JP3521666B2 - Polarization separation element and projection display device using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization separation element mainly used for illuminating a spatial light modulation element utilizing polarization of light, and a projection display device using the polarization separation element.

[0002]

2. Description of the Related Art Conventionally, a CRT is used as a projection display device for enlarging and projecting an original image using a projection lens,
A device using a light source and a spatial light modulator is known.
As a spatial light modulator, a transmissive liquid crystal panel using twisted nematic liquid crystal is known. It is easy to downsize the projector, and if a panel with a large number of pixels is used, a high-definition image can be projected. It has been widely put to practical use because it is possible and the mass production technology for liquid crystal panels has been established for direct-view applications.

Since the twisted nematic liquid crystal utilizes the polarization of light, such a spatial light modulator has a polarizer on the incident side and an exit side. Of the light that illuminates the spatial light modulator, the polarization state of the linearly polarized light that passed through the incident side polarizer is spatially changed, and the amount of light that passes through the exit side polarizer is controlled to form an optical image. To do.

A projection display device using a spatial light modulator generally illuminates the spatial light modulator using a lamp that emits natural light. When the spatial light modulator uses polarization of light, the polarizer on the incident side passes only about half the natural light emitted by the lamp, and other light is reflected or absorbed and becomes a loss. .

On the other hand, various techniques called polarization conversion have been proposed. This is to separate the natural light of the light source into the light of the necessary polarization component and the light of the polarization component orthogonal to this, and rotate the polarization plane of the light of the polarization component that cannot be used as it is by 90 degrees to obtain two lights. After aligning the planes of polarization of the above, the light is supplied to the spatial light modulator to utilize them.

Therefore, in a projection display device using polarization conversion, a polarization splitting element for splitting natural light into two polarized light components whose polarization directions are orthogonal to each other and a polarization plane of one of the split polarized light beams are 90 degrees. A polarization plane rotating element that rotates by a degree is required. As a polarization separation element, a polarization separation multilayer film utilizing Brewster's angle and interference is widely known, and there are a flat plate type and a prism type polarization separation element.

On the other hand, as a polarization plane rotation element, a phase film called a λ / 2 plate is generally known. This is an optically transparent organic film stretched in a uniaxial direction to give optical anisotropy, and its thickness and optical anisotropy are controlled to correspond to 1/2 of the wavelength λ for transmitted light. It provides a phase difference.

When linearly polarized light having a plane of polarization in the direction of 45 degrees with respect to the optical axis is incident on the λ / 2 plate, the emitted light is linearly polarized light with the plane of polarization rotated by 90 degrees.

[0009]

None of the conventionally proposed polarization conversion configurations or optical systems used therefor achieve sufficient effects from their original purpose.

Hereinafter, in the optical path from the light source to the spatial light modulator, the light in the polarization direction originally used by the spatial light modulator is referred to as primary polarization, and the light in the polarization direction orthogonal to the polarization plane is rotated before the plane of polarization is rotated. Is called secondary polarized light. The optical path through which the primary polarized light passes is defined as the primary optical axis, and 2
The optical path through which the secondary polarized light passes is the secondary optical axis.

To realize polarization conversion, the light utilization efficiency of the entire optical system must be sufficiently high for both primary polarized light and secondary polarized light. If the efficiency of primary polarization is significantly reduced by using polarization conversion as compared with the case where it is not used, the increase in light utilization efficiency due to the introduction of polarization conversion will be reduced, and the original purpose of improving brightness will be reduced. Can't achieve enough.

Further, the secondary polarized light should not increase uneven brightness or uneven color of the light illuminating the spatial light modulator. The illumination unevenness of the illumination light causes unevenness in brightness and color of the projected image, which is a problem.

Further, the means for realizing the polarization conversion is one that makes the optical paths of the primary polarized light and the secondary polarized light extremely long, one that greatly increases the size of the optical system, and one that makes the cost of the optical system extremely expensive. , Must not be. There are problems that the light loss in the long optical path increases, the projection display device becomes large, and the cost becomes high.

For the above reasons, as conventional polarization conversion techniques, Japanese Patent Laid-Open No. 3-13983 and Japanese Patent Laid-open No. 4-6331 are known.
No. 8, JP-A-4-177335, JP-A-5-
The materials described in Japanese Patent No. 27203 and Japanese Patent Application Laid-Open No. 7-64075 are not sufficient. In both cases, since the prism in which the polarization separation multilayer film is vapor-deposited is used, the polarization separation element is expensive and large, and the optical path length from the light source to the spatial light modulation element is increased, which increases the optical path length of the primary polarization and the secondary polarization. However, there is a problem that there is a large difference between the primary polarized light and the secondary polarized light, and the effect of brightening the projected image is not sufficient.

In particular, it is important that the optical path length from the light source to the spatial light modulator is the same for the primary polarized light and the secondary polarized light. With respect to both the primary polarized light and the secondary polarized light, the conditions under which the light emitted from the light source is collected, transmitted, and illuminated can be made the same. This is to increase the light utilization efficiency for light in both polarization directions and to make the illumination light uniform.
Is preferred, which is preferable. It is possible to provide a bright projected image with little display unevenness.

On the other hand, the polarization splitting element disclosed in Japanese Patent Laid-Open No. 174502/1993 is one in which a uniaxial birefringent material having an aligned optical axis is sandwiched between the interfaces of two prisms, and the two polarization directions are different. The polarized light is separated by selectively totally reflecting only one of them. This is excellent in heat resistance and polarization separation efficiency, but it is expensive because the polarization separation element is large and a glass prism on a bulk is used. In addition, there is a problem because the optical path length that acts becomes long.

The optical system disclosed in Japanese Patent Laid-Open No. 4-234016 has the same optical path length from the light source to the spatial light modulator for the primary polarized light and the secondary polarized light. This is preferable for handling light of both polarizations under the same conditions, but the configuration disclosed in this publication has a problem that the entire optical path length is long and the size of the entire set becomes large. Also, the number of parts is large.

Further, the optical system disclosed in Japanese Unexamined Patent Publication No. 6-202094 discloses an example of an optical system which can utilize both primary polarized light and secondary polarized light by using a thin polarization separation element. . The structure of this optical system is shown in FIG.

The natural light emitted from the lamp 901 is condensed by the parabolic mirror 902 and the first lens array 90.
4, the second lens array 905, and then the liquid crystal panel 90.
Illuminate 7. The first lens array 904 splits the illumination light flux, and the split light flux is expanded to an appropriate size by the second lens array 905. The convex lens 908 superimposes each divided light flux on the panel. The convex lens 909 near the panel makes the principal ray at each field angle of the illumination light parallel to the optical axis.

Reference numeral 903 denotes a polarization beam splitting element, and an example of its structure is shown in FIG. This causes the light of primary polarization and the light of secondary polarization to be emitted as light whose traveling directions differ by an angle θ. As a result, the spots of the light flux that the first lens array 904 converges on the apertures of the second lens array 905 are deviated by a predetermined distance in the direction of the angle θ between the primary polarized light and the secondary polarized light. In the vicinity of the aperture of the second lens array 905, the phase difference plate 906 is selectively acted only on the converged spot of the secondary polarized light to rotate this plane of polarization by 90 degrees, and the light is emitted from the second lens array 905. The polarization planes of the secondary polarized light and the secondary polarized light are aligned in the same direction. By making this correspond to the polarization direction of the incident side polarization plate of the liquid crystal panel 907, an optical system with high light utilization efficiency can be realized.

An example of the configuration of the polarization beam splitting element 903 will be supplemented. 911 is a sawtooth prism array substrate, 912 is a flat substrate, and 913 is a birefringent optical material layer, and a liquid crystal layer, an organic film, a monomer, etc. can be used. Combining a prism layer made of a birefringent material adjacent to a prism whose refractive index is isotropic, and making the conditions of refraction at the prism interface different for orthogonal polarization directions,
It is widely known as a Wollaston prism that separates two polarized lights and makes the traveling directions different. The polarization beam splitting element 903 is an array of the polarization beam splitting element 903, and the point of using expensive calcite as a birefringent material is used by orienting an organic material such as a liquid crystal or a monomer in a uniaxial direction. .

The polarization separation element 903 can obtain the above operation in principle, but actually has the following problems. Since liquid crystals and organic films are relatively weak to heat, there is a problem in arranging them near a light source that emits high heat and using them.

Further, it is considered that the periodic pitch of the sawtooth prism array is required to be at least 1 mm or more in consideration of processing a good shape. In this case, the thickness of the birefringent material layer also needs to be at least about 1 mm. A molecule with birefringence such as liquid crystal is
It is widely known that uniaxial orientation is performed by a method such as rubbing, but generally, it is possible to orient to a thickness of several tens of microns at the maximum, and evenly orient a thick layer of several millimeters uniformly. The method and material for making it are not widely known. Regarding this point, JP-A-6-20
It is not disclosed in Japanese Patent Publication No. 2094.

Therefore, the polarization separation element having the above-described structure and the projection display apparatus using the same have a serious problem in realizing the polarization separation element having a desired function.

Further, Japanese Patent Laid-Open No. 8-234205 discloses
In view of the above points, a configuration in which a polarization prism having a bulk shape and a polarization selective mirror made of a multilayer film are combined is disclosed as a polarization separation element. An example of a method of arranging small polarization selective prisms in an array to form a thin polarization separation element is also disclosed.

However, both of these methods have the problems that a long optical path length is required for arranging the prisms, the prisms are expensive, and the structure of the prism array is complicated so that sufficient efficiency cannot be obtained. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a thin and highly efficient polarization separation element that is relatively easy to implement. Further, it is another object of the present invention to provide a projection display device that uses the polarization separation element and provides a bright display image with high light utilization efficiency.

[0028]

[0029]

[0030]

In order to solve the above-mentioned problems, the first polarization separation element of the present invention uses incident natural light as an A polarization component having an oscillation component of an electric field in the azimuth A and A polarization separation element that separates and outputs a B polarization component having a vibration component of an electric field in an azimuth B orthogonal to A. The polarization separation element is configured by arranging a plurality of units of polarization separation elements two-dimensionally. , One unit of the polarization separation element is
The light of the A-polarized component and the light of the B-polarized component form a predetermined separation angle in a predetermined direction and are emitted so that their traveling directions are different from each other, and combined with the polarization separation element.
To the perfect circular first lens array and second lens array
On the other hand, the second lens array should improve the pupil utilization rate.
With a unique aperture shape and array, and on the second lens array
By the real image formed by A polarized light and the B polarized light
Two-dimensionally arranged according to the distance from the real image
A plurality of the polarization separating elements may be arranged in the polarization direction depending on the arrangement position.
The feature is that the light separation angles are different .

Preferably, in the first polarization splitting element of the present invention, the polarization splitting element has a periodic structure in the uniaxial direction C along the surface of the transparent substrate arranged substantially orthogonal to the optical axis of the incident light. The diffraction grating has an optical anisotropic layer formed adjacent to the diffraction grating, and the optical anisotropic layer is orthogonal to the refractive index (N2) in the direction C on the surface of the substrate. The refractive index (N1) in the direction D has a different refractive index from each other , and the refractive index (N0) of the diffraction grating is the refractive index in the direction D.
By selecting the bending ratio (N1) to be almost equal,
Only one polarization component of the A polarization component or the B polarization component with respect to the optical axis is selectively acted to diffract the light of the polarization component by a predetermined angle, and the pitch of the periodic structure of the diffraction grating is changed. A second lens which is different and combines the separation angle of the polarization separation element with the polarization separation element.
The openings are made different according to the shape and arrangement of the openings .

Further, in order to solve the above problems, the first projection type display device of the present invention comprises a light source which emits natural light,
A condensing unit that condenses the light emitted from the light source to form light that travels in a substantially uniaxial direction, a polarization separating element on which the light emitted from the condensing unit is incident, and a polarization separating unit disposed near the polarization separating unit. One lens array, a second lens array on which light emitted from the first lens array is incident, and a polarization plane which is arranged in the vicinity of the second lens array and selectively acts on a part of the light passing through the lens array. Rotating means, second
It is equipped with a spatial light modulator that is irradiated with light emitted from the lens array and a projection lens that projects an optical image on the spatial light modulator. The spatial light modulator acts on linearly polarized light to form an optical image. The first lens array has a plurality of first lenses arranged two-dimensionally, and the second lens array has a plurality of second lenses paired with the first lens two-dimensionally arranged. The separation element is the above-mentioned first polarization separation element of the present invention, and the polarization separation element changes the polarization separation angle according to the position of the corresponding first lens, and has different traveling directions A.
The light of the polarization component and the light of the B polarization component are converged by the first lens adjacent to different positions of the corresponding aperture of the second lens, and the polarization plane rotating means has one polarization on the aperture of the second lens. The polarization plane of the light of the polarization component is rotated approximately 90 degrees by selectively acting only on the polarization light of the component, and the polarization plane of the light of the A polarization component and the polarization of the light of the B polarization component irradiated on the spatial light modulator are polarized. The wavefronts are made to coincide with each other so that they can be used.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is characterized in that a polarization separation element is formed by combining a diffraction grating and a uniaxial optically anisotropic layer. Prior to a detailed description of the present invention, first,
General publicly known matters regarding the diffraction grating will be described.

FIG. 1 shows an example of a diffraction grating 11 formed by periodically forming sawtooth-shaped minute structures. The periodic pitch of the sawtooth shape is D, and the maximum height (depth) is H.

Here, if the maximum height H [m] has a phase difference of 2π with respect to the light 12 of wavelength λ [m] that is incident from the normal direction of the substrate, almost all of the incident light 12 is obtained. Is bent by an angle θ as the + 1st order diffracted light, and the outgoing light 1
2 '.

In this case, the maximum height H [m] is (Equation 1), and the diffraction angle θ is (Equation 2). However, Ns is the refractive index of the diffraction grating substrate, and Na is the refractive index of the medium enclosing the diffraction grating.

[0037]

[Equation 1]

[0038]

[Equation 2]

FIG. 2 is a structural example of the diffraction grating 15 known as a binary optical element. This is an approximation of the sawtooth-shaped microstructure of FIG. 1 with a stepped step structure. In this case, the number of floors of the flat part of the stairs is called the number of levels, and the diffraction grating 15 has 7 levels.

The binary optical element has an advantage that a fine shape can be formed relatively easily by photolithography using a semiconductor exposure apparatus (stepper optical system). Also in this case, if the phase difference given by the height H is 2π, most of the incident light 16 is emitted as the + 1st order diffracted light 16 ′. Regarding the height H and the pitch D, (Equation 1), (Equation 2)
Similarly holds.

Further, for example, the number of levels is 2, 4, 8, 16
And the theoretical diffraction efficiency is 40.5.
%, 81%, 95%, 99%, and if the number of levels is 4 or more, practically sufficient diffraction efficiency can be obtained.

Next, an example of the polarization beam splitting element of the present invention is shown in FIG. 3 and its operation will be described. Polarization separation element 101
Is composed of a diffraction grating substrate 102 and a birefringent layer 103. In order to facilitate the explanation, an orthogonal coordinate system is introduced, the direction along the paper surface is taken as the xy plane, the direction orthogonal to the paper surface is taken as the z axis, and the polarization separation element 101 is two-dimensionally formed on the yz plane. A ray 104 that is divergent and considered as a reference is assumed to be incident along the x-axis.

For example, the diffraction grating 102 is the same as that shown in FIG. 1 and has a sawtooth-shaped microstructure periodically formed at a pitch D in the y-axis direction. The maximum physical height of the sawtooth structure is H. The diffraction grating 102 is formed using an isotropic transparent substrate having a refractive index of N0.

On the other hand, the birefringent layer 103 is formed by orienting a positive uniaxial optical anisotropic body so that its optical axis coincides with the z-axis direction. For the birefringent layer 103, the refractive index in the z-axis direction is N1, the refractive index in the y-axis direction is N2,
N1> N2.

With respect to the naturally polarized light 104 incident from the direction normal to the substrate of the diffraction grating 102 (x axis), the light of the polarization component in which the electric field oscillates in the z axis direction is defined as the primary polarized light 104A. Similarly, the light of the polarization component in which the electric field oscillates in the y-axis direction is the secondary polarization 104B.

For example, the refractive index N of the base material of the diffraction grating 102
0 and the refractive index N1 of the birefringent layer 103 are selected so as to satisfy N0≈N1. In this way, the diffraction grating 102 does not exist for the light of the primary polarization 104A, and the primary polarization 104A of the incident light 104 goes straight through the polarization separation element 101 and is emitted.

On the other hand, since N0> N2, the diffraction grating 102 acts on the light of the secondary polarization 104B, and the secondary polarization 104B is diffracted and emitted.

In this case, the height H of the diffraction grating 102 is
Select so as to satisfy (Equation 3).

[0049]

[Equation 3]

This is a conditional expression from (Equation 1) so that the maximum phase difference given by the diffraction grating for the light of the reference wavelength λ becomes 2π. In such a saw-toothed diffraction grating, the + 1st order diffracted light is theoretically 100% of the light of wavelength λ. However, the reference wavelength λ may be, for example, 550 nm as a wavelength representative of the visible wavelength band. The diffraction angle θ is
(2) using the periodic pitch D of the diffraction grating.

For the above reason, 2 of the incident lights 104
Most of the next polarized light 104B is diffracted by + θ and emitted. That is, the polarized light separating element 101 receives the incident light 104
To separate and emit the primary polarized light 104A and the secondary polarized light 104B whose traveling directions form an angle θ with each other.

Further, the polarization beam splitting element of the present invention may be the polarization beam splitting element 111 shown in FIG. This uses the binary optical element shown in (FIG. 2) instead of the diffraction grating 101 of (FIG. 3). An orthogonal coordinate system similar to that of (FIG. 3) is introduced.

For example, the diffraction grating 112 is a step-like microstructure formed periodically at a pitch D in the y-axis direction.
The number of levels is 7. Specifically, one cycle D is equally divided into seven strip regions and equal step heights H / 6 are sequentially stacked to form a staircase shape. The symbol H is the maximum physical height of the staircase shape. The base material of the diffraction grating 112 is an isotropic transparent material having a refractive index N0, and the birefringent layer 113 is the same as that shown in FIG.

The light of the primary polarized light 114A in which the vibration direction of the electric field is the z-axis direction is not affected by the action of the diffraction grating 112 and goes straight through the polarization separation element 111 and is emitted. On the other hand, the secondary polarized light 114B in which the vibration direction of the electric field is the y-axis direction
Light is diffracted by the diffraction grating 112 and emitted.

Also in this case, the maximum height H of the diffraction grating 112 is
Is selected so that the phase difference given to the reference wavelength λ is 2π. In the step-like binary optical element selected in this way, the + 1st order diffracted light is dominant, and if the number of levels is about 7, the diffraction efficiency is practically sufficient. Secondary polarization 11
The diffraction angle θ of 4B is the same as (Equation 2) using the periodic pitch D of the diffraction grating.

Since the polarization separation elements shown in FIGS. 3 and 4 use a diffraction grating, the birefringent layers 103 and 113 are used.
Is characterized by being very thin. In order to obtain a diffraction angle of about 10 degrees, the pitch D is about several microns, and the height of the diffraction grating is about the same. Therefore, it is extremely easy to fill liquid crystal molecules, liquid crystal monomers, liquid crystal polymers, uniaxial organic materials, etc. in the minute structure part of the diffraction grating and orient them in a predetermined uniaxial direction. An excellent polarization separation element can be obtained.

In particular, in the case of forming a diffraction element with a fine pitch, the binary optical element is excellent in workability. By using the stepper exposure used in the semiconductor exposure apparatus, the processes of resist coating, pattern exposure, and etching are combined to form a diffraction grating with high processing accuracy, excellent mass productivity, low cost, and relatively large area. Therefore, the polarization separation element shown in (FIG. 2) is extremely easy to realize a diffraction grating, and can be realized as an element having higher mass productivity and lower cost.

Specific embodiments of the polarization splitting element and the projection display device of the present invention will be described below with reference to the drawings and numerical examples.

Example 1 of Polarization Separation Element As a first example of the polarization separation element, the one shown in FIG. 3 will be described in more detail.

For example, the diffraction grating 102 has a refractive index of 1.6.
Is an isotropic transparent body. The birefringent layer 103 is formed by orienting a material having positive birefringence with its optical axis aligned with the z axis, and has a refractive index in the z axis direction of 1.6, which is the same as the refractive index of the diffraction grating. To do. The refractive index in the y-axis direction orthogonal to this is 1.45.

The above-described structure can be realized, for example, by curing appropriately generated organic molecules such as liquid crystal polymer and liquid crystal monomer in a state in which they are forcibly aligned on the diffraction grating 101. Examples of the orientation means include applying a rubbing treatment after applying a polyimide film, applying an appropriate magnetic field, and applying an appropriate electric field.

For example, the primary polarized light 104A and the secondary polarized light 10
In order to set the separation angle θ of 4B to 8 degrees, the pitch D of the diffraction grating 102 is set to 3.95 μm using the equation (1).
However, 550 nm, which has the highest visibility, was selected as the reference wavelength λ.

In this case, the diffraction angle θ changes depending on the wavelength, but its degree is small, and there is no particular problem in using it as a polarization separation element. For example, when D = 3.95 μm,
The diffraction angle for blue light with a wavelength of 490 nm is 7.1 degrees, and the diffraction angle for light with a wavelength of 610 nm is 8.8 degrees.

Further, in order to maximize the + 1st-order diffraction efficiency of the secondary polarization 104B, the maximum height H of the diffraction grating is set to H = 3.67 μm from the equation (2). As a result, with respect to the light having the reference wavelength of 550 nm, almost all the light of the secondary polarization 104B is diffracted and separated in the direction of the angle θ. When the wavelength is different, the diffraction efficiency is lowered, but practically sufficient diffraction efficiency can be obtained in the entire visible wavelength band.

(Second Embodiment of Polarization Separation Element) As a second embodiment of the polarization separation element, the one shown in FIG. 4 will be described in more detail. In the first embodiment (FIG. 3)
The configuration and numerical parameters applied to () can be applied to (FIG. 4) in almost the same manner. This makes it possible to construct a polarization beam splitting element having a polarization beam splitting angle of 8 degrees, as in the first embodiment.

By setting the number of levels of the diffraction grating 112 to at least 4 or more, preferably about 8, it is possible to obtain practically sufficient diffraction efficiency.

In the first and second embodiments, the birefringent layer 1
Although 03 and 113 are defined as positive optical anisotropic bodies and the orientation direction thereof is limited to the y-axis direction, the effect of the present invention is not particularly limited to this configuration. It may be a negative optical anisotropic body, and the optical axis of the birefringent layer may be aligned with the y-axis direction. Similar to the above, the primary polarized light and the secondary polarized light are transmitted as light traveling at an angle θ with respect to each other except that the polarization direction of the primary polarized light traveling straight through the diffraction grating or the bending direction of the secondary polarized light (diffracted light) is different. It can be emitted separately.

Further, the polarization separation element has an advantage that the polarization separation angle can be easily controlled. That is, the diffraction grating 1
The angle θ formed by the separated primary polarized light and secondary polarized light can be arbitrarily set by changing the grating pitch D of 02 and 112. This is extremely preferable because it increases the degree of freedom in designing the optical system after the polarization separation element.

Further, in the above embodiment, the case where the incident light is made incident from the substrate side of the diffraction grating has been described, but the same action and effect can be obtained by making the incident light incident from the birefringent layer side.

(Embodiment 1 of Projection Display Device) The first embodiment of the projection display device of the present invention will be described below (FIG. 5).
Will be described using.

The projection display device of the present invention is basically a lamp 121, a parabolic mirror 122, a polarization separation element 123, a first lens array 124, a second lens array 125, a field lens 126, a liquid crystal panel 127, Projection lens 1
28. A retardation plate 129 is partially attached to one surface of the second lens array 125. In order to facilitate the explanation, we introduced a Cartesian coordinate system similar to (Fig. 3),
the x-axis is the optical axis direction along the rotational symmetry axis of the parabolic mirror 122,
Let the z-axis be the direction orthogonal to the paper surface.

The liquid crystal panel 127 is formed by sandwiching a twisted nematic liquid crystal generally used for this purpose between glass substrates having a pixel structure, and has polarizing plates 127A and 127B on the incident side and the emitting side thereof. For convenience, the transmission axis of the incident side polarization plate 127A (the vibration direction of the electric field of the light to be transmitted)
Is in the z-axis direction. A video signal is supplied to the liquid crystal panel 127 from the outside, and an optical image is formed by a two-dimensional pixel structure. The optical image is projected on the screen by the projection lens 128 to present a large screen image.

The polarization separation element 123 is, for example, the one shown in the first embodiment of the polarization separation element of the present invention (FIG. 3).
It is configured as follows. A saw-toothed diffraction grating 123A periodically formed in the y-axis direction and a positive uniaxial optical anisotropic body 123B oriented in the z-axis direction are appropriately formed.

The first lens array 124 is formed by arranging a plurality of first lenses 131 two-dimensionally, and an example of the configuration is shown in FIG. Regarding the Cartesian coordinate system introduced in (FIG. 5), the correspondence is shown in (FIG. 6). This is an array of 18 first lenses 131 inscribed in the cross section of the light flux of a perfect circle emitted from the parabolic mirror 122. The center of each optical axis of the first lens 131 is 131A, and all the lenses are appropriately decentered.

The second lens array 125 is formed by arranging a plurality of second lenses 135 two-dimensionally, and an example of the configuration is shown in (FIG. 7) similarly to (FIG. 6). Second lens 135
In the same manner, the same number is similarly arranged corresponding to the first lens 131. Each of the second lenses 135 has a corresponding first
The aperture of the lens 131 and the display area of the liquid crystal panel 127 are made to be conjugate with each other, and the light fluxes passing through the respective lenses are guided onto the panel in a superimposed form.

A retardation plate 129 is selectively and appropriately affixed to approximately half the area of each second lens 135. The retardation plate 129 is used to rotate the plane of polarization of the incident light by about 90 degrees, and for the wavelength λ representing the passing light, λ
A phase difference plate of / 2 may be used. The optical axis is selected in an appropriate direction so as to perform the operation described below. In this embodiment, the direction 136 rotated by 45 degrees from the y-axis direction to the z-axis direction.
And the optical axis directions of the retardation film 129 are made to coincide with each other.

By the action of the polarization separation element 123, the secondary polarized light 142 advances with respect to the primary polarized light 141 by a predetermined angle θ in the y-axis direction, and enters the first lens array 124. For one second lens 135, the phase difference plate 129
The region without is the aperture region for the primary polarization 141,
Its center of gravity is 135A. The region where the retardation plate 129 is present is an aperture region for the secondary polarization 142, and its center of gravity is 125B.

The optical axis center 131A of the first lens 131 may be determined so that the converged primary polarized light 141 'passes near the center of gravity 135A. Further, the converged secondary polarized light 142 ′ passes through a position on the aperture of the second lens 135, which is displaced by a predetermined distance in the y-axis direction. Polarization separation angle θ
By properly selecting, the passing position of the converged secondary polarized light 142 ′ can be made to be in the vicinity of the center of gravity 135B.

The naturally polarized light emitted from the lamp 121 is split by the polarization splitting element 123 into primary polarized light 141 in which the vibration direction of the electric field is the z-axis direction and secondary polarized light 142 in the y-axis direction. These are lights that travel at θ with respect to each other in the y-axis direction and enter the first lens array 124. The light converged by the first lens array 124 is
A discrete illumination spot is formed on the aperture of the second lens array 125, and according to the above configuration, the phase difference plate 129 is not selectively inserted only in the passing region of the secondary polarized light. Direction. Since the polarization planes of the primary polarized light 141 ″ and the secondary polarized light 142 ″ reaching the incident side polarization plate 127A are both in the z-axis direction, they pass through the polarization plate and illuminate the liquid crystal panel 127. Is effectively used as.

According to the above structure, since the light of the secondary polarized light which has been conventionally absorbed and lost by the incident side polarizing plate can be effectively used, it is possible to realize a projection type display device having high light utilization efficiency,
A bright projected image can be provided.

The polarization separation element 123 used in the projection display device is composed of a diffraction grating and a birefringent optical layer appropriately configured. Since the required thickness of the birefringent optical layer is extremely thin, about several microns, a liquid crystal polymer is used. It is possible to favorably orient a uniaxial optically anisotropic substance.

The path of the illuminating light is divided into the first-order polarized light and the second-order polarized light.
The parabolic mirror 1 has almost the same optical path length for the second polarization.
Most of the light condensed by 22 is the first lens array 124.
To the liquid crystal panel 1 through the second lens array 125.
Since it reaches 27, high light utilization efficiency can be realized for both the primary polarized light and the secondary polarized light. This makes it possible to realize a polarization conversion optical system that is highly effective in improving brightness.

(Third Embodiment of Polarization Separation Element) A third embodiment of the polarization separation element will be described with reference to FIG. The polarization beam splitting element 151 is configured so as to exert the following special effects when used in the projection display device as shown in FIG.

FIG. 8 is a front view of the polarization beam splitting element 151, and its sectional configuration is the same as that of the first or second embodiment of the polarization beam splitting element of the present invention.
However, a plurality of diffraction gratings 151 constituting the polarization separation element
A is arranged two-dimensionally. In addition, each diffraction grating 15
The effective area of 1A has a rectangular opening, and the diffraction pitch is appropriately made different in each area. A positive optical anisotropic layer oriented in a uniaxial direction is brought into close contact with the surfaces of these arrayed diffraction gratings, the primary polarized light goes straight, and the secondary polarized light is diffracted to separate incident light. The wavy line hatching in the rectangular aperture in FIG. 8 is added to schematically show that the periodic pitch of the diffraction grating in each rectangular aperture region differs depending on the location.

The polarization separation element 151 can be embodied according to the following procedure, for example. First, a plurality of diffraction gratings having different periodic pitches are formed according to the type of polarization separation angle required. The specific structure is the same as that shown in FIG. 3 or FIG. 4, and a matrix-shaped mother die to be embodied is formed by mechanical precision processing, a photolithography process, or the like. These master molds are cut out in a given rectangular opening shape, and a plurality of them are appropriately arranged to form a combined mold. A transparent resin material or the like is press-molded using this as a matrix to obtain a diffraction grating substrate of the polarization separation element 151. The diffraction grating surface may be subjected to rubbing treatment or a forcing force such as an electric field or a magnetic field to forcibly orient the uniaxial optical anisotropic body, and the state may be maintained by a method such as ultraviolet curing. Accordingly, the same elements as those of the first or second embodiment of the polarization splitting element of the present invention can be easily embodied in a two-dimensional array and the polarization splitting angles are appropriately changed.

The above structure is characterized in that the separation angles of the primary polarized light and the secondary polarized light emitted from the polarization separation element 151 are more preferably different depending on the location. The polarization splitting element configured in this way has the advantages of being able to realize an optical system with a higher degree of design freedom and a higher light utilization efficiency in a projection display device configured in combination with this.

(Second Embodiment of Projection Display Device) (FIG. 8)
Using the third embodiment of the polarization separation element of the present invention shown in
An example of a configuration that can achieve a greater effect when a projection display device similar to that of FIG. 5 is configured will be described.

FIG. 9 shows an example of the structure of the first lens array 161. 36 first lenses 161A having rectangular openings are two-dimensionally arranged. First lens 16
Each opening of 1A has a shape similar to the display area of the illuminated liquid crystal panel. The optical axis of the first lens 161A is appropriately decentered. With this configuration, the arrangement of the illumination spots formed by the first lenses on the second lens array can be adjusted relatively freely. FIG. 9 shows that when the number of lenses is increased as compared with the configuration shown in FIG. 6, the uniformity of the brightness of the light illuminating the liquid crystal panel is improved and the light utilization efficiency can be increased. There are advantages.

As a reference, in the case of the conventional configuration using no polarization separation element, an example of the configuration of the second lens array 162 used in combination with the first lens array having the arrangement and aperture shape shown in (FIG. 9) ( Fig. 10). A plurality of illumination spots converged by the first lens array are formed on the openings of the second lens array 162. This corresponds to the real image 163 of the luminous body in the lamp, and an example of its size and distribution is schematically shown in FIG.

For the reasons described below, the openings of the second lenses 164 forming the second lens array 162 are appropriately made different according to the size of the real image 163 formed on the openings, and these are aggregated. The second lens arrays are arranged so that the effective aperture of the entire second lens array is made as small as possible.
Therefore, the eccentric direction and the eccentric amount of the corresponding first lens are determined according to the opening position of the corresponding second lens 164.

Referring to FIG. 5, the second lens array 12
If the irradiation angle of the light emitted from the liquid crystal panel 127 with respect to the liquid crystal panel 127 is equal to or smaller than the converging angle of the projection lens 128, light that cannot effectively pass through the projection lens occurs.
Light loss occurs. Therefore, it is preferable that the effective aperture of the second lens array viewed from the liquid crystal panel is as small as possible. This is to make the irradiation angle of the illumination light passing through the liquid crystal panel as small as possible.

For this reason, the aperture shape of the second lens array 162 and the arrangement of the plurality of real images l63 shown in FIG. 10 are convenient. A perfect circle 165 indicated by a wavy line is a more preferable example of the converging range of the projection lens, which is drawn on the second lens array. The perfect circle 165 can be regarded as the entrance pupil of the projection lens, and the real image 163 can be treated as the size and distribution of the real images of the plurality of light emitters on the entrance pupil. Here, if the ratio of the sum of the spreads (areas) of the plurality of real images 163 to the spread (area) of the entrance pupil is taken as the pupil usage rate, the higher the pupil usage rate is, the higher the optical system of the projection display device becomes. It can be said that it is a brighter and preferable optical system.

In the projection type display device shown in FIG. 5, using the polarization separation element 151 shown in FIG. 8 is extremely effective in realizing an optical system with a high pupil utilization rate. . Specifically, FIG. 11 shows an example of the configuration of the second lens array 171 used in combination with the polarization separation element 151 shown in FIG. 8 and the first lens array 161 shown in FIG. State the reason.

The second lens array 171 is formed by aggregating the second lenses 172 having different sizes and shapes of apertures in the effective area of the perfect circle 173. A retardation plate for rotating the polarization plane of the secondary polarized light passing through the region by 90 degrees is attached to approximately a half region (illustrated by hatching for convenience) divided by the wavy line of each second lens 172. Numbers (1) to (36) are added to the first lens array 161 of (FIG. 9) and the second lens array 171 of (FIG. 11) in order to clarify the correspondence between the lenses.

The configuration of the second lens array 171 is the second
The first lens array is formed so that the size of the real image formed on the lens 172 is larger in the vicinity of the optical axis and smaller in the vicinity of the optical axis, so that the pupil utilization rate becomes larger. Are arranged, and corresponding lens aperture shapes and arrangements are formed. In this case, an example of the size and distribution of the real image formed on the second lens array 171 is the same as (FIG. 10) (FIG. 12).
It will be schematically described in the inside.

The 36 real images 175 shown by the solid lines are the first
It is an illumination spot for the primary polarization component that passes through the lens array. Each real image 175 is arranged such that it is arranged at the corresponding position of the opening of the corresponding second lens.
61A is appropriately eccentric.

The real image 176 shown by the broken line is an illumination spot for the secondary polarization component as well. These real images 1
Due to the action of the polarization separation element 151, the reference numeral 76 is formed so as to deviate from the real image 175 of the primary polarized light by a predetermined distance in a predetermined direction. However, if the aperture shape and arrangement of the second lens 172 are changed to improve the pupil utilization rate,
For each pair of the first lens and the second lens, the polarization separation angles of the primary polarized light and the secondary polarized light passing through the first lens need to be appropriately different. It is necessary to appropriately determine the polarization separation angle according to the distance between the real image 175 and the real image 176 to be shifted on the second lens array 171.

The polarization separation element 151 shown in FIG. 8 is
The first lens array 16 is constructed for the above reason.
For each corresponding first lens 161A on No. 1, the polarization separation angle of the two polarized lights that pass through the lens in the vicinity thereof can be easily made different as appropriate. Since the polarization separation element 151 is formed by combining diffraction gratings, there is an advantage that the polarization separation angle can be easily controlled only by appropriately changing the diffraction pitch in each rectangular region.

Concretely, the effect of the present invention will be described by using a numerical value based on a design example. In the second embodiment of the projection display device of the present invention, the optical path length from the second lens array to the liquid crystal panel is fixed, and the size of the effective aperture of the second lens array and the pupil utilization efficiency will be described.

In the case of the conventional structure not using the polarization separation element shown in FIG. 10, in order to utilize the light emitted from the expanded real image 163 without loss, the entrance pupil of the projection lens has the size of the broken line 165. Is necessary, which is equivalent to F / 2.5 when converted to F number. In this case, the real image 16
The pupil utilization rate was about 33% as a ratio of the total of the spreads (areas) of 3 to the area of the entrance pupil (a perfect circle having a radius of 165).

In the configuration using the polarization splitting element of the present invention shown in FIG. 12, the entrance pupil of the projection lens is a perfect circle 177 in order to utilize the light emitted from the spread real images 175 and 176 without loss. Is required, which is equivalent to F / 2.3 in terms of F number. In this case, the pupil utilization rate was about 57%.

Comparing the two, according to the present invention, the pupil utilization factor is improved to about twice and the components of both the primary polarized light and the secondary polarized light are A sufficiently high light utilization efficiency can be realized. This is because it is not necessary to increase the diameter of the projection lens, so that an optical system with a lower cost can be realized. Alternatively, since it is not necessary to use a lamp having a smaller light emitter, a brighter and more reliable lamp can be used to realize a brighter projection display device.

As a result, the polarization separation element of the present invention,
The projection type display device using this has a high light utilization efficiency and provides a bright projected image, and therefore an extremely large effect is obtained.

[0104]

The polarization splitting element of the present invention is a combination of a diffraction grating and a uniaxial optical anisotropic body, so that the construction is simple, the polarization splitting efficiency is high, and the polarization splitting angle is easy to control.
There is an advantage. Also, since the thickness of the optically anisotropic substance is as thin as several microns, it is possible to easily and satisfactorily orient and fill uniaxial anisotropic substances such as liquid crystal polymers, and easily achieve the desired device with high mass productivity. it can.

Further, the projection display apparatus of the present invention can provide a bright projected image with little display unevenness by using the polarization splitting element of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a general operation of a diffraction grating.

FIG. 2 is a schematic diagram for explaining a general operation of another diffraction grating.

FIG. 3 is a schematic configuration diagram showing an embodiment of a polarization beam splitting element of the present invention.

FIG. 4 is a schematic configuration diagram showing an embodiment of another polarization separation element of the present invention.

FIG. 5 is a schematic configuration diagram showing an embodiment of a projection display device of the present invention.

FIG. 6 is a schematic configuration diagram showing an example of the configuration of a first lens array.

FIG. 7 is a schematic configuration diagram showing an example of the configuration of a second lens array.

FIG. 8 is a schematic configuration diagram showing an embodiment of still another polarization separation element of the present invention.

FIG. 9 is a schematic configuration diagram showing another example of the configuration of the first lens array.

FIG. 10 is a schematic configuration diagram showing an example of a conventional configuration of a second lens array.

FIG. 11 is a schematic configuration diagram showing another example of the configuration of the second lens array.

FIG. 12 is a schematic diagram showing an example of a real image of a light-emitting body formed on a second lens array.

FIG. 13 is a schematic configuration diagram showing an example of a conventional projection display device.

FIG. 14 is a schematic configuration diagram showing an example of a conventional polarization separation element.

[Explanation of symbols]

101,111,123,151 Polarization separation element 102,112 diffraction grating 103,113 Uniaxial optical anisotropic body 121 lamp 122 Parabolic mirror 124,161 First lens array 125,171 Second lens array 126 field lens 127 LCD panel 128 projection lens 129 Phase plate

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Claims (3)

(57) [Claims] 1. A polarization separation element for separating incident natural light into an A-polarized light component having an oscillation component of an electric field in an azimuth A and a B-polarized component having an oscillation component of an electric field in an azimuth B orthogonal to the azimuth A, and emitting the separated components. The polarization splitting element is configured by arranging a plurality of units of polarization splitting elements in a two-dimensional array, and one unit of the polarization splitting element has a predetermined amount of light of the A-polarized component and light of the B-polarized component. A first lens having a perfect circular shape, which forms a predetermined separation angle in a direction and emits light in different traveling directions, and is combined with the polarization separation element.
The second lens array with respect to the array and the second lens array
Is an aperture shape and array that improves the pupil utilization rate.
Formed by the A-polarized light on the second lens array
The distance between the real image and the real image formed by the B-polarized light
Correspondingly, a plurality of the polarization separating elements arranged in a two-dimensional array
A polarization splitting element, wherein the polarization splitting angle is made different depending on the arrangement location . Wherein said polarization separation element is uniaxial direction C along the surface of a transparent substrate which is disposed substantially perpendicular to the optical axis of the incident light
A diffraction grating having a periodic structure in the optical axis, and an optical anisotropic layer formed adjacent to the diffraction grating, the optical anisotropic layer being on the surface of the substrate in the direction C.
Refractive index (N2) and the refractive index (N
1) have different refractive indices from each other, refraction of the diffraction grating
The index (N0) is chosen to be approximately equal to the index of refraction (N1) in direction D.
As a result , only one of the A-polarized component and the B-polarized component is selectively acted on the optical axis of the incident light to diffract the light of the polarized component by a predetermined angle. And the separation angle of the polarization separation element is changed by changing the pitch of the periodic structure of the polarization separation element.
The aperture shape and arrangement of the second lens array combined with
The polarization splitting element according to claim 1 , wherein the polarization splitting elements are made different from each other . 3. A light source that emits natural light, a condensing unit that condenses the light emitted from the light source to form light that travels in a substantially uniaxial direction, and a polarized light to which the light emitted from the condensing unit is incident. A separation element, a first lens array arranged in the vicinity of the polarization separation means, a second lens array on which the light emitted from the first lens array enters, and a second lens array arranged in the vicinity of the second lens array. Polarization plane rotating means for selectively acting on a part of the light passing through the lens array, spatial light modulation element irradiated with the light emitted from the second lens array, and an optical image on the spatial light modulation element. A projection lens for projecting, the spatial light modulation element acts on linearly polarized light to form the optical image, and the first lens array is formed by arranging a plurality of first lenses two-dimensionally, The second lens The ray is formed by arranging a plurality of second lenses that form a pair with the first lens in a two-dimensional array, the polarization separation element is the polarization separation element according to claim 1 , and the polarization separation element corresponds to the corresponding polarization separation element. The polarization separation angles are made different according to the position of the first lens, and the light of the A polarization component and the light of the B polarization component having different traveling directions are adjacent to different positions of the opening of the corresponding second lens by the first lens. The polarization plane rotating means selectively acts only on the light of one polarization component on the aperture of the second lens to rotate the polarization plane of the light of the polarization component by about 90 degrees. A projection display device characterized in that the polarization plane of the light of the A-polarized component and the polarization plane of the light of the B-polarized component applied to the spatial light modulator are substantially matched and used.