GB2584416A

GB2584416A - Integrated privacy windows for liquid crystal displays

Info

Publication number: GB2584416A
Application number: GB1907252.9A
Authority: GB
Inventors: Too Patrick; Cain Paul
Original assignee: FlexEnable Ltd
Current assignee: FlexEnable Ltd
Priority date: 2019-05-23
Filing date: 2019-05-23
Publication date: 2020-12-09
Also published as: GB201907252D0; WO2020234393A1; TW202102907A

Abstract

The device comprises a first quarter waveplate,105, a second quarter waveplate, 110, above the first quarter waveplate and a first polariser, 115, above the second quarter waveplate. The first quarter waveplate is configured to receive a polarised light source (from top polariser, 120) which has a polarisation axis that is substantial perpendicular to a polarisation axis of the first polariser. The first quarter waveplate and the second quarter waveplate are configured to be switchable between a first configuration and a second configuration. In the first configuration the quarter waveplates comprise a pattern of alternating regions (such as stripes or a checkboard pattern) in the second configuration the quarter waveplates comprise an un-patterned zone. The alternating regions in the first configuration comprise first regions that alter the polarisation of light and second regions that do not alter the polarisation of light. The patterns on the first and second quarter waveplates are aligned so that normally incident light from the polarised light source will pass through the first, polarising regions, of the first quarter waveplate and the second, un-polarising regions of the second quarter waveplate and vice versa.

Description

Integrated Privacy Windows for Liquid Crystal Displays

Technical Field of the Disclosure

This disclosure relates to privacy screens, particularly but not exclusively, switchable privacy screens that may be integrated in a display.

Background to the Disclosure

Privacy screens can be used to block unwanted viewers from viewing a display, by decreasing the viewing angle of a monitor, preventing it from being viewed from the side. Conventional privacy screens are usually either manually mounted in front of an LCD or they are permanently built-in to the LCD and cannot be temporary disabled.

US 6,239,853 describes a privacy screen according to the state-of-the-art. This privacy screen is formed on glass, and is not switchable. Thick glass makes the whole product heavy and thicker. A thick glass substrate would also absorb some of the light, reducing the viewing performance of the device.

US 2018/0210243 describes a further state-of-the-art privacy screen that uses a scattering layer to deflect light. US 2013/0162924 describes a further state-of-the-art privacy screen that requires a chromonics layer and liquid dye. In the private mode this device is in a white state, emitting bright light. This uses a lot of power.

A privacy screen with a white image as the private mode is not very appealing and consumes more energy as the backlight needs to be made brighter. State-of-the-art privacy screens operating with white light as private mode are very conspicuous, notifying those around the user that the computer is on. This is not friendly for neighbours, for instance on an aircraft at night.

Summary

According to a first aspect of the disclosure, there is provided a device for reversibly reducing a viewing angle, the device comprising: a first quarter waveplate; a second quarter waveplate above the first quarter waveplate; a first polariser above the second quarter waveplate; wherein the first quarter waveplate is configured to receive a polarised light source, wherein a polarisation axis of the first polariser is configured to be perpendicular to a polarisation axis of the polarised light source; wherein the first quarter waveplate and the second quarter waveplate are configured to be switchable between a first configuration and a second configuration; wherein in the first configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one activated zone; and wherein in the second configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one non-activated zone.

The device may be a device for reversibly reducing the viewing angle of the polarised light source.

In the first configuration the at least one activated zone may comprise a patterned waveplate zone, and in the second configuration the at least one non-activated zone may comprise an unpatterned waveplate zone. A patterned waveplate zone herein refers to a portion of the waveplate that has regions acting as a waveplate, and regions acting as a pass-through. These regions may form a pattern. The pattern may be stripes, checkerboard, spots, hexagonal pattern, or any other 2D pattern.

In the first configuration each activated zone may comprise a striped patterned waveplate zone, and the striped patterned waveplate zone may comprise an alternating pattern of stripes. The striped patterned waveplate zone may comprise horizontal stripes, vertical stripes, or diagonal stripes. Horizontal stripes block viewers from wide vertical viewing angles, and vertical stripes block viewers from wide horizontal viewing angles.

In the first configuration each activated zone may comprise a checkerboard patterned waveplate zone, and the checkerboard patterned waveplate zone may comprise an alternating pattern of squares. The checkerboard patterned waveplate zone blocks viewers from wide vertical viewing angles and wide horizontal viewing angles.

The checkerboard patterned waveplate zone may comprise a pattern of crossed horizontal lines and vertical lines to form alternating squares.

In the first configuration each patterned waveplate zone may comprise: a first plurality of regions configured to alter the polarisation of light passing through the first plurality of regions of the patterned waveplate zone; and a second plurality of regions configured to allow light to pass through the second plurality of regions of the patterned waveplate zone without altering the polarisation of the light. In other words the first plurality of regions is configuration to transmit light incident on the first plurality of regions with a define dangle of rotations, and the second plurality of regions is configured to transmit light incident on the second plurality of regions without rotation.

In the first configuration the first plurality of regions of the first waveplate are aligned with the second plurality of regions of the second waveplate. This means that light normally incident on the device either passes through one of the first plurality of regions of the first waveplate and one of the second plurality of regions of the second waveplate, or one of the second plurality of regions of the first waveplate and one of the first plurality of regions of the second waveplate. Light normally incident on the device would not pass through one of the first plurality of regions of both waveplates, or would not pass through one of the second plurality of regions of both waveplates.

The second waveplate may be positioned such that normally incident light passing through the first plurality of regions of the first waveplate will pass through one of the second plurality of regions of the second waveplate, and normally incident light passing through the second plurality of regions of the first waveplate will pass through one of the first plurality of regions of the second waveplate.

In the second configuration, one of the first waveplate or the second waveplate may be configured to alter the polarisation of light passing through the at least one non-activated zone of the one of the first waveplate or the second waveplate, and the other of the first waveplate or the second waveplate may be configured to allow light to pass through the at least one non-activated zone of the other of the first waveplate or the second waveplate without altering the polarisation of the light. In other words, one of the waveplates may act as a blanket waveplate, and the other waveplate may act as a blanket pass-through.

Each of the first waveplate and the second waveplate may be configured to alter the polarisation of light by 90°, when acting as waveplates.

In the first configuration the device may be configured to block light from the polarised light source from an angle greater than 30° to a normal through the device from passing through the device. Alternatively the device may block light from the polarised light source from angles less than 30° or greater than 30°, to provide an even further reduced or less reduced viewing angle. This is dependent upon the distance between waveplates, and the geometry of the waveplates.

In the second configuration the device may be configured to allow light from the polarised light source from an angle greater than 30° to a normal through the device from passing through the device. In normal mode, the device may allow light from all angles to pass through the device.

The first waveplate and the second waveplate may be separated by a predetermined distance, C. In the first configuration each of the first plurality of regions may have a predetermined width of value S1, and in the first configuration each of the second plurality of regions may have a predetermined width of value 52. Si and S2 may be substantially equal.

The ratio of C:51 may be approximately 2:1. This ratio allows a threshold viewing angle of 30° when the device is in privacy mode.

The device may further comprise a polarised light source. Alternatively, the device may be manufactured and supplied without a polarised light source, and used with a separate polarised light source.

The polarised light source may comprise a display. The display may be an LCD, an OLED display, a plasma display, TFT display, or other types of display. The display may be a display that emits polarised light. The display may be integrated with the first and second waveplates and the first polariser in a single display unit. The display may comprise a backlight, a bottom polariser, a top polariser, and a LCD cell. The top polariser may have a polarisation axis perpendicular to the polarisation axis of the first polariser, so that the display provides polarised light to the waveplates that has an axis of polarisation perpendicular to the axis of polarisation of the first polariser.

The device may further comprise a second polariser, and the first quarter waveplate may be above the second polariser, and a polarisation axis of the second polariser may be perpendicular to a polarisation axis of the first polariser. The device may be provided with a second polariser, and without a source of polarised light. The device may then be used on other applications such as windows, or mirrors.

Each of the first quarter waveplate and the second quarter waveplate may comprise: two electrode layers; two alignment layers between the electrode layers; and a liquid crystal layer between the alignment layers. The waveplates may comprise spacers or pillars between the electrode layers in order to space the electrode layers from each other.

The electrodes layers may be configured such that when the electrode layers are in a powered state the device is in the first configuration, and when the electrode layers are in an unpowered state the device is in the second configuration.

For each of the first quarter waveplate and the second quarter waveplate, at least one of the two electrode layers may be formed on a plastic substrate. One or both of the electrode layers within each waveplate may be formed on plastic substrate. The plastic substrate may be a thin plastic substrate and/or a flexible plastic substrate. This allows the separation between waveplates, C, to be minimised in comparison to state-of-the-art devices. This improves the performance of the device. Minimising C allows the whole product to be thinner and lighter than compared to a glass based privacy screen. Further, controlling C also allows the viewing angle to be controlled. As plastic is thinner, C can be smaller and the threshold viewing angle can be wider.

The electrode layers may comprise a plurality of laterally spaced electrodes. The electrodes of one electrode layer within a waveplate may be aligned with the electrodes of the other electrode layer within the waveplate. When a voltage is applied, the electrodes may alter the LC between the alignment layers such that it either acts as a waveplate and rotates the polarisation of light, or acts as a pass through and allows light through unaffected.

In the first configuration the electrodes may be aligned with the regions of the waveplates acting as a waveplate, or the regions of the display acting as a pass through. The electrodes of one waveplate may be aligned with regions acting as a waveplate and the electrodes of the other waveplate may be aligned with the regions of the waveplate acting as a pass-through.

According to a further aspect of the disclosure, there is provided an eyewear apparatus, the eyewear apparatus comprising a device as disclosed above. The eyewear apparatus may be configured to switch between the first configuration and the second configuration at frequency of at least 60 Hz. This would allow each eye of a viewer to see a separate image by sending a different image to each eye, therefore allowing a viewer to see a 3D image.

According to a further aspect of the disclosure there is provided an assembly for reversibly reducing a viewing angle, the assembly comprising: a device as described above; and a controller for switching the device between the first configuration and the second configuration.

According to a further aspect of the disclosure, there is provided a method of reversibly reducing a viewing angle using a device comprising: a first quarter waveplate; a second quarter waveplate above the first quarter waveplate; a first polariser above the second quarter waveplate; wherein the first quarter waveplate is configured to receive a polarised light source, wherein a polarisation axis of the first polariser is configured to be substantially perpendicular to a polarisation axis of the polarised light source; wherein the method comprises switching the device between a first configuration and a second configuration; wherein in the first configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one activated zone; and wherein in the second configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one non-activated zone.

According to a further aspect of the present disclosure, there is provided a method of manufacturing a device for reversibly reducing a viewing angle, the method comprising: forming a first quarter waveplate; forming a second quarter waveplate above the first quarter waveplate; forming a first polariser above the second quarter waveplate; wherein the first quarter waveplate is configured to receive a polarised light source, wherein a polarisation axis of the first polariser is configured to be perpendicular to a polarisation axis of the polarised light source; wherein the first quarter waveplate and the second quarter waveplate are configured to be switchable between a first configuration and a second configuration; wherein in the first configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one activated zone; and wherein in the second configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one non-activated zone.

The proposed device provides a highly manufacturable, electronically switchable, privacy screen. The privacy screen may be a dynamic built-in privacy screen for LCDs which can be used in smartwatches, mobile phones, tablets, laptops, TVs, ATMs, airports, and banks. The device may also be used with non-electronic sources of light such as windows or mirrors. The device may also be used to allow each eye of a viewer to see a separate image without the need for any eyewear, therefore allowing a user to see a 3D image. This would be achieved by sending a different image to each eye of a viewer.

This device provides a dual LC-cell based switchable privacy screen which, when enabled, produces a dark/blocked image at high viewing angles. When disabled, a normal wide viewing angle is restored. The device is formed on plastic because the substrate thinness affects the performance of the device. A thinner device is lighter and has improved viewing performance. Furthermore, the use of a thin plastic substrate increases the controllability of the threshold viewing angle of the device. The proposed device stacks cells -this can be achieved because of the use of 40 microns TAC which is very thin. A Dual LC Cell design on thin plastic substrates to allow necessary proximity between the two cells for high performance privacy.

A thick glass substrate, as used in state-of-the-art device, would reduce the performance of the device. Thick glass, as used in conventional devices, would make the whole product heavy and thicker. A thick glass substrate would also absorb some of the light, reducing the viewing performance of the device.

Thicker glass will also reduce the controllability of the threshold image blocking angle that arises from parallax of the two LC planes, as they would be forced to be separated by a large distance when glass is used.

The privacy screen may be integrated within a display, so that the display is a switchable display in which the privacy screen can be turned on and off. Dynamic switching is enabled by having two waveplates, which may be formed using patterned electrodes, which are offset from each other to create a threshold viewing angle, for example, 30°.

The proposed device has the following advantages over state-of-the-art privacy screens: * The ability to electrically switch the privacy screen on and off; * The privacy screen may be assembled with an LCD, or other type of display; * The wide angle privacy mode is dark, not light, like some other approaches; * The device can be built entirely on plastic films; * The device can be simply integrated with an LCD due to the thinner module resulting in lower manufacturing cost; * The device has a reduced weight and cost of the final product.

Brief Description of the Drawings

Some preferred embodiments of the disclosure will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 shows a cross section of a display device with an integrated privacy screen, according to one embodiment of the disclosure; Figure 2 shows a perspective view of two waveplates of the device according to one embodiment of the disclosure, in which the waveplates have a checker board pattern when the device is switched on; Figure 3 shows a schematic illustrating the reduced viewing angle of a device according to an embodiment of the disclosure; Figure 4 shows a perspective view of two waveplates and two polarisers of the device according to one embodiment of the disclosure, in which the waveplates are unpatterned when the device is switched off; Figure 5 shows a cross section of a display device with an integrated privacy screen, according to a further embodiment of the disclosure; Figure 6 shows a cross section of privacy screen according to a further embodiment of the disclosure; Figure 7 shows a cross section of a privacy screen according to a further embodiment of the disclosure, in which the privacy screen includes a second polariser; Figure 8 shows a perspective view of two waveplates of the device according to one embodiment of the disclosure, in which the waveplates have a horizontal striped pattern when the device is switched on; Figure 9(a) shows two waveplates of the device according to one embodiment of the disclosure, in which the waveplates have a repeating triangular pattern when the device is switched on; Figure 9(b) shows two waveplates of the device according to one embodiment of the disclosure, in which the waveplates have a repeating spotted pattern when the device is switched on.

Detailed Description of the Preferred Embodiments

Embodiments will now be described by way of example only.

Figure 1 shows a cross section of a display device with an integrated privacy screen, according to one embodiment of the disclosure. In this embodiment the privacy window is integrated with an LCD.

The privacy screen includes two quarter waveplates or waveplate cells: a first quarter waveplate 105 and a second quarter waveplate 110. The second quarter waveplate is located parallel to and above the first quarter waveplate 105. A polariser 115 is located above and parallel to the waveplates 105, 110. The polariser 115 has a polarisation axis perpendicular to the polarisation axis of the light from the polarised light source, shown in this embodiment as a display 155 with a top polariser 120. In this embodiment, the top polariser 120 of the display 155 would generally have a polarisation axis perpendicular to the polarisation axis of the first polariser 115.

Each of the two quarter waveplate cells 105, 110 includes a liquid crystal (LC) layer, between two alignment layers, which are formed in-between a pair of electrode layers of laterally spaced electrodes. In this embodiment the electrodes are Indium tin oxide (ITO) electrodes patterned on a Cellulose triacetate (TAC) film. The TAC film can be replaced with any non-birefringent material such as Polyimide (PI) or Cyclo Olefin Polymer (COP). But transparent PI is expensive and COP distortion is very high. TAC has the same birefringence as glass but is much thinner, meaning overall better than glass optically (as well as being thinner, lighter, and shatterproof). No thin film transistors (TFTs) are needed in either of the waveplate cells, 105 or 110. The waveplates 105, 110 may also include spacers or pillars (not shown) between the two alignment layers in the waveplate 105, 110.

By electrically activating the quarter waveplates, 105 and 110, and by applying a voltage to the electrodes, the properties of the liquid crystal within the waveplate cells 105, 110 are altered. Depending on whether the electrodes are switched on or off, the liquid crystal between each pair of electrodes can either act as a quarter waveplate or allow light through without altering the polarisation of the light.

The waveplate cells, 105 and 110 are each quarter wave plates that can powered or unpowered by application or removal of a voltage to either act as a patterned quarter wave plate, or an unpatterned quarter wave plate (or pass-through).

When the device is switched on and in privacy mode, a voltage is applied the electrodes, which "pixelates" the quarter waveplates 105, 110 so that light passing through some areas of the waveplate will be subject to a quarter wave phase shift, whereas light passing through other areas will receive no phase shift. The checkerboard pattern of the electrodes may correspond and be aligned to the checkerboard pattern of the waveplate. This allows embodiments of the device which show a viewer a 3D image. Alternatively, the checkerboard pattern of the electrodes may not be aligned to the checkerboard pattern of the waveplate or may be anti-aligned to the checkerboard pattern of the waveplate.

Figure 2 shows a perspective view of two waveplate cells 105, 110 of the device according to one embodiment of the disclosure, in which the waveplates 105, 110 have a checker board pattern when the device is switched on. The electrodes are located such that the LC between the electrodes forms a checker board pattern. The checker board pattern of the LC within the first waveplate 105 is staggered with respect to the checkerboard board pattern of the LC within the second waveplate 110. The checkerboard pattern waveplate has waveplate regions 125, 135 that act as waveplates, and regions 130, 140 that act as pass-throughs.

Light passing through either of the quarter waveplate regions 125, 135 orthogonally will pick up one quarter wave phase shift only, (either from the first waveplate region 125 or from the second waveplate region 135, but not from both waveplates). Therefore light normally incident through the device, E, passes through one of the quarter waveplate regions 125, 135 and reaches a viewer, D, viewing the device at a narrow viewing angle. This is because the quarter waveplate regions rotate the polarisation of the light by 90° so that light from the polarised light source can then pass through the device polariser.

Light passing through at a higher angle will pick up either two quarter wave phase shifts, or zero phase shift. Light travelling at a wide angle through the device, E', passes through two quarter waveplates regions 125, 135 or zero quarter waveplate regions 130, 140 and is blocked from reaching a viewer, D', at a wide angle to the display. This is because the two quarter waveplates regions 125, 135 rotate the polarisation of the light by 180°, and light passing through zero waveplate regions 130, 140 is not rotated at all, so that light from the polarised light source cannot pass through the device polariser 115. In both cases (when the light passes through zero quarter waveplate regions or two quarter waveplate regions 125, 135) this light cannot exit from the polarizer 115, so the image is blocked at higher viewing angles.

As the waveplates 105, 110 have a checkerboard pattern, this restricts the angle of vision both horizontally and vertically. This blocks users from viewing the device at a high viewing angle, in two dimensions. The checkerboard waveplates 105, 110 behave similar to vertical and horizontal blinds on the same blind module.

The first polarizer 115 is at a 90 degree rotation to the polarizer of the display 120, so that, if the two waveplates, 105 and 110, were not included, no light would pass through the first polarizer 115 on the front of the device. This is similar to the situation where light passing through zero waveplate regions is blocked.

The two waveplate cells 105, 110 are separated by a gap, C. In this embodiment the gap, C, is made from an adhesive, A, as the waveplate cells 105, 110 are fabricated separately. Alternatively the gap may be formed of a photoresist (such as SUB, UVHC7000, S1800) if 110 is processed directly on top of 105. The thickness of the gap, C, is the adhesive thickness, A, and two times the TAC films thickness, T. The adhesive, A, in this embodiment is a dielectric adhesive.

The electrodes have a width S1 and the distance between laterally adjacent electrodes is given by 52. The ratio between the gap, C, between waveplate cells and the spacing between the ITO electrodes, S, is usually kept at C:S = 2:1. In this embodiment, Si and S2 are similar values, therefore enabling no light transmission at an angle of more than 30° to a normal through the device.

One of the quarter waveplates, in this embodiment 105, in its unpowered state acts as a blanket quarter wave plate, and the other quarter waveplate 110 acts as a blanket pass-through. Therefore both of the waveplate cells 105, 110 in unpowered state are unpatterned, however one rotates the polarisation of all light passing through and one has no effect on light passing through. Alternatively, there are various options here that achieve the same or similar effect. These are achieved by rubbing directions of the alignment layer, and electrode locations in relation to the other cell.

With the waveplates 105, 110 in place, and unpowered, light will leave the polarised light source, in this embodiment the display 155, and pass through the waveplates 105, 110 and then through the display polarizer 120, regardless of viewing angle. This mode is referred to as normal mode, as when unpowered the display will act as a normal display.

This approach using two waveplates 105, 110 and a polariser 115, can be used on the front of any display provided the light leaving the display is polarized, which is the case for LCD displays and also most OLEDs, which contain a circular polarising film (POL).

In this embodiment, the first polariser 115, the two waveplate cells 105, 110 are integrated in a passive matrix 150. The device is formed on an active matrix 155, including a top polariser 120, an LCD cell 160, a bottom polariser 165, and a backlight module 170. The active matrix 155 and the passive matrix 150 may be manufactured separately, and integrated at a later time.

In both normal and privacy mode, ideally the image in the normal direction is unaffected and only wider viewing angles should be affected. Nevertheless, the presence of the additional POL may slightly reduce the brightness of the display. This effect can be reduced by using a partial (leaky) polarizer -thereby increasing brightness in the normal viewing direction at the expense of the effectiveness of the privacy function at wider viewing angles. The reduction of the brightness at wide viewing angles does not have to be perfect for the device to be usable, since any reduction that makes the display harder to read can stop viewers viewing the display from wide angles.

The adhesive may be formed in the gap by i) 2x single demounts (then remove the inside Glass on both cells), ii), followed by a double demount process. The two cells (W1 and W2) are processed separately and then laminated with W1 on top of W2 with an adhesive in-between. W1 is processed separately to W2 as in Figure 7. Then both cells are laminated together with an adhesive in between as shown in Figure 7. The two structures are built separately and then laminated together.

The bottom row of the ITO electrodes does not need to be aligned to the display. The electrodes can be laminated and attached to a display at any angle. The ITO electrodes are not related to the pixel size.

This embodiment is built on a plastic substrate. This is because the substrate thinness is a key part of the optical design -a thick glass substrate, as used in conventional displays, would produce sub-optimal performance.

Figure 3 shows a schematic illustration of the reduced viewing angle of a device according to an embodiment of the disclosure, when the device is in privacy mode. The line 300 represents a normal to the plane of the device. For example, the plane 305 shown could be the top surface of the device. A first user, D, can view light, E, from the device that is parallel to the normal 300.

A second user, D', is viewing the device from an angle O. If the angle e, is above a threshold value, the user will not be able to view light, E', from the device from a wide viewing angle. The threshold value in the embodiment shown in Figure 1 was 30°, however the threshold angle value can be greater or smaller. The threshold angle value can be altered by changing the width and geometry of the waveplate patterns and the distance between waveplates.

Figure 4 shows a perspective view of two waveplate cells 105, 110 and two polarisers 115, 120 of the device according to one embodiment of the disclosure, in which the waveplates 105, 110 are unpatterned when the device is switched off (in normal mode). The lower polariser 120 may be included in the device or may represent a polarised source of light.

The first waveplate cell 105, in the normal mode, is acting a blanket quarter waveplate. This means that light passing through any section of the first waveplate 105 has its polarisation axis rotated by 90°. The second waveplate cell 110, in the normal mode, is acting as a blanket pass-through plate. This means that light passing through any section of the second waveplate 110 has its polarisation axis unchanged by the second waveplate 110.

As the two polarisers 115, 120 have polarisation axes that are perpendicular to each other, without the waveplates 105, 110 no light would get through the front polariser from the back polariser 120. However as the light from the back polariser 120 is rotated by 90° by the first waveplate 105, the light can then pass through the front polariser 115.

Figure 5 shows a cross section of a display device with an integrated privacy screen, according to a further embodiment of the disclosure. In this embodiment the device is integrated with a display device. One layer of electrodes of the first waveplate cell 105 are patterned onto the polariser of the display 120. The two waveplate cells 105, 110 are still separated by a gap, however this gap is filled with dielectric, G. One layer of electrodes of the second waveplate 110 are patterned onto the dielectric, G. In this embodiment the privacy screen can be built directly on top of the display. This reduces process steps and results in a thinner device.

It also understood that simpler architectures than that shown above could also be realised, for example by using the upper TAO film of one waveplate as the substrate for the other waveplate (meaning only 3 TAC sheets in the whole structure). This is similar to the embodiment shown in Figure 5. In this embodiment there would be no adhesive because the central TAC can be a dual substrate with electrodes on both sides. This can be laminated onto one polariser with another polariser on top. The TAC film may also be replaced with polariser, and one polariser can replace the TAC film in each waveplate structure.

The two waveplates 105, 110 may be directly built onto the display, or integrated using a roll to roll lamination. The privacy screen can be fabricated separately to the top polariser. The whole module can then be laminated directly on top of the LCD display.

For the method of processing both waveplate cells, 105 and 110, monolithically as in the embodiment of Figure 5, waveplate cell 110 is processed first directly on the polariser 120 of the display. The top glass of 110 is demounted from module. A spacer (such as SU8 or UVHC7000) is deposited followed by ITO electrodes and patterning of ITO electrodes. The top plate of waveplate cell 105 is then processed with ODF (One Drop Fill). This is a method used to assemble the top and bottom plate together with Liquid Crystal (LC) in-between. Fill is added, the substrate is aligned, and an edge seal is added. The whole process is done under vacuum. These steps may apply to all embodiments. The top glass of waveplate cell 105 is demounted and additional polariser laminated on top.

Figure 6 shows a cross section of privacy screen according to a further embodiment of the disclosure. In this embodiment, the privacy screen is not provided with a source of polarised light, but can be attached to a separate source of polarised light. This may be used on, for example, existing LCDs or OLED displays, and other information displays.

Figure 7 shows a cross section of a privacy screen according to a further embodiment of the disclosure, in which the privacy screen includes a second polariser 120. In this embodiment, the privacy screen can be attached to any source of light. This would work, for example, on windows or mirrors.

Figure 8 shows a perspective view of two waveplate cells 105, 110 of the device according to one embodiment of the disclosure, in which the waveplates 105, 110 have a horizontal striped pattern when the device is switched on. In the privacy mode each of the two waveplates 105, 110 have waveplate regions 125, 135 that are acting as quarter waveplates, and regions 130, 140 that are acting as pass-throughs. The quarter waveplate regions 125 of the first waveplate 105 are aligned with the pass-through regions 140 of the second waveplate 110. The pass-through regions 130 of the first waveplate 105 are aligned with the quarter waveplate regions 135 of the second waveplate 110. This blocks viewers from viewing the device at a wide viewing angle, but only in a single dimension (vertically in the embodiment shown). Whilst Figure 8 shows horizontal stripes, the pattern could alternatively been vertical stripes which would block viewing from a wide horizontal viewing angle.

Figure 9(a) shows two waveplate cells 105, 110 of the device according to one embodiment of the disclosure, in which the waveplates have a repeating triangular pattern when the device is switched on. Figure 9(b) shows two waveplates 105, 110 of the device according to one embodiment of the disclosure, in which the waveplates have a repeating spotted pattern when the device is switched on. These are alternative waveplate patterns that could be used, although their effectiveness may vary in comparison to the checkerboard pattern waveplates.

There are also other uses of this structure, or slight variants of it, for example it could be used to rapidly switch a narrow viewing angle between two different angles. This could be used to send different images to each of your eyes, e.g. for 3D images.

The skilled person will understand that in the preceding description and appended claims, positional terms such as 'top', 'above', 'overlap', 'under', 'lateral', etc. are made with reference to conceptual illustrations of a device, such as those showing standard cross-sectional perspectives and those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to a device when in an orientation as shown in the accompanying drawings.

Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the disclosure, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS: 1. A device for reversibly reducing a viewing angle, the device comprising: a first quarter waveplate; a second quarter waveplate above the first quarter waveplate; a first polariser above the second quarter waveplate; wherein the first quarter waveplate is configured to receive a polarised light source, wherein a polarisation axis of the first polariser is configured to be substantially perpendicular to a polarisation axis of the polarised light source; wherein the first quarter waveplate and the second quarter waveplate are configured to be switchable between a first configuration and a second configuration; wherein in the first configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one activated zone; and wherein in the second configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one non-activated zone.
2. A device according to claim 1, wherein in the first configuration the at least one activated zone comprises a patterned waveplate zone, and wherein in the second configuration the at least one non-activated zone comprises an unpatterned waveplate zone.
3. A device according to any of claim 1 or 2, wherein in the first configuration each activated zone comprises a striped patterned waveplate zone, and wherein the striped patterned waveplate zone comprises an alternating pattern of stripes.
4. A device according to any of claims 1 or 2, wherein in the first configuration each activated zone comprises a checkerboard patterned waveplate zone, and wherein the checkerboard patterned waveplate zone comprises an alternating pattern of squares.
5. A device according to claim 4, wherein the checkerboard patterned waveplate zone may comprise a pattern of crossed horizontal lines and vertical lines to form alternating squares.
6. A device according to any of claims 2 to 5, wherein in the first configuration each patterned waveplate zone comprises: a first plurality of regions configured to alter the polarisation of light passing through the first plurality of regions of the patterned waveplate zone; and a second plurality of regions configured to allow light to pass through the second plurality of regions of the patterned waveplate zone without altering the polarisation of the light.
7. A device according to claim 6, wherein in the first configuration the first plurality of regions of the first waveplate are aligned with the second plurality of regions of the second waveplate.
8. A device according to claim 6 or 7, wherein the second waveplate is positioned such that normally incident (polarized) light passing through the first plurality of regions of the first waveplate will pass through one of the second plurality of regions of the second waveplate, and normally incident (polarized) light passing through the second plurality of regions of the first waveplate will pass through one of the first plurality of regions of the second waveplate.
9. A device according to any preceding claim, wherein in the second configuration, one of the first waveplate or the second waveplate is configured to alter the polarisation of light passing through the at least one non-activated zone of the one of the first waveplate or the second waveplate, and the other of the first waveplate or the second waveplate is configured to allow light to pass through the at least one non-activated zone of the other of the first waveplate or the second waveplate without altering the polarisation of the light.
10. A device according to any preceding claim, wherein in the first configuration the device is configured to block light from the polarised light source from an angle greater than 30° to a normal through the device from passing through the device.
11. A device according to any preceding claim, wherein in the second configuration the device is configured to allow light from the polarised light source from an angle greater than 30° to a normal through the device from passing through the device.
12. A device according to any preceding claim, wherein the first waveplate and the second waveplate are separated by a predetermined distance, C.
13. A device according to claim 12, wherein in the first configuration each of the first plurality of regions has a predetermined width of value S1, and wherein in the first configuration each of the second plurality of regions has a predetermined width of value S2.
14. A device according to claim 13, wherein S1 and S2 are substantially equal.
15. A device according to claim 13 or 14, wherein the ratio of C:S1 is approximately 2:1.
16. A device according to any preceding claim, wherein the device further comprises a polarised light source.
17. A device according to claim 16, wherein the polarised light source comprises a display.
18. A device according to any preceding claim, wherein the device further comprises a second polariser, and wherein the first quarter waveplate is above the second polariser, and wherein a polarisation axis of the second polariser is perpendicular to a polarisation axis of the first polariser.
19. A device according to any preceding claim, wherein each of the first quarter waveplate and the second quarter waveplate comprise: two electrode layers; two alignment layers between the electrode layers; and a liquid crystal layer between the alignment layers.
20. A device according to claim 19, wherein the electrode layers are configured such that when the electrode layers are in a powered state the device is in the first configuration, and when the electrode layers are in an unpowered state the device is in the second configuration.
21. A device according to claim 19 or 20, wherein for each of the first quarter waveplate and the second quarter waveplate, at least one of the two electrode layers is formed on a plastic substrate.
22. A device according to any of claim 19, 20, or 21, wherein the electrode layers comprise a plurality of laterally spaced electrodes.
23. An eyewear apparatus comprising a device according to any preceding claim, wherein the eyewear apparatus is configured to switch between the first configuration and the second configuration at a predetermined frequency.
24. An assembly for reversibly reducing a viewing angle, the assembly comprising: a device according to any preceding claim; and a controller for switching the device between the first configuration and the second configuration.
25. A method of manufacturing a device for reversibly reducing a viewing angle, the method comprising: forming a first quarter waveplate; forming a second quarter waveplate above the first quarter waveplate; forming a first polariser above the second quarter waveplate; wherein the first quarter waveplate is configured to receive a polarised light source, wherein a polarisation axis of the first polariser is configured to be perpendicular to a polarisation axis of the polarised light source; wherein the first quarter waveplate and the second quarter waveplate are configured to be switchable between a first configuration and a second configuration; wherein in the first configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one activated zone; and wherein in the second configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one non-activated zone.
26. A method of reversibly reducing a viewing angle using a device comprising: a first quarter waveplate; a second quarter waveplate above the first quarter waveplate; a first polariser above the second quarter waveplate; wherein the first quarter waveplate is configured to receive a polarised light source, wherein a polarisation axis of the first polariser is configured to be substantially perpendicular to a polarisation axis of the polarised light source; wherein the method comprises switching the device between a first configuration and a second configuration; wherein in the first configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one activated zone; and wherein in the second configuration each of the first quarter waveplate and the second quarter waveplate comprises at least one non-activated zone.