes 331BB, 331AA of the first one of the pair of passive polar control retarders and of the one of the other pair of closest passive polar control retarders extend in the same direction.

[0420] The first polar control retarders 300A and the further polar control retarders 300B further comprise a switchable liquid crystal retarder 301A, 301B comprising a layer 314A, 314B of liquid crystal material 414A, 414B, wherein the first polar control retarders 300A and the further polar control retarders 300B are each arranged, in a switchable state of the switchable liquid crystal retarder 301A, 301B, simultaneously to introduce no net relative phase shift to orthogonal polarization components of light passed through said one of the at least one display polarizers along an axis along a line perpendicular to the plane of the polar control retarders and to introduce a net relative phase shift to orthogonal polarization components of light passed through said one of the at least one display polarizers along an axis inclined to the perpendicular line of the polar control retarders. plans of polar control retarders.

[0421] The example of FIGURE 18G is the same as that of FIGURES 18E and 18F, except that reflective polarizer 302 is replaced by additional polarizer 318B. Advantageously, a luminance control display with symmetrical color and luminance output in the lateral direction can be achieved in the same manner as illustrated by FIGURES 18C and 18D. Furthermore, the reflectivity of reflective polarizer 302 is eliminated for environments where high off-axis reflectivity is undesirable.

[0422] FIGURE 18H is a schematic diagram illustrating in front view the alignment of optical layers of an optical stack for a transmissive SLM 48 comprising multiple other retarders 300B disposed between an additional light absorbing polarizer 318B and an additional polarizer 318A and multiple retarders 300A disposed between input polarizer 210 and additional polarizer 318A, wherein multiple retarders 300A and multiple other retarders 300B comprise crossed plates A.

[0423] The example of FIGURE 18H is the same as that of FIGURE 18G, except that the optical stack is disposed on the input side of an SLM and between the backlight 20 and the SLM 48. Advantageously, the thickness of the front of the display is reduced and greater diffusion can be provided on the front surface without blurring the pixels. Further image contrast can be increased.

[0424] FIGURE 18I is a schematic diagram illustrating in front view the alignment of optical layers of an optical stack for a transmissive SLM 48 comprising multiple other retarders 300B disposed between an additional polarizer 318B and input polarizer 210; and multiple retarders 300A disposed between output polarizer 218 and an additional polarizer 318A, wherein multiple retarders 300A, 300B, and multiple other retarders comprise crossed A plates 330AA, 330AB, 330BA, 330BB.

[0425] A display device comprises: a backlight 20 arranged to emit light, a transmissive SLM 48 arranged to receive light output from the backlight 20; an input polarizer 210 arranged on the input side of the SLM 48 and an output polarizer 218 arranged on the output side of the SLM 48, the input polarizer 210 and the output polarizer 218 being linear polarizers; a first additional polarizer 318A arranged on the output side of the output polarizer 218, the first additional polarizer 318A being a linear polarizer; and first polar control retarders 300A arranged between the first additional polarizer 318A and the output polarizer 218; a further additional polarizer 318B arranged between the backlight 20 and the input polarizer 210, the further additional polarizer 318B being a linear polarizer; and other polar control retarders 300B disposed between the input polarizer 210 and the other additional polarizer 318B; wherein the first polar control retarders 300A comprises a pair of passive retarders 330AA, 330AB having optical axes 331AA, 331AB in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, with respect to an electric vector transmission direction of the output polarizer 218, the other polar control retarders 300B comprises an additional pair of passive retarders 330BA, 330BB having optical axes 331BA, 331BB in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, with respect to an electric vector transmission direction of the output polarizer 218, and the optical axes 331BB, 331AA of the one of the first pair of passive polar control retarders and of the one of the other pair of polar control retarders passives closest to each other extend in the same direction.

[0426] The example of FIGURE 18I is the same as that of FIGURE 18H, except that the optical stack is disposed on either side of an SLM 48 and between the backlight 20 and the SLM 48. Advantageously, the stray light from the SLM does not provide stray light to the onlooker, and a higher level of visual safety can be achieved.

[0427] FIGURE 18J is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising a negative C-plate passive polar control retarder 330A and a homogeneously aligned switchable liquid crystal retarder 301A disposed between output polarizer 218 and reflective polarizer 302 and a negative C-plate passive polar control retarder 330B and a homogeneously aligned switchable liquid crystal retarder 301B disposed between absorption polarizer 318 and reflective polarizer 302 in a privacy mode of operation. Thus, the display device may further comprise a retardance control layer 300A disposed between the output polarizer 218 and the reflective polarizer 302. The retardance control layer 300A may comprise another switchable liquid crystal retardant 301A disposed between the output polarizer 218 and the reflective polarizer 302.

[0428] The first-mentioned polar control retarder 300B comprises a first switchable liquid crystal retarder 301B comprising a first layer of liquid crystal material 414B, and the other polar control retarder 300A comprises a second switchable liquid crystal retarder 301A comprising a second layer of liquid crystal material 414A. The other switchable liquid crystal retarder 301A comprises a surface alignment layer 307A disposed adjacent to the liquid crystal material 414A having a pre-tilt with a pre-tilt direction with an in-plane component of the liquid crystal material layer that is aligned parallel or antiparallel or orthogonal to the reflective polarizer.

[0429] The pre-tilt directions 307A, 331A of the alignment layers of the other switchable liquid crystal retarder 301A may have a component in the plane of the liquid crystal layer 314A that is aligned parallel or antiparallel or orthogonal to the pre-tilt directions of the alignment layers 307B, 331B of the first switchable liquid crystal retarder 301B. In a public mode of operation, the two switchable liquid crystal layers 301B, 301A are actuated to provide a wide viewing angle. In a privacy mode of operation, the switchable liquid crystal retarders 301A, 301B may cooperate to advantageously achieve greater luminance reduction and thereby improve privacy on a single geometric axis.

[0430] The first and second liquid crystal retarders 301A, 301B may have different retardances. The retardance provided by the first liquid crystal retarder 301B and the other liquid crystal layer 314A may be different. The control system 352 may be arranged to control the application of a common voltage across the first and second switchable liquid crystal retarders 301A, 301B. The liquid crystal material 414B of the first liquid crystal retarder 301B may be different from the liquid crystal material 414A of the second liquid crystal layer 301A. The chromatic variation of the polar luminance profiles illustrated elsewhere herein may be reduced, so that off-axis color appearance is advantageously improved.

[0431] Alternatively, the switchable liquid crystal retarders 301A, 301B may have orthogonal alignments such that reduced luminance is achieved in both the horizontal and vertical directions to advantageously achieve landscape and portrait privacy operation.

[0432] The retardance control layer 300A may comprise a passive polar control retarder 330A disposed between the output polarizer 218 and the reflective polarizer 302. More generally, the switchable liquid crystal retarder 301A may be omitted and a fixed luminance reduction may be provided by the passive retarders 330A. For example, luminance reduction in the viewing quadrants may be provided only through layer 330A. Advantageously, the polar region for luminance reduction may be achieved.

[0433] FIGURE 18J further illustrates that reflective polarizer 302 may provide another additional polarizer 318B and that dichroic polarizer 318B of FIGURE 18F, for example, may be omitted. Advantageously, increased efficiency and reduced thickness may be achieved.

[0434] FIGURE 18K is a schematic diagram illustrating in perspective side view a viewing angle control element 260 comprising a first polar control retarder 300A, a first additional polarizer 318A, a reflective polarizer 302, a second polar control retarder 300B, and a second additional polarizer 318B. Advantageously, an after-market privacy control element and/or stray light control element may be provided that does not require matching to the pixel resolution of the panel to avoid Moiré artifacts. The viewing angle control optical element 260 may further be provided for factory fit to the SLM 48. Features of the arrangements of FIGURES 18E-18H not discussed in further detail may be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0435] It may be desirable to provide entertainment and night modes of operation in a motor vehicle.

[0436] FIGURE 19A is a schematic diagram illustrating in top view a motor vehicle having a switchable directional display, as illustrated in FIGURES 19A and B, disposed within vehicle cabin 602 for daytime and/or shared modes of operation; and FIGURE 19B is a schematic diagram illustrating in side view a motor vehicle having a switchable directional display disposed within vehicle cabin 602 for daytime and/or shared modes of operation. The light cone 630, 632 has a wide angular field of view and therefore the display is advantageously visible to multiple occupants with low reflectivity.

[0437] FIGURE 19C is a schematic diagram illustrating in top view a motor vehicle having a switchable directional display, as illustrated in FIGURES 19A and 19B, disposed within vehicle cabin 602 for nighttime and/or entertainment modes of operation; FIGURE 19D is a schematic diagram illustrating in side view a motor vehicle having a switchable directional display disposed within vehicle cabin 602 for nighttime and/or entertainment modes of operation. The light cone 634, 636 has a narrow angular field of view and therefore the display is advantageously visible to only a single occupant. Off-axis occupants see increased reflections in the display, reducing visibility. Stray light advantageously for nighttime operation is reduced, increasing driver safety. Additionally, reflections from the windshield display 601 are reduced, minimizing distraction to the driver 604. Features of the arrangements of FIGURES 19A through 19D not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0438] Displays 100 comprising polar control retarders 300 which are passive retarders 272 and comprising reflective polarizer 302 and additional polarizer 318 will now be described in more detail.

[0439] FIGURE 20A is a schematic diagram illustrating in side view a privacy visor 100 for use in ambient lighting 604 comprising a backlight 20, a transmissive SLM 48, a reflective polarizer 302, passive polar control retarders 300 comprising passive retarders 272A, 272B, 272C, and 272C; and additional polarizer 318; and FIGURE 20B is a schematic diagram illustrating in perspective side view a viewing angle control element comprising a reflective polarizer 302, passive polar control retarders 300, and an additional polarizer 318.

[0440] The operation of such a display is described below with reference to FIGURES 22A-22B. Advantageously, a low-cost privacy or other type of diffuse light display may be provided. In addition, the complexity and thickness of the display are reduced compared to switchable displays 100.

[0441] FIGURE 20C is a schematic diagram illustrating in perspective side view a viewing angle control element 260 comprising passive polar control retarders 300A comprising passive retarders 272AA, 272AB, 272AC, 272AD disposed between an additional polarizer 318A and a reflective polarizer 302; and another additional polarizer 318B and other passive polar control retarders 300B comprising passive retarders 272BA, 272BB, 272BC, 272BD disposed on the input side of the reflective polarizer 302. The additional polarizer and in comparison to FIGURE 20B, the off-axis luminance advantageously can be further reduced while the front luminance can be substantially maintained when connected to the output of an SLM.

[0442] FIGURE 20D is a schematic diagram illustrating in side perspective view a privacy visor for use in ambient lighting. In comparison to FIGURE 20A, another additional polarizer 318B which is a reflective polarizer and other polar control retarders 300B comprising retarders 272BA, 272BB are arranged at the input of the SLM. The other additional polarizer 318B and 300B achieve greater luminance reduction for wide angle backlights 20. The level of visual safety can advantageously be increased for wide angle backlights. In comparison to the switchable arrangements described elsewhere, the thickness and cost are reduced. Features of the arrangements of FIGURES 20A through 20D not discussed in more detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0443] The embodiments of FIGURES 20A-20D illustrate the passive polar control retarder stack 300 comprising four passive retarders, as will be illustrated in FIGURES 22A and 22B below. However, other types of passive retarder stacks will also be described below and may be incorporated. Various combinations of polar control retarders 300 comprising passive retarders 272 disposed between a reflective polarizer 302 and an additional polarizer 318 will now be described.

[0444] FIGURE 21A is a schematic diagram illustrating in perspective side view an optical stack of a passive retarder comprising a negative C plate and arranged to provide field of view modification of a display device; and FIGURE 21B is a schematic graph illustrating the variation of output transmission with polar direction for light rays transmitted in the passive retarder of FIGURE 21A.

[0445] FIGURE 21C is a schematic diagram illustrating in perspective side view an optical stack of a passive retarder comprising a negative plate O inclined in a plane orthogonal to the electric vector transmission direction of the display polarizer and a negative plate C and arranged to provide field of view modification of a display device; and FIGURE 21D is a schematic graph illustrating the variation of output transmission with polar direction for light rays transmitted in the passive retarder of FIGURE 21C comprising the structure illustrated in TABLE 9A. TABLE 9A

[0446] Passive polar control retarder 300B thus comprises a passive retarder 272A that is a negative O-plate having an optical axis with a component in the plane of passive retarder 272A and a component perpendicular to the plane of passive retarder 272A. Furthermore, the in-plane component of the passive retarder extends 90° to an electrical vector transmission direction that is parallel to electrical vector transmission 219 of display polarizer 218. Passive retarder 272B comprises a passive retarder having an optical axis perpendicular to the plane of the passive retarder.

[0447] Advantageously, luminance may be reduced for lateral viewing directions. A mobile display may be comfortably rotated about a horizontal axis while still achieving privacy for onlookers off the axis in the lateral direction.

[0448] FIGURE 21E is a schematic diagram illustrating in perspective side view an optical stack of a passive retarder comprising crossed A plates and a positive O plate; and FIGURE 21F is a schematic graph illustrating the variation of output transmission with polar direction for light rays transmitted in the passive retarder of FIGURE 21E comprising the structure illustrated in TABLE 9B. TABLE 9B

[0449] Passive polar control retarder 300B thus comprises passive retarders 272A, 272B that are crossed A plates and retarder 272C that has an optical axis with a component in the plane of passive retarder 272C and a component perpendicular to the plane of passive retarder 272C. The in-plane component of the passive retarder extends 90° to an electrical vector transmission direction that is parallel to electrical vector transmission 219 of display polarizer 218. Advantageously, luminance may be reduced for lateral viewing directions. A movable display may be comfortably rotated about a horizontal axis while achieving privacy from onlookers off the axis in the lateral direction.

[0450] It may be desirable to provide luminance reduction in both the lateral and elevation directions.

[0451] FIGURE 22A is a schematic diagram illustrating in perspective side view an optical stack of passive retarders 272A-272D comprising two pairs of crossed plates A; and FIGURE 22B is a schematic graph illustrating the variation of output transmission with polar direction for light rays transmitted in the passive retarder of FIGURE 22A comprising the structure illustrated in TABLE 10. Features of the arrangements of FIGURES 22A and 22B not discussed in further detail may be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features. TABLE 10

[0452] The retarder thus comprises a pair of passive retarders 272A, 272D having optical axes in the plane of the retarders that are crossed. Each pair of retarders comprises a plurality of plates A with their respective optical axes aligned at different angles to each other. The pair of passive retarders 272B, 272C have optical axes that extend at 90° and 0°, respectively, to an electrical vector transmission direction that is parallel to the electrical vector transmission 211 of the display polarizer 210.

[0453] The pair of passive retarders 272A, 272D have optical axes that extend 45° and 135°, respectively, relative to an electrical vector transmission direction 211 that is parallel to the electrical vector transmission of the display polarizer 218, respectively.

[0454] The display further comprises an additional pair of passive retarders 272B, 272C disposed between the first pair of passive retarders 272A, 272D and having optical axes in the plane of the retarders that are crossed. The additional pair of passive retarders 272B, 272C have optical axes that extend 0° and 90°, respectively, relative to an electric vector transmission direction 211, 317 that is parallel to the electric vector transmission of the display polarizer 210, 316.

[0455] The retardance of each plate A to light of wavelength 550 nm may be in the range of 600 nm to 850 nm, preferably in the range of 650 nm to 730 nm, and most preferably in the range of 670 nm to 710 nm. The color shift of absorbed light from a central location to an off-axis location may be advantageously reduced.

[0456] In other illustrative embodiments, preferably angle 273A is at least 40° and at most 50°, more preferably at least 42.5° and at most 47.5°, and most preferably at least 44° and at most 46°. Preferably, angle 273D is at least 130° and at most 140°, more preferably at least 132.5° and at most 137.5°, and most preferably at least 134° and at most 136°.

[0457] In other illustrative embodiments, the inner retarder pair 272B, 272C may have looser tolerances than the outer retarder pair 272A, 272D. Preferably, angle 273B is at least -10° and at most 10°, preferably at least -5° and at most 5°, and more preferably at least -2° and at most 2°. Preferably, angle 273C is at least 80° and at most 100°, more preferably at least 85° and at most 95°, and most preferably at least 88° and at most 92°.

[0458] The present embodiment provides a transmission profile that has some rotational symmetry. Advantageously, a privacy display may be provided with reduced image visibility from a wide field of view to lateral or elevated viewing positions of an onlooker. Furthermore, such an arrangement may be used to achieve enhanced privacy operation for landscape and portrait operation of a mobile display. Such an arrangement may be provided in a vehicle to reduce stray light to off-axis passengers and also to reduce light falling on the windshield and other glass surfaces in the vehicle.

[0459] FIGURES 23A and 23B are schematic diagrams illustrating in side views part of a display comprising a switchable compensated retarder and optical bonding layers 380. Features of the arrangements of FIGURES 23A and 23B not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features. Optical bonding layers 380 can be provided to laminate films and substrates, achieving higher efficiency and reduced luminance at high viewing angles in privacy mode. Additionally, an air gap 384 can be provided between the SLM 48 and the polar control retarder 300. To reduce wetting of the two surfaces in the air gap 384, an anti-wetting surface 382 can be provided to at least one of the polar control retarder 300 or SLM 48.

[0460] Retarder 330 may be provided between switchable liquid crystal layer 314 and SLM 48, as illustrated in FIGURE 23B, or may be provided between additional polarizer 318 and switchable liquid crystal layer 314, as illustrated in FIGURE 23A. Substantially the same optical performance is provided in both systems, except in hybrid alignment as described elsewhere herein. It would be desirable to provide reduced thickness and reduced total number of optical components.

[0461] FIGURE 24A is a schematic diagram illustrating in perspective side view an arrangement of a switchable compensated retarder in a privacy angle mode of operation comprising a homeotropically aligned switchable liquid crystal retarder disposed between the first and second passive polar control retarders of plate C; FIGURE 24B and FIGURE 24C are schematic graphs illustrating the variation of output transmission with polar direction for light rays transmitted in the optical stack of FIGURE 24A in a public mode and a privacy mode of operation, respectively; and FIGURE 24D is a schematic graph illustrating the variation in reflectivity with polar direction for light rays reflected from FIGURE 24A in a privacy mode of operation comprising the embodiments illustrated in TABLE 11. Features of the arrangements of FIGURES 24A through 24D not discussed in more detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features. TABLE 11

[0462] The passive polar control retarder 330 comprises first and second C plates 330A, 330B; and the switchable liquid crystal layer 314 is provided between the first and second C plates 330A, 330B. The switchable liquid crystal retarder comprises two surface alignment layers 419a, 419b disposed adjacent to the layer 314 of the liquid crystal material 414 and on opposite sides thereof and each disposed to provide homogeneous alignment in the adjacent liquid crystal material 414. The liquid crystal material layer 414 of the switchable liquid crystal retarder comprises a liquid crystal material 414 having a positive-negative dielectric anisotropy.

[0463] The liquid crystal material layer 314 has a retardance for light of wavelength 550 nm in a range of 500 nm to 1000 nm, preferably in a range of 600 nm to 900 nm and more preferably in a range of 700 nm to 850 nm. The two passive retarders each comprise a passive retarder with an optical axis perpendicular to the plane of the retarder with a total retardance for light of wavelength 550 nm in a range of -300 nm to -700 nm, preferably in a range of -350 nm to -600 nm and more preferably of -400 nm to -500 nm.

[0464] FIGURE 25A is a schematic diagram illustrating in perspective side view a display comprising a switchable compensated retarder disposed between the first and second passive polar control retarder substrates of plate C; and FIGURE 25B is a schematic diagram illustrating in side view part of a display comprising a switchable compensated retarder disposed between the first and second passive polar control retarder substrates of plate C.

[0465] The polar control retarder 300 comprises two passive retarders 330A, 330B and a switchable liquid crystal retarder 301 comprising a layer 314 of liquid crystal material provided between the two passive retarders 330A, 330B. The display device 100 further comprises transmissive electrodes 413, 415 and liquid crystal surface alignment layers 409, 411 formed on one side of each of the two passive retarders 330A, 330B adjacent the switchable liquid crystal retarder layer 314. The display device 100 further comprises first and second substrates between which the switchable liquid crystal retarder layer 314 is provided, the first and second substrates each comprising one of the two passive retarders 330A, 330B.

[0466] Thus, the first C plate 330A has a transparent electrode layer 415 and the liquid crystal alignment layer 411 formed on one side and the second C plate 330B has a transparent electrode layer 413 and the liquid crystal alignment layer 409 formed on one side.

[0467] Liquid crystal layer 314 is provided between first and second substrates 312, 316, and first and second substrates 312, 316 each comprise one of first and second C plates 330A, 330B. The C plates may be provided on double drawn COP films that are coated with ITO to provide electrodes 413, 415 and have liquid crystal alignment layers 409, 411 formed thereon.

[0468] Advantageously, the number of layers may be reduced compared to the arrangement of FIGURE 1, reducing thickness, cost, and complexity. Furthermore, the C plates 330A, 330B may be flexible substrates and may provide a flexible privacy display.

[0469] It would be desirable to provide a liquid crystal layer 314 between the first and second substrates of plate A.

[0470] FIGURE 25C is a schematic diagram illustrating in perspective side view an arrangement of a switchable compensated retarder in a public mode of operation comprising a homogeneously aligned switchable liquid crystal retarder disposed between first and second cross-plate A passive polar control retarders; and FIGURE 25D and FIGURE 25E are schematic graphs illustrating the variation of output transmission with polar direction for light rays transmitted into the structure of FIGURE 25C when actuated in wide-angle and privacy modes of operation, respectively, comprising embodiments further illustrated in TABLE 11. Features of the arrangements of FIGURES 25A through 25E not discussed in further detail may be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0471] The switchable liquid crystal retarder comprises two surface alignment layers 419a, 419b disposed adjacent to layer 314 of liquid crystal material 414 and on opposite sides thereof and each disposed to provide homogeneous alignment in the adjacent liquid crystal material 414. The liquid crystal material layer 414 of the switchable liquid crystal retarder comprises a liquid crystal material 414 having a positive-negative dielectric anisotropy.

[0472] The liquid crystal material layer 314 has a retardance for light of wavelength 550 nm in a range of 500 nm to 1000 nm, preferably in a range of 600 nm to 900 nm and more preferably in a range of 700 nm to 850 nm. Each of the two passive retarders has an optical axis in the plane of the passive retarder, wherein the optical axes are crossed, and each passive retarder of the pair of passive retarders has a retardance for light of wavelength 550 nm in a range of 150 nm to 800 nm, preferably in a range of 200 nm to 700 nm and more preferably in the range of 250 nm to 600 nm.

[0473] In comparison to the arrangement of FIGURE 24A, advantageously plates A can be manufactured at a reduced cost compared to plates C.

[0474] It would be desirable to provide an enhanced image appearance by adding camouflage to the private image viewed by onlooker 47 in the privacy mode of operation.

[0475] FIGURE 26A is a schematic diagram illustrating in perspective side view an arrangement of a switchable retarder in a privacy mode of operation comprising a negative C-plate passive retarder and a homeotropically aligned switchable liquid crystal retarder further comprising a patterned electrode layer 415. At least one of the electrodes 413, 415 may be patterned; in this example, electrode 415 is patterned with regions 415a, 415b, 415c and driven by respective voltage drivers 350a, 350b, 350c with voltages Va, Vb, Vc. Gaps 417 may be provided between the electrode regions 415a, 415b, 415c. The tilt of molecules 414a, 414b, 414c can thus be adjusted independently to reveal a camouflage pattern with different luminance levels for off-axis viewing.

[0476] Thus, the switchable liquid crystal retarder 301 disposed between the reflective polarizer 302 and the additional polarizer 318 is controlled via the addressing electrodes 415a, 415b, 415c and the uniform electrode 413. The addressing electrodes may be patterned to provide at least two pattern regions comprising the electrode 415a and the space 417.

[0477] FIGURE 26B is a schematic diagram illustrating in perspective view the illumination of the front view of a primary viewer and an onlooker by a cloaked luminance-controlled privacy visor. The display 100 may have dark image data 601 and white background data 603 that are visible to the primary viewer 45 in the viewing window 26p. By way of comparison, the onlooker 47 may see the cloaked image as illustrated in FIGURE 26C, which is a schematic diagram illustrating in perspective view the side illumination of an onlooker by a cloaked luminance-controlled privacy visor. Features of the arrangements of FIGURES 26A-26C not discussed in further detail may be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0478] Thus, in the white background regions 603, a camouflage structure may be provided that has mixed luminance of the white region 603. The pattern regions of the electrodes 415a, 415b, 415c are therefore camouflage patterns. At least one of the pattern regions is individually addressable and is arranged to operate in a privacy mode of operation.

[0479] The pattern regions may be arranged to provide camouflage for multiple spatial frequencies by controlling which patterns are provided during the privacy mode of operation. In an illustrative example, a presentation may be provided with text that is 20 mm in height. A camouflage pattern with a similar pattern size may be provided with a first electrode pattern control. In a second example, a photo may be provided with large area content that is more visible to an onlooker 47. The spatial frequency of the camouflage pattern may be reduced to hide the larger area structures by combining the first and second electrode regions to provide the voltage and achieve a resulting lower spatial frequency pattern.

[0480] Advantageously, a controllable cloaking structure may be provided by adjusting the voltages Va, Vb, Vc across layer 892. Substantially no visibility of the cloaking structure may be seen for frontal operation. Furthermore, the cloaking image may be removed, providing Va, Vb, and Vc to be the same.

[0481] In addition to providing camouflage from luminance modulation of the private image, the present embodiments provide camouflaged reflection from ambient lighting 604, advantageously achieving further concealment of private images from onlooker 47 while achieving uncamouflaged reflection for primary user 45.

[0482] The performance of retarders between parallel polarizers when arranged in series will now be described. First, the field of view of a homogeneously aligned liquid crystal retarder 301 will now be described for two different drive voltages.

[0483] FIGURE 27A is a schematic diagram illustrating in perspective side view an arrangement of a homogeneously aligned switchable liquid crystal retarder; FIGURE 27B is a schematic graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 27A for a first applied voltage; and FIGURE 27C is a schematic graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 27A for a second applied voltage that is greater than the first applied voltage, comprising the structure illustrated in TABLE 12.

[0484] FIGURE 27D is a schematic diagram illustrating in perspective side view a plate C disposed between parallel polarizers; and FIGURE 27E is a schematic graph illustrating the variation of output transmission with polar direction for light rays transmitted in FIGURE 27D, comprising the structure illustrated in TABLE 12. TABLE 12

[0485] FIGURE 28A is a schematic diagram illustrating in perspective side view an arrangement of a homogeneously aligned switchable liquid crystal retarder 390 disposed between parallel polarizers 394, 396 in series with a passive field-of-view control retarder comprising a C-plate retarder 392 disposed between parallel polarizers 396, 398; FIGURE 28B is a schematic graph illustrating the variation of output transmission with polar direction for the light rays transmitted in FIGURE 28A for a first applied voltage; FIGURE 28C is a schematic graph illustrating the variation of output transmission with polar direction for the light rays transmitted in FIGURE 28A for a second applied voltage that is greater than the first applied voltage, comprising the structure illustrated in TABLE 12.

[0486] FIGURE 29A is a schematic diagram illustrating in perspective side view an arrangement of a homogeneously aligned switchable liquid crystal retarder in series with a C-plate polar control retarder wherein the homogeneously aligned switchable liquid crystal retarder and the C-plate polar control retarder are disposed between a single pair of parallel polarizers; FIGURE 29B is a schematic graph illustrating the variation of output transmission with polar direction for light rays transmitted in FIGURE 29A for a first applied voltage; and FIGURE 29C is a schematic graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURE 29A for a second applied voltage that is greater than the first applied voltage, comprising the structure illustrated in TABLE 12. The characteristics of the arrangements of FIGURES 27A through 29C not discussed in more detail can be assumed to correspond to the characteristics with equivalent reference numbers as discussed above, including any potential variations in the characteristics.

[0487] Unexpectedly, the ideal conditions for maximum field of view operation are provided by equal and opposite net retardation of polar control retarder 330 compared to switchable liquid crystal retarder layer 314 in its non-driven state. An ideal polar control retarder 330 and switchable liquid crystal retarder layer 314 can achieve (i) no modification of public mode performance from incoming light and (ii) ideal reduction of side viewing angle to off-axis positions for all elevations when arranged to provide a narrow angle state. This teaching can be applied to all display devices disclosed herein.

[0488] It would be desirable to provide further off-axis luminance reduction by directional illumination of the SLM 48. Directional illumination of the SLM 48 by directional backlights 20 will now be described.

[0489] FIGURE 30A is a schematic diagram illustrating in front perspective view a directional backlight 20 (or “narrow angle” or “collimated” backlight), and FIGURE 30B is a schematic diagram illustrating in front perspective view a non-directional backlight 20 (or “narrow angle” or “non-collimated” backlight), either of which may be applied in any of the devices described herein. Thus, a directional backlight 20 as shown in FIGURE 30A provides a narrow cone 450, while a non-directional backlight 20 as shown in FIGURE 30B provides a wide cone of angular distribution 452 of light output rays.

[0490] FIGURE 30C is a schematic graph illustrating variation with luminance with side viewing angle for several different backlight arrangements. The graph of FIGURE 30C may be a cross-section through the polar field of view profiles described herein. Features of the arrangements of FIGURES 30A through 30C not discussed in further detail may be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0491] A Lambertian backlight has a luminance profile 846 that is independent of viewing angle. In the present embodiments, the backlight 20 may be arranged to provide an angular light distribution that has reduced luminance for off-axis viewing positions compared to the front luminance.

[0492] A typical wide-angle backlight has an offset at higher angles such that the full width and half maximum relative luminance may preferably be greater than 40°, more preferably greater than 60°, and most preferably greater than 80°. A typical wide-angle backlight has an offset at higher angles such that the full width and half maximum relative luminance 866 may be greater than 40°, preferably greater than 60°, and most preferably greater than 80°. Furthermore, the relative luminance 864 at +/-45° is preferably greater than 7.5%, more preferably greater than 10%, and most preferably greater than 20%. Advantageously, a display achieving an offset similar to the wide-angle backlight may provide high image visibility to off-axis users.

[0493] Displays comprising wide-angle backlights 20 and only one additional polarizer 318 and polar control retarder 330 (not comprising further polar control retarders 300B and another additional polarizer 318B) typically do not achieve the level of visual safety desirable for off-axis users in the privacy mode of operation. Desirably, such displays may be provided with a directional backlight 20, as will now be described.

[0494] The backlight 20 may be a directional backlight that provides a luminance at polar angles to the line perpendicular to the SLM greater than 45 degrees in at least one azimuthal direction that is at most 30% of the luminance along the line perpendicular to the SLM, preferably at most 20% of the luminance along the line perpendicular to the SLM, and more preferably at most 10% of the luminance along the line perpendicular to the SLM. The directional backlight 20 may have an offset at higher angles such that the maximum width and half-maximum 862 of the relative luminance may be less than 60°, preferably less than 40°, and most preferably less than 20°. In an illustrative example, the luminance 868 at 45 degrees may be 18% of the front luminance of the backlight 20.

[0495] Such luminance profiles may be provided by the directional backlights 20 described below or may also be provided by wide-angle backlights in combination with other additional polarizers 318B and polar control retarders 300B, as described elsewhere in this document.

[0496] A type of switchable backlight 20 will now be described.

[0497] FIGURE 31A is a schematic diagram illustrating in side view a switchable directional display apparatus 100 comprising a switchable liquid crystal polar control retarder 300 and backlight 20. The backlight 20 of FIGURE 31A may be applied in any of the devices described herein and comprising an imaging waveguide 1 illuminated by an array of light sources 15 through an input end 2. FIGURE 31B is a schematic diagram illustrating in perspective rear view an operation of the imaging waveguide 1 of FIGURE 31A in a narrow angle mode of operation.

[0498] Imaging waveguides 1 are of the type described in U.S. Pat. No. 9,519,153, which is incorporated herein by reference in its entirety. Waveguide 1 has an input end 2 extending in a lateral direction along waveguide 1. An array of light sources 15 is disposed along the input end 2 and inputs light into waveguide 1.

[0499] Waveguide 1 also opposed to first and second guiding surfaces 6, 8 extending through waveguide 1 from input end 2 to a reflective end 4 to guide light input to input end 2 back and forth along waveguide 1. Second guiding surface 8 has a plurality of light extraction features 12 facing reflective end 4 and arranged to deflect at least a portion of the light guided back through waveguide 1 from reflective end 4 from different input positions through input end 2 in different directions through first guiding surface 6 that depend on the input position.

[0500] In operation, light rays are directed from light source array 15 through an input end and are guided between first and second guide surfaces 6, 8 without loss to a reflective end 4. The reflected rays are incident on facets 12 and emitted by reflection as light rays 230 or transmitted as light rays 232. The transmitted light rays 232 are directed back through waveguide 1 by facets 803, 805 of rear reflector 800. The operation of rear reflectors is further described in U.S. Pat. No. 10,054,732, which is incorporated herein by reference in its entirety.

[0501] As illustrated in FIGURE 31B, optical power from curved reflective end 4 and facets 12 provides an optical window 26 that is transmitted through SLM 48 and has an axis 197 that is typically aligned with optical axis 199 of waveguide 1. Similar optical window 26 is provided by transmitted light rays 232 that are reflected by rear reflector 800.

[0502] FIGURE 31C is a schematic graph illustrating the field-of-view luminance graph of the output of FIGURE 31B when used in a switchable liquid crystal non-retardant display apparatus. Features of the arrangements of FIGURES 31A through 31C not discussed in more detail can be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0503] Thus, for off-axis viewing, positions observed by onlookers 47 may have reduced luminance, for example, between 1% and 3% of the central peak luminance at a 0 degree elevation and +/- 45 degree lateral angle. Further reduction of off-axis luminance is achieved by the multiple retarders 301, 330 of the present embodiments.

[0504] The backlight 20 may thus further comprise a switchable backlight arranged to switch the output angular luminance profile to provide reduced off-axis luminance in a privacy operating mode and increased off-axis luminance in a public operating mode.

[0505] Another type of directional backlight with low off-axis luminance will now be described.

[0506] FIGURE 32A is a schematic diagram illustrating a side view of a switchable directional display apparatus comprising a backlight 20 including a switchable collimating waveguide 901 and a switchable liquid crystal polar control retarder 300 and an additional polarizer 318. The backlight 20 of FIGURE 32A may be applied to any of the devices described herein and is arranged as follows.

[0507] Waveguide 901 has an input end 902 that extends in a lateral direction along waveguide 901. An array of light sources 915 is disposed along input end 902 and inputs light into waveguide 1. Waveguide 901 also has first and second guiding surfaces 906, 908 that extend through waveguide 1 from input end 2 to a reflective end 4 to guide light input to input end 2 back and forth along waveguide 1. In operation, light is guided between first and second guiding surfaces 906, 908.

[0508] The first guide surface 906 may be provided with a lenticular structure 904 comprising a plurality of elongated lenticular elements 905 and the second guide surface 908 may be provided with prismatic structures 912 that are tilted and act as light extraction features. The plurality of elongated lenticular elements 905 of the lenticular structure 904 and the plurality of tilted light extraction features deflect the input light guided through the waveguide 901 to exit through the first guide surface 906.

[0509] A rear reflector 903 which may be a flat reflector is provided to direct light that is transmitted through surface 908 back through waveguide 901.

[0510] The output light rays that are incident on the prismatic structures 912 and the lenticular elements 905 of the lenticular structure 904 are emitted at angles approaching grazing incidence on the surface 906. A prismatic turning film 926 comprising facets 927 is arranged to redirect the output light rays 234 by total internal reflection through the SLM 48 and compensated switchable liquid crystal polar control retarder 300.

[0511] FIGURE 32B is a schematic diagram illustrating the top view exit of the collimating waveguide 901. Prismatic structures 912 are arranged to provide light at angles of incidence on the lenticular structure 904 that are below the critical angle and therefore can escape. At incidence at the edges of a lenticular surface, the slope of the surface provides a deflection of the light to escape the rays and provides a collimating effect. Light ray 234 may be provided by light rays 188a-c and light rays 189a-c incident at locations 185 of the lenticular structure 904 of the collimated waveguide 901.

[0512] FIGURE 32C is a schematic graph illustrating an iso-luminance field-of-view polar plot for the display apparatus of FIGURE 32A. Thus, a narrow output cone of light can be provided, with size determined by the structures of frames 904, 912 and lathing film 926. Features of the arrangements of FIGURES 32A through 32C not discussed in further detail can be assumed to correspond to features with equivalent reference numbers as discussed above, including any potential variations in the features.

[0513] Advantageously, in regions where bystanders may be located at lateral angles of 45 degrees or greater, for example, the output luminance of the display is small, typically less than 2%. It would be desirable to obtain additional reduction of the output luminance. This additional reduction is provided by the compensated switchable liquid crystal polar control retarder 300 and additional polarizer 318, as illustrated in FIGURE 32A. Advantageously, a high performance privacy display with low off-axis luminance can be provided over a wide field of view.

[0514] Directional backlights, such as the types depicted in FIGURES 31A and FIGURE 32A, in conjunction with the multiple retarders 301, 330 of the present embodiments, can achieve off-axis luminance of less than 1.5%, preferably less than 0.75%, and most preferably less than 0.5% can be achieved for typical onlooker locations 47. Additionally, high on-axis luminance and uniformity can be provided for the primary user 45. Advantageously, a high performance privacy display with low off-axis luminance can be provided over a wide field of view, which can be switched to a public mode by controlling the switchable retarder 301 via the control system 352 illustrated in FIGURE 1A.

[0515] The operation of polar control retarder layers between parallel polarizers for off-axis illumination will now be described further. In the various devices described above, at least one polar control retarder is disposed between reflective polarizer 318 and additional polarizer 218 in various different configurations. In each case, the at least one polar control retarder is configured so that it does not affect the luminance of light passing through the reflective polarizer 318, the at least one polar control retarder, and the additional polarizer 218 along an axis along a line perpendicular to the plane of the polar control retarder (or retarders), but reduces the luminance of light passing through the reflective polarizer 318, the at least one polar control retarder, and the additional polarizer 218 along an axis inclined to a line perpendicular to the plane of the polar control retarder (or retarders), in at least one of the switchable states of the compensated switchable polar control retarder 300. A description of this effect will now be given in more detail, the principles of which can be applied in general to all of the devices described above.

[0516] FIGURE 33A is a schematic diagram illustrating in perspective view the illumination of a polar control retarder layer by off-axis light. The polar control retarder 630 may comprise birefringent material, represented by refractive index ellipsoid 632 with optical axis direction 634 at 0 degrees relative to the x-axis, and have a thickness 631. Features of the arrangements of FIGURES 33A through 35E below that are not discussed in further detail may be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0517] Normal light rays 636 propagate so that the path length in the material is the same as the thickness 631. Light rays 637 that are in the y-z plane have an increased path length; however, the birefringence of the material is substantially the same as rays 636. By way of comparison, light rays 638 that are in the x-z plane have an increased path length in the birefringent material, and furthermore, the birefringence is different from that of normal ray 636.

[0518] The retardation of the polar control retarder 630 is therefore dependent on the angle of incidence of the respective ray, and also on the plane of incidence, i.e. rays 638 in the x-z plane will have a different retardation than normal rays 636 and rays 637 in the y-z plane.

[0519] The interaction of polarized light with the polar control retarder 630 will now be described. To distinguish from the first and second polarization components during operation in a directional backlight 101, the following explanation refers to the third and fourth polarization components.

[0520] FIGURE 33B is a schematic diagram illustrating in perspective view the illumination of a polar control retarder layer by off-axis light from a third linear polarization state at 90 degrees to the x-axis, and FIGURE 33C is a schematic diagram illustrating in perspective view the illumination of a polar control retarder layer by off-axis light from a fourth linear polarization state at 0 degrees to the x-axis. In such arrangements, the incident linear polarization states are aligned with the optical axes of the birefringent material, represented by ellipse 632. Accordingly, no phase difference between the third and fourth orthogonal polarization components is provided, and there is no resulting change in the polarization state of the linearly polarized input for each ray 636, 637, 638. Thus, polar control retarder 630 introduces no phase shift in the polarization components of light passed through the polarizer on the input side of polar control retarder 630 along an axis along a line perpendicular to the plane of polar control retarder 630. Accordingly, polar control retarder 630 does not affect the luminance of light passing through polar control retarder 630 and the polarizers (not shown) on either side of polar control retarder 630. Although FIGURES 29A-29C specifically refer to polar control retarder 630 which is passive, a similar effect is achieved by the polar control retarders in the devices described above.

[0521] FIGURE 33D is a schematic diagram illustrating in perspective view the illumination of a polar control retarder layer 630 by off-axis light from a 45 degree linear polarization state. The linear polarization state may be resolved into third and fourth polarization components that are respectively orthogonal and parallel to the direction of the optical axis 634. The thickness of the polar control retarder 631 and the retardance of the material represented by the refractive index ellipsoid 632 may provide a net effect of relatively shifting the phase of the third and fourth polarization components incident thereon in a perpendicular line direction represented by the ray 636 by one-half wavelength, to a design wavelength. The design wavelength may, for example, be in the range of 500 to 550 nm.

[0522] At the design wavelength and for light propagating normally along beam 636, the output polarization may be rotated by 90 degrees to a linear polarization state 640 at -45 degrees. Light propagating along beam 637 may see a phase difference that is similar, but not identical, to the phase difference along beam 637 due to the change in thickness, and therefore an elliptical polarization state 639 may be emitted which may have a principal axis similar to the linear polarization axis of the light output from beam 636.

[0523] By way of contrast, the phase difference for the incident linear polarization state along beam 638 may be significantly different, in particular a lower phase difference may be provided. Such a phase difference may provide an output polarization state 644 that is substantially circular at a given tilt angle 642. Thus, polar control retarder 630 introduces a phase shift to the polarization components of light passed through the polarizer on the input side of polar control retarder 630 along an axis corresponding to beam 638 that is tilted to a line perpendicular to the plane of polar control retarder 630. Although FIGURE 29D refers to polar control retarder 630 that is passive, a similar effect is achieved by the polar control retarders described above, in a switchable state of the liquid crystal switchable polar control retarder corresponding to the privacy mode.

[0524] To illustrate the off-axis behavior of polar control retarder stacks, the angular luminance control of C plates 330A, 330B between an additional polarizer 318 and output display polarizer 218 will now be described for various off-axis lighting arrangements with reference to the operation of a C plate between parallel polarizers 500, 210.

[0525] FIGURE 34A is a schematic diagram illustrating in perspective view the illumination of a plate layer C by off-axis polarized light having a positive elevation. The incident linear polarization component 704 is incident on the birefringent material 632 of the polar control retarder 560 which is a plate C with optical axis direction 507 that is perpendicular to the plane of the polar control retarder 560. The polarization component 704 sees no net phase difference in transmission through the liquid crystal molecule and therefore the output polarization component is the same as component 704. Thus, maximum transmission is seen through the polarizer 210. Thus, the polar control retarder 560 having an optical axis 561 perpendicular to the plane of the polar control retarder 560 which is the x-y plane. The polar control retarder 560 having an optical axis perpendicular to the plane of the polar control retarder comprises a plate C.

[0526] FIGURE 34B is a schematic diagram illustrating in perspective view the illumination of a plate layer C by off-axis polarized light having a negative lateral angle. As in the arrangement of FIGURE 34A, the polarization state 704 sees no net phase difference and is transmitted with maximum luminance. Thus, polar control retarder 560 does not introduce phase shift in the polarization components of light passed through the polarizer on the input side of polar control retarder 560 along an axis along a line perpendicular to the plane of polar control retarder 560. Accordingly, polar control retarder 560 does not affect the luminance of light passing through polar control retarder 560 and the polarizers (not shown) on either side of polar control retarder 560. Although FIGURES 29A-29C refer specifically to polar control retarder 560 that is passive, a similar effect is achieved by the polar control retarders in the devices described above.

[0527] FIGURE 34C is a schematic diagram illustrating in perspective view the illumination of a plate layer C by off-axis polarized light having a positive elevation and negative lateral angle. In comparison to the arrangement of FIGURES 34A and 34B, the polarization state 704 is resolved into eigenstates 703, 705 with respect to the birefringent material 632, providing a net phase difference in transmission through the polar control retarder 560. The resulting elliptical polarization component 656 is transmitted through the polarizer 210 with reduced luminance compared to the rays illustrated in FIGURES 34A and 34B.

[0528] FIGURE 34D is a schematic diagram illustrating in perspective view the illumination of a plate layer C by off-axis polarized light having a positive elevation and positive lateral angle. In a manner similar to FIGURE 34C, polarization component 704 is resolved into eigenstates 703, 705 which undergo a net phase difference, and elliptical polarization component 660 is provided which upon transmission through the polarizer reduces the luminance of the respective off-axis ray. Thus, the polar control retarder 560 introduces a phase shift to the polarization components of the light passed through the polarizer at the input side of the polar control retarder 560 along an axis that is inclined to a line perpendicular to the plane of the polar control retarder 560. Although FIGURE 29D refers to the polar control retarder 560 that is passive, a similar effect is achieved by the polar control retarders described above in a switchable state of the liquid crystal switchable polar control retarder corresponding to the privacy mode.

[0529] FIGURE 34E is a schematic graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURES 34A through 34D. Thus, plate C can provide luminance reduction in polar quadrants. In combination with the switchable liquid crystal layer 314 described elsewhere herein, (i) removal of luminance reduction from plate C can be provided in a first wide-angle state of operation (ii) the extended polar region for luminance reduction can be achieved in a second privacy state of operation.

[0530] To illustrate the off-axis behavior of the polar control retarder stacks, the angular luminance control of the crossed A plates 330A, 330B between an additional polarizer 318 and the output display polarizer 218 will now be described for various off-axis lighting arrangements.

[0531] FIGURE 35A is a schematic diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a positive elevation. Linear polarizer 218 with electric vector transmission direction 219 is used to provide a linear polarization state 704 that is parallel to the lateral direction on the first A plate 330A of the cross-plates A 330A, 330B. The optical axis direction 331A is tilted by +45 degrees relative to the lateral direction. Retarding the polar control retarder 330A to the off-axis angle θi in the positive elevation direction provides a resultant polarization component 650 that is generally elliptical at the output. The polarization component 650 is incident on the second plate A 330B of the crossed plates A 330A, 330B having an optical axis direction 33iB that is orthogonal to the optical axis direction 33iA of the first plate A 330A. In the plane of incidence of FIGURE 35A, the retardance of the second plate A 330B for the off-axis angle θi is equal and opposite to the retardance of the first plate A 330A. Thus, a net zero retardance is provided for the incident polarization component 704 and the output polarization component is the same as the input polarization component 704.

[0532] The output polarization component is aligned with the electric vector transmission direction of the additional polarizer 318 and is therefore transmitted efficiently. Advantageously, substantially no loss is provided for light rays having zero lateral angle angular component, so that full transmission efficiency is achieved.

[0533] FIGURE 35B is a schematic diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a negative lateral angle. Thus, the input polarization component is converted by the first A plate 330A to an intermediate polarization component 652 which is generally an elliptical polarization state. The second A plate 330B again provides equal and opposite retardation to the first A plate, so that the output polarization component is the same as the input polarization component 704 and light is efficiently transmitted through the polarizer 318.

[0534] Thus, the polar control retarder comprises a pair of retarders 330A, 330B having optical axes in the plane of the retarders 330A, 330B that are crossed, which is the x-y plane in the present embodiments. The pair of retarders 330A, 330B have optical axes 331A, 331B that each extend 45° to an electric vector transmission direction that is parallel to the electric vector transmission of the polarizer 318.

[0535] Advantageously, substantially no loss is provided for light rays having zero elevation angular component, so that full transmission efficiency is achieved.

[0536] FIGURE 35C is a schematic diagram illustrating in perspective view the illumination of retarder layers of cross-plate A by off-axis polarized light having a positive elevation and negative lateral angle. Polarization component 704 is converted to an elliptical polarization component 654 by first plate A 330A. A resulting elliptical component 656 is emitted from second plate A 330B. Elliptical component 656 is analyzed by input polarizer 318 with reduced luminance compared to the input luminance of first polarization component 704.

[0537] FIGURE 35D is a schematic diagram illustrating in perspective view the illumination of cross-plate A retarder layers by off-axis polarized light having a positive elevation and positive lateral angle. The polarization components 658 and 660 are provided by the first and second A plates 330A, 330B since the net retardance of the first and second retarders does not provide compensation.

[0538] Thus, luminance is reduced for light rays that have non-zero lateral angle and non-zero elevation components. Advantageously, display privacy can be increased for onlookers arranged in the viewing quadrants while luminous efficiency for users of the primary display is not substantially reduced.

[0539] FIGURE 35E is a schematic graph illustrating the variation of output transmission with polar direction for the transmitted light rays in FIGURES 35A through 35D. Compared to the arrangement of FIGURE 34E, the luminance reduction area is increased for off-axis viewing. However, the switchable liquid crystal layer 314 may provide reduced uniformity compared to the C plate arrangements for off-axis viewing in the first public mode operating state.

[0540] As used herein, the terms “substantially” and “approximately” provide an industry-accepted tolerance for its corresponding term and/or inter-item relativity. This industry-accepted tolerance ranges from zero to ten percent and corresponds to, but is not limited to, component values, angles, etc. This inter-item relativity ranges from approximately zero to ten percent.

[0541] Although various embodiments in accordance with the principles disclosed herein have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. Accordingly, the breadth and scope of this disclosure are not to be limited by any of the exemplary embodiments described above, but are to be defined solely in accordance with any claims and their equivalents arising from this disclosure. Furthermore, the above advantages and features are provided in the embodiments described, but are not to limit the application of such claims to processes and structures that realize any or all of the above advantages. Furthermore, section headings in this document are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational suggestions. Such headings are not to limit or characterize the embodiments set forth in any claims that may arise from this disclosure. Specifically and by way of example, although the headings refer to a “Field of the Art,” the claims are not to be limited by the language chosen under that heading to describe the so-called field. Furthermore, a description of a technology in the “Background” should not be construed as an admission that such technology is prior art to any embodiment (or embodiments) in this disclosure. Nor should the “Summary” be construed as a characterization of the embodiment (or embodiments) set forth in the claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple embodiments may be established within the limitations of the multiple claims arising from this disclosure, and such claims adequately define the embodiment (or embodiments) and their equivalents that are protected by it. In all cases, the scope of such claims should be considered on their own merits in light of this disclosure, but should not be limited by the headings set forth herein.

Claims (58)

1. A display device for use in ambient lighting, comprising: a spatial light modulator (SLM) arranged to emit light; wherein the SLM comprises an output polarizer disposed on the output side of the SLM, the output polarizer being a linear polarizer; an additional polarizer disposed on the output side of the output polarizer, the additional polarizer being a linear polarizer; a reflective polarizer disposed between the output polarizer and the additional polarizer, the reflective polarizer being a linear polarizer; and a plurality of polar control retarders disposed between the reflective polarizer and the additional polarizer, wherein there are no additional polarizers between the reflective polarizer and the additional polarizer, wherein the plurality of polar control retarders comprises a switchable liquid crystal retarder comprising a layer of liquid crystal material and at least one polar control retarder. 2. The display device of claim 1, wherein the plurality of polar control retarders are arranged, in a switchable state of the switchable liquid crystal retarder, simultaneously to introduce no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along a first axis and to introduce a net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along a second axis inclined at a different angle relative to the first axis. 3. The display device of claim 2, wherein the at least one passive polar control retarder is arranged to introduce no net relative phase shift in the orthogonal polarization components of the light passed through the reflective polarizer along a third geometric axis and to introduce a net relative phase shift in the orthogonal polarization components of the light passed through the reflective polarizer along a fourth geometric axis inclined at an angle different from the third geometric axis. 4. The display device of claim 2 or 3, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent the liquid crystal material layer on opposite sides thereof and each disposed to provide homeotropic alignment in the liquid crystal material layer. 5. The display device of claim 4, wherein the liquid crystal material layer of the switchable liquid crystal retarder comprises a liquid crystal material having a negative dielectric anisotropy. 6. Display device according to claim 4 or 5, characterized in that the liquid crystal material layer has a retardance for light of wavelength 550 nm in a range of 500 nm to 1,000 nm. 7. The display device of any one of claims 4 to 6, wherein: the at least one passive polar control retarder comprises a passive retarder having an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardance for light of a wavelength of 550 nm in a range of -300 nm to -900 nm; or the at least one passive polar control retarder comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the pair of passive polar control retarders has a retardance for light of a wavelength of 550 nm in a range of 300 nm to 800 nm. 8. The display device of claim 2 or 3, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to the liquid crystal material layer and on opposite sides and each disposed to provide homogeneous alignment in the liquid crystal material layer. 9. The display device of claim 8, wherein the liquid crystal material layer of the switchable liquid crystal retarder comprises a liquid crystal material having a positive dielectric anisotropy. 10. The display device of claim 8 or 9, wherein the liquid crystal material layer has a retardance for light of wavelength 550 nm in a range of 500 nm to 900 nm. 11. A display device according to any one of claims 8 to 10, wherein: the at least one passive polar control retarder comprises a passive retarder having an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardation for light of a wavelength of 550 nm in a range of -300 nm to -700 nm; or the at least one passive polar control retarder comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, wherein each passive retarder of the pair of passive retarders has a retardation for light of a wavelength of 550 nm in a range of 300 nm to 800 nm. 12. The display device of claim 2 or 3, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to and on opposite sides of the liquid crystal material layer, wherein one of the surface alignment layers is disposed to provide homeotropic alignment in the liquid crystal material and the other of the surface alignment layers is disposed to provide homogeneous alignment in at least part of the liquid crystal material. 13. The display device of claim 12, wherein the surface alignment layer arranged to provide homogeneous alignment is between the liquid crystal material layer and the polar control retarder; the liquid crystal material layer has a retardance for light of a wavelength of 550 nm in a range of 700 nm to 2,000 nm; and the at least one passive polar control retarder comprises a passive retarder having its optical axis perpendicular to the plane of the retarder, the at least one passive polar control retarder having a retardance for light of a wavelength of 550 nm in a range of -400 nm to -1,800 nm; or the at least one passive polar control retarder comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, each retarder of the retarder pair having a retardance for light of wavelength 550 nm in a range of 400 nm to 1,800 nm. 14. The display device of claim 12, wherein the surface alignment layer arranged to provide homeotropic alignment is between the liquid crystal material layer and the polar control retarder; the liquid crystal material layer has a retardance for light of a wavelength of 550 nm in a range of 500 nm to 1800 nm; and the at least one passive polar control retarder comprises a passive retarder having its optical axis perpendicular to the plane of the retarder, the at least one passive polar control retarder having a retardance for light of a wavelength of 550 nm in a range of -300 nm to -1600 nm; or the at least one passive polar control retarder comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed, each retarder of the pair of retarders having a retardance for light of wavelength 550 nm in a range of 400 nm to 1,600 nm. 15. The display device of any one of claims 2 to 14, wherein each alignment layer has a pre-tilt with a pre-tilt direction with a component in the plane of the liquid crystal material layer that is parallel or antiparallel or orthogonal to the electric vector transmission direction of the reflective polarizer. 16. Display device according to any one of claims 2 to 15, characterized in that the at least one polar control retarder further comprises two passive retarders, wherein the switchable liquid crystal retarder is provided between the two passive retarders. 17. The display device of claim 16, further comprising a transmissive electrode and a liquid crystal surface alignment layer formed on one side of each of two passive retarders adjacent to the switchable liquid crystal retarder. 18. The display device of claim 16 or 17, further comprising first and second substrates between which the switchable liquid crystal retarder is provided, the first and second substrates each comprising one of the two passive retarders. 19. Display device according to any one of claims 16 to 18, characterized in that the two passive retarders each comprise a passive retarder with an optical axis perpendicular to the plane of the retarder with a total retardation for light of wavelength 550 nm in a range of -300 nm to -700 nm. 20. Display device according to any one of claims 16 to 19, characterized in that each of the two passive retarders has an optical axis in the plane of the passive retarder, wherein the optical axes are crossed, and each passive retarder of the pair of passive retarders has a retarder for light of wavelength 550 nm in a range of 150 nm to 800 nm. 21. The display device of any one of claims 2 to 20, wherein the switchable liquid crystal retarder further comprises transmissive electrodes arranged to apply a voltage to control the liquid crystal material layer. 22. The display device of claim 21, wherein the transmissive electrodes are on opposite sides of the liquid crystal material layer. 23. The display device of claim 21 or 22, wherein the transmissive electrodes are shaped to provide at least two pattern regions. 24. The display device of any one of claims 21 to 23, further comprising a control system arranged to control the voltage applied across the transmissive electrodes of the switchable liquid crystal retarder. 25. The display device of any preceding claim, wherein the at least one polar control retarder comprises at least one passive polar control retarder that is arranged to introduce no net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis along a line perpendicular to the plane of the at least one passive polar control retarder and to introduce a net relative phase shift to orthogonal polarization components of light passed through the reflective polarizer along an axis inclined to a line perpendicular to the plane of the at least one passive polar control retarder. 26. The display device of claim 25, wherein the at least one passive polar control retarder comprises at least two passive retarders with at least two different orientations of optical axes. 27. The display device of claim 25 or 26, wherein the at least one passive polar control retarder comprises a passive retarder having an optical axis perpendicular to the plane of the retarder. 28. Display device according to any one of claims 25 to 27, characterized in that the at least one passive polar control retarder comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed. 29. The display device of claim 28, wherein the pair of retarders has optical axes that extend 45° and 135°, respectively, relative to an electrical vector transmission direction of the output polarizer. 30. Display device according to claim 28 or 29, characterized in that the at least one passive polar control retarder further comprises an additional pair of passive retarders arranged between the first-mentioned pair of passive retarders and having optical axes in the plane of the passive retarders that are crossed. 31. The display device of claim 30, wherein the additional pair of passive retarders has optical axes that extend at 0° and 90°, respectively, relative to an electrical vector transmission direction that is parallel to the electrical vector transmission of the output polarizer. 32. The display device of any one of claims 25 to 31, wherein the at least one passive polar control retarder comprises a passive retarder with an optical axis that is oriented with a component perpendicular to the plane of the retarder and a component in the plane of the retarder. 33. The display device of claim 32, wherein the in-plane component of the passive retarder extends at 0° relative to an electric vector transmission direction parallel or perpendicular to the electric vector transmission of the output polarizer. 34. The display device of claim 32 or 33, wherein the at least one passive polar control retarder further comprises a passive retarder having an optical axis perpendicular to the plane of the passive retarder or a pair of passive retarders having optical axes in the plane of the crossed passive retarders. 35. The display device of any one of claims 1 to 34, further comprising at least one other polar control retarder disposed between the output polarizer and the reflective polarizer. 36. The display device of claim 35, wherein a further polarizer is disposed between the at least one further polar control retarder and the reflective polarizer. 37. The display device of claim 35 or 36, wherein the at least one first-mentioned polar control retarder comprises a first switchable liquid crystal retarder comprising a first layer of liquid crystal material, and the at least one other polar control retarder comprises a second switchable liquid crystal retarder comprising a second layer of liquid crystal material. 38. The display device of claim 37, wherein the first and second liquid crystal retarders have different retardances. 39. The display device of claim 38, further comprising a control system arranged to control the application of a common voltage across the first and second switchable liquid crystal retarders, and wherein the first liquid crystal material of the first liquid crystal retarder is different from the second liquid crystal material of the second liquid crystal retarder. 40. The display device of any one of claims 37 to 39, wherein the first and second liquid crystal material layers of each of the first and second switchable liquid crystal retardants have a retardation for light of a wavelength of 550 nm in a range of 450 nm to 850 nm. 41. The display device of any one of claims 37 to 40, wherein: the at least one first-mentioned polar control retarder further comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer; the at least one further polar control retarder comprises a further pair of passive retarders having optical axes in the plane of the further retarders that are crossed and extend at 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer; and the optical axes of the one of the first-mentioned pair of passive retarders and the one of the other pair of passive retarders closest to each other extend in the same direction. 42. The display device of claim 41, wherein each passive retarder of the first-mentioned pair of passive retarders and each passive retarder of the other pair of passive retarders has a retardance for light of a wavelength of 550 nm in a range of 300 nm to 800 nm. 43. Display device according to any one of claims 35 to 40, characterized in that the at least one further polar control retarder comprises at least one additional passive retarder. 44. The display device of any one of claims 1 to 34, further comprising: a backlight arranged to emit light, wherein the SLM is a transmissive SLM arranged to receive output light from the backlight, and the SLM further comprises an input polarizer disposed on the input side of the SLM, the input polarizer being a linear polarizer; and an additional polarizer disposed on the input side of the input polarizer, the additional polarizer being a linear polarizer; and at least one other polar control retarder disposed between the additional polarizer and the input polarizer. 45. The display device of claim 44, wherein the at least one first-mentioned polar control retarder comprises a first switchable liquid crystal retarder comprising a first layer of liquid crystal material, and the at least one other polar control retarder comprises a second switchable liquid crystal retarder comprising a second layer of liquid crystal material. 46. The display device of claim 45, wherein the first and second liquid crystal retarders have different retardances. 47. The display device of claim 46, further comprising a control system arranged to control the application of a common voltage across the first and second switchable liquid crystal retarders, and wherein the first liquid crystal material of the first liquid crystal retarder is different from the second liquid crystal material of the second liquid crystal retarder. 48. The display device of any one of claims 45 to 47, wherein the first and second liquid crystal material layers of each of the first and second switchable liquid crystal retardants have a retardation for light of a wavelength of 550 nm in a range of 450 nm to 850 nm. 49. The display device of any one of claims 45 to 48, wherein: the at least one first-mentioned polar control retarder further comprises a pair of passive retarders having optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer; the at least one other polar control retarder comprises a further pair of passive retarders having optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, relative to an electric vector transmission direction of the output polarizer; and the optical axes of the one of the first-mentioned pair of passive retarders and the one of the other pair of passive retarders closest to each other extend in the same direction. 50. The display device of claim 49, wherein each passive retarder of the first-mentioned pair of passive retarders and each passive retarder of the other pair of passive retarders has a retardance for light of a wavelength of 550 nm in a range of 300 nm to 800 nm. 51. The display device of any one of claims 44 to 50, wherein the at least one other polar control retarder comprises at least one other passive retarder. 52. The display device of claim 1, further comprising: a backlight arranged to emit light, the SLM being a transmissive SLM arranged to receive light output from the backlight, wherein the backlight provides a luminance at polar angles to the line perpendicular to the SLM greater than 45 degrees that is at most 30% of the luminance along the line perpendicular to the SLM. 53. Display device according to any one of claims 1 to 52, characterized in that the SLM is an emissive SLM. 54. The display device of any one of claims 1 to 53, wherein the reflective polarizer and the output polarizer have parallel electric vector transmission directions. 55. Display device according to any one of claims 1 to 54, characterized in that the reflective polarizer and the additional polarizer have parallel electric vector transmission directions. 56. The display device of any one of claims 1 to 55, wherein the reflective polarizer and the additional polarizer have electrical vector transmission directions that are not parallel, and the display device further comprises a rotator retarder disposed between the reflective polarizer and the additional polarizer, the rotator retarder being arranged to rotate a polarization direction of polarized light incident thereon between electrical vector transmission directions of the output polarizer and the additional polarizer. 57. A viewing angle control optical element for application on the output side of a display device for use in ambient lighting comprising a spatial light modulator (SLM) arranged to emit light; wherein the SLM comprises an output polarizer disposed on the output side of the SLM; the viewing angle control optical element comprising: an additional polarizer; a reflective polarizer disposed between the output polarizer and the additional polarizer in applying the viewing angle control optical element to the display device; and a plurality of polar control retarders disposed between the reflective polarizer and the additional polarizer, wherein there are no additional polarizers between the reflective polarizer and the additional polarizer, wherein the plurality of polar control retarders comprises a switchable liquid crystal retarder comprising a layer of liquid crystal material, and at least one passive polar control retarder. 58. The viewing angle control optical element of claim 57, wherein the plurality of polar control retarders are arranged, in a switchable state of the switchable liquid crystal retarder, simultaneously to introduce no net relative phase shift in the orthogonal polarization components of light passed through the reflective polarizer along a first axis and to introduce a net relative phase shift in the orthogonal polarization components of light passed through the reflective polarizer along a second axis inclined at a different angle to the first axis.