JPH10197827A - Polarized light separating element and projection type display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a thin-shaped high-efficiency polarized light separating element by constituting the polarized light separating element of a diffraction grating and an optical anisotropic layer formed adjacent to the diffraction grating. SOLUTION: This polarized light separating element 101 is constituted of the diffraction grating 102 and a double refraction layer 103. The diffraction grating 102 is formed by using an isotropic transparent substrate whose refractive index is N0. The double refraction layer 103 is constituted by orienting the positive uniaxial optical anisotropic body so that the optical axis may be aligned with the (z)-axis direction. As for the double refraction layer 103, the refractive index is N1 in the (z)-axis direction and the refractive index is N2 in an (y)-axis direction, and N1>N2 is established. In the case of selecting so that N0≈N1 may be satisfied, the first-order polarized light 104A out of the incident light 104 goes straight through the polarized light separating element 101 as it is, then, the light 104A is emitted. Since N0>N2 is established, the diffraction grating 102 works on the second-order polarized light 104B, then, the second order polarized light 104B is diffracted and emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a polarization separation element used mainly for illuminating a spatial light modulation element utilizing the polarization of light, and a projection display device using the polarization separation element.

[0002]

2. Description of the Related Art Conventionally, a CRT has been used as a projection display apparatus 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 transmission type liquid crystal panel using twisted nematic liquid crystal is known, and it is easy to miniaturize the projector, and a high definition image is projected by using a panel with a large number of pixels. It has been widely put to practical use because it can be used and mass-production technology for liquid crystal panels has been established for direct viewing.

[0003] Twisted nematic liquid crystal uses the polarization of light, and thus such a spatial light modulator has polarizers on the incident side and the output side. Of the light that illuminates the spatial light modulator, spatially changes the polarization state of linearly polarized light that has passed through the polarizer on the incident side, and controls the amount of light that passes through the polarizer on the output side to form an optical image. I 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 the polarization of light, the polarizer on the incident side transmits only about half of the natural light emitted by the lamp, and the other light is reflected or absorbed and lost. .

On the other hand, various techniques called polarization conversion have been proposed. This is because natural light of a light source is separated into light of a required polarization component and light of a polarization component orthogonal to the light in advance, and the polarization plane of the polarization component light that cannot be used as it is is rotated by 90 degrees to produce two lights. After the polarization planes are aligned, they are supplied to a spatial light modulator, and these are used.

Therefore, a projection type display device using polarization conversion includes a polarization splitting element for splitting natural light into two polarized light components having polarization directions orthogonal to each other, and a polarization plane of one of the separated polarized light beams. It is necessary to provide a polarization plane rotation element for rotating the polarization plane. As the polarization separation element, a polarization separation multilayer film utilizing Brewster's angle and interference is widely known, and there are a plate type and a prism type polarization separation element.

On the other hand, a phase film called a λ / 2 plate is generally known as a polarization plane rotating element. This is an optically transparent organic film stretched uniaxially to give it an optical anisotropy. The thickness and optical anisotropy are controlled and the transmitted light is equivalent to half the wavelength λ. This gives 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 becomes linearly polarized light with the plane of polarization rotated by 90 degrees.

[0009]

None of the conventionally proposed configurations of polarization conversion or the optical systems used therefor achieve satisfactory 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 this is rotated before the polarization plane is rotated. Is called secondary polarization. An optical path through which the primary polarized light passes is defined as a primary optical axis, and
The optical path through which the secondary polarized light passes is defined as a secondary optical axis.

In order to realize the polarization conversion, the light use efficiency of the entire optical system must be sufficiently high for both the primary polarized light and the secondary polarized light. When the primary conversion efficiency is greatly reduced by using the polarization conversion as compared with the case where the polarization conversion is not used, the original purpose of increasing the light use efficiency due to the introduction of the polarization conversion is reduced and the brightness is improved. Not enough.

Further, the secondary polarization must not increase uneven brightness or color of light illuminating the spatial light modulator. There is a problem because the illumination unevenness of the illumination light causes uneven brightness and color of the projected image.

[0013] Further, means for realizing polarization conversion are those which significantly increase the optical path length of primary polarized light and secondary polarized light, those which greatly increase the size of the optical system, and those which significantly increase the cost of the optical system. Don't be. Problems such as an increase in light loss in a long optical path, an increase in the size of the projection display device, and an increase in cost are caused.

For the above reasons, conventional polarization conversion techniques are disclosed in JP-A-3-13983 and JP-A-4-6331.
8, JP-A-4-177335, JP-A-5-177
No. 27203 and JP-A-7-64075 are not sufficient. Both use a prism on which a polarization separation multilayer film is deposited, so the polarization separation element is expensive, large, increases the optical path length of primary polarized light and secondary polarized light, and the optical path length from the light source to the spatial light modulator. However, there is a problem that the primary polarized light and the secondary polarized light are greatly different from each other, 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 primary polarized light and secondary polarized light. The conditions for collecting, transmitting, and illuminating the light emitted from the light source can be the same for both the primary polarized light and the secondary polarized light. This means that the light use efficiency of the light in both polarization directions should be high, the uniformity of the illumination light should be the same,
This is preferred because it becomes easier. It is possible to provide a projection image which is bright and has little display unevenness.

On the other hand, the polarized light separating element disclosed in Japanese Patent Application Laid-Open No. Hei 3-174502 has a structure in which a uniaxial birefringent material whose optical axes are aligned is sandwiched between two prisms. Only one of them is selectively totally reflected to separate polarized light. Although this is excellent in heat resistance and polarization separation efficiency, it is expensive because the polarization separation element is large and a glass prism on a bulk is used. Further, there is a problem because the length of the optical path that acts is long.

The optical system disclosed in Japanese Patent Application Laid-Open No. 4-234016 has the same optical path length from the light source to the spatial light modulator for primary polarized light and secondary polarized light. This is preferable in that both polarized lights are handled under the same conditions, but the configuration disclosed in the 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 Patent Application Laid-Open No. 6-202094 discloses an example of an optical system that can use both primary polarized light and secondary polarized light by using a thin polarization separation element. . The configuration of this optical system is shown in FIG.

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

Reference numeral 903 denotes a polarization splitting element, an example of which is shown in FIG. This causes the primary polarized light and the secondary polarized light to be emitted as light whose traveling directions differ by an angle θ. As a result, the spot of the light beam that the first lens array 904 converges on the opening of the second lens array 905 is shifted 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 opening 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 the plane of polarization by 90 degrees, and the light emitted from the second lens array 905 The planes of polarization of the secondary polarized light and the secondary polarized light are aligned in the same direction. If this is made to correspond to the polarization direction of the incident-side polarizing plate of the liquid crystal panel 907, an optical system with high light use efficiency can be realized.

An example of the configuration of the polarization separation element 903 will be supplemented. Reference numeral 911 denotes a sawtooth-shaped prism array substrate, 912 denotes a plane substrate, and 913 denotes a birefringent optical material layer, and a liquid crystal layer, an organic film, a monomer, and the like can be used. Combining a prism layer made of a birefringent material adjacent to a prism whose refractive index is isotropic, and changing the condition of refraction at the prism interface for orthogonal polarization directions,
Separating two polarized lights so that the traveling directions are different from each other is widely known as a Wollaston prism. The polarized light separating element 903 is an array of the polarized light separating elements 903, and generally uses expensive calcite as a birefringent material by using an organic material such as a liquid crystal or a monomer in a uniaxial direction. .

Although the above-described operation can be obtained in principle, the polarization beam splitter 903 actually has the following problems. Since the liquid crystal and the organic film are relatively weak to heat, there is a problem in using the liquid crystal or the organic film arranged near a light source emitting high heat.

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. Birefringent molecules such as liquid crystals are converted into magnetic fields, electric fields,
It is widely known that the film can be uniaxially oriented by rubbing or the like, but generally it can be oriented at most to a thickness of several tens of microns. The methods and materials used are not widely known. Regarding this point, see JP-A-6-20
No. 2094 is not disclosed.

Therefore, the polarizing beam splitter having the above structure and the projection display device using the same have a serious problem in realizing a polarizing beam splitter having a desired function.

Further, JP-A-8-234205 discloses that
In view of the above, a configuration is disclosed in which a polarization-selective mirror composed of a multilayer film is combined with a bulk prism as a polarization separation element. An example of a method of configuring a thin polarization separation element by arranging small polarization selective prisms in an array has also been disclosed.

However, each of these methods has a problem that a long optical path length is required for disposing the prism, the prism is expensive, and the configuration of the prism array is complicated and 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 which is relatively easy to realize. Further, it is another object of the present invention to provide a projection display device that provides a bright display image with high light use efficiency by using the polarization separation element.

[0028]

In order to solve the above-mentioned problems, a first polarization splitting element of the present invention converts an incident natural light into an A-polarized component having an electric field vibration component in an azimuth A, and an A-polarized component. A polarization splitting element for separating and emitting a B-polarized component having an electric field vibration component in an orthogonal azimuth B, and comprising: a light-transmitting substrate disposed substantially orthogonal to an optical axis of incident light; A diffraction grating having a periodic structure in a uniaxial direction C, and an optically anisotropic layer formed adjacent to the diffraction grating, and the optically anisotropic layer is formed on the substrate surface in a direction C and a direction D orthogonal thereto. And the diffraction grating has
Only one of the A-polarized component and the B-polarized component acts selectively to diffract the light of the polarized component by a predetermined angle, and the light of the A-polarized component and the light of the B-polarized component move in the traveling direction of each other. These are emitted as different lights.

Further, in order to solve the above problems, a first projection type display device according to the present invention comprises a light source which emits natural light,
A light condensing means for condensing the light emitted by the light source to form light traveling in a substantially uniaxial direction; a polarization separation element to which light emitted from the light condensing means is incident; and a light separation element disposed near the polarization separation element. One lens array, a second lens array on which light emitted from the first lens array is incident, and a polarization plane disposed near the second lens array and selectively acting on a part of light passing through the lens array Rotating means, second
A spatial light modulation element that is irradiated with light emitted from the lens array; and a projection lens that projects an optical image on the spatial light modulation element, wherein the polarization separation element is the first polarization separation element described above, The light modulating element 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 forms a pair with the first lens. A plurality of second lenses are two-dimensionally arranged, and the A-polarized light component and the B-polarized light component having different traveling directions are converged by the first lens at different positions of the corresponding openings of the second lens. The polarization plane rotating means selectively acts on only one of the polarized light components on the aperture of the second lens to rotate the polarized light plane of the polarized light component by approximately 90 degrees, and irradiates the spatial light modulator. Polarization plane of the A-polarized light component and B-polarized light It is obtained so as to take advantage of these and polarization of light allowed substantially coincide.

Further, in order to solve the above problem, the second polarization splitting element of the present invention converts an incident natural light into an A polarization component having an electric field vibration component in an azimuth A and an azimuth B component orthogonal to the azimuth A. A polarization separation element that separates and emits a B-polarization component having an electric field vibration component. The polarization separation element is configured by arranging a plurality of units of polarization separation elements in a two-dimensional manner. The unit is to cause the light of the A-polarized light component and the light of the B-polarized light component to emit at a predetermined separation angle in a predetermined direction so that the traveling directions are different from each other. It is to make them different.

Preferably, in the second polarization splitting element of the present invention, the polarization splitting element includes a light-transmitting substrate disposed substantially orthogonal to the optical axis of the incident light, and a uniaxial direction C along the substrate surface.
A diffraction grating having a periodic structure, and an optically anisotropic layer formed adjacent to the diffraction grating. The optically anisotropic layer has different refractive indices on a substrate surface in a direction C and a direction D orthogonal thereto. The diffraction grating selectively acts on only one of the A-polarization component and the B-polarization component to diffract light of the polarization component by a predetermined angle, and changes the pitch of the diffraction grating to change the diffraction grating pitch. This is to make the separation angles of the polarization separation elements different from each other appropriately.

Further, in order to solve the above problem, a second projection type display device according to the present invention comprises a light source which emits natural light,
A light condensing means for condensing light emitted from the light source to form light traveling substantially in a uniaxial direction; a polarization separation element to which light emitted from the light condensing means is incident; One lens array, a second lens array on which light emitted from the first lens array is incident, and a polarization plane disposed near the second lens array and selectively acting on a part of light passing through the lens array Rotating means, second
Equipped with a spatial light modulator that irradiates 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 arranged two-dimensionally. The separation element is the above-mentioned second polarization separation element of the present invention, and the polarization separation element varies the polarization separation angle according to the position of the corresponding first lens, and has different traveling directions from each other.
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 apertures of the second lens, and the polarization plane rotation means operates any one of the polarizations on the aperture of the second lens. Selectively act on the component light to rotate the plane of polarization of the polarized component light by approximately 90 degrees, thereby irradiating the spatial light modulator with the polarized plane of the A polarized component light and the B polarized component light. The wavefronts are substantially matched to use this.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that a polarization grating is formed by combining a diffraction grating and a uniaxial optically anisotropic layer. Prior to the specific description of the present invention, first,
The general public knowledge about the diffraction grating will be described.

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

Here, if the maximum height H [m] gives a phase difference of 2π to the light 12 of wavelength λ [m] incident from the normal direction of the substrate, almost all of the incident light 12 Are bent by the 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). Here, Ns is the refractive index of the diffraction grating substrate, and Na is the refractive index of the medium surrounding the diffraction grating.

[0037]

(Equation 1)

[0038]

(Equation 2)

FIG. 2 shows a configuration example of the diffraction grating 15 known as a binary optical element. This is an approximation of the saw-tooth microstructure of FIG. 1 with a step-like step structure. In this case, the number of levels of the flat portion of the stairs is called the number of levels, and the case where the diffraction grating 15 has seven levels is illustrated.

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 + 1st-order diffracted light 16 '. For height H and pitch D, (Equation 1), (Equation 2)
Holds similarly.

For example, if the number of levels is 2, 4, 8, 16
, The theoretical diffraction efficiency is 40.5
%, 81%, 95% and 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 splitter 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 description, an orthogonal coordinate system is introduced, a direction along the plane of the paper is an xy plane, a direction perpendicular to the plane of the paper is az axis, and the polarization separation element 101 is two-dimensionally arranged on a yz plane. It is assumed that the light ray 104 that spreads and is considered as a reference is incident along the x-axis.

For example, the diffraction grating 102 is the same as that shown in FIG. 1 and is formed by periodically forming a saw-toothed minute structure 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 optically anisotropic body so that its optical axis coincides with the z-axis direction. Regarding the birefringent layer 103, the refractive index in the z-axis direction is N1, the refractive index in the y-axis direction is N2,
It is assumed that N1> N2.

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

For example, the refractive index N of the substrate 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 polarized light 104A, and the primary polarized light 104A of the incident light 104 goes straight out of the polarized light separating element 101 and exits.

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

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

[0049]

(Equation 3)

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

For the above reason, two out of the incident light 104
Most of the secondary polarized light 104B is diffracted by + θ and emitted. That is, the polarization splitting element 101 converts the incident light 104
Acts 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 polarized light separating element of the present invention may be a polarized light separating element 111 shown in FIG. This uses the binary optical element shown in FIG. 2 instead of the diffraction grating 101 in FIG. An orthogonal coordinate system similar to that shown in FIG. 3 is introduced.

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

The primary polarized light 114A whose electric field oscillates in the z-axis direction does not receive the action of the diffraction grating 112 and travels straight through the polarization splitting element 111 and exits. On the other hand, the secondary polarization 114B whose electric field oscillates in the y-axis direction
Is diffracted by the diffraction grating 112 and emitted.

Also in this case, the maximum height H of the diffraction grating 112
Is selected such 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 splitting elements shown in FIGS. 3 and 4 use a diffraction grating, the birefringent layers 103 and 113 are used.
Is characterized by having a very small thickness. 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 also about the same. Therefore, it is extremely easy to fill liquid crystal molecules, liquid crystal monomers, liquid crystal polymers, uniaxial organic materials, and the like into the microstructure portion of the diffraction grating and orient them in a predetermined uniaxial direction. An excellent polarization separation element can be obtained.

In particular, when a diffraction element having a minute pitch is formed, the binary optical element is excellent in workability. A stepper exposure used in a semiconductor exposure apparatus is used to form a diffraction grating having a high processing accuracy, excellent mass productivity, low cost, and a relatively large area by combining processes of resist coating, pattern exposure, and etching. Therefore, the polarization splitting element shown in FIG. 2 is extremely easy to realize a diffraction grating, and can realize an element with higher mass productivity and lower cost.

Hereinafter, specific embodiments of the polarizing beam splitter and the projection display device of the present invention will be described with reference to the drawings and numerical examples.

(First Embodiment of Polarization Separation Element) As a first embodiment 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.
Isotropic transparent body. The birefringent layer 103 is formed by orienting a material having a positive birefringence such that the optical axis is aligned with the z-axis, and the refractive index in the z-axis direction is 1.6, which is the same as the refractive index of the diffraction grating. I do. Also, the refractive index in the y-axis direction orthogonal to this is 1.45.

The above configuration can be realized, for example, by curing appropriately formed organic molecules such as a liquid crystal polymer and a liquid crystal monomer in a state where they are forcibly aligned on the diffraction grating 101. Examples of the orientation means include rubbing 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 10A
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 Expression (1).
However, 550 nm having the highest visibility was selected as the reference wavelength λ.

In this case, the diffraction angle θ changes depending on the wavelength, but the 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 of blue light having a wavelength of 490 nm is 7.1 degrees, and the diffraction angle of light having a wavelength of 610 nm is 8.8 degrees.

In order to maximize the + 1st-order diffraction efficiency for the secondary polarized light 104B, the maximum height H of the diffraction grating is set to 3.67 μm from the equation (2). Thereby, with respect to the light having the reference wavelength of 550 nm, almost all the light of the secondary polarized light 104B is diffracted and separated in the direction of the angle θ. If the wavelengths are different, the diffraction efficiency decreases, but practically sufficient diffraction efficiency can be obtained in all visible wavelength bands.

(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 (1) can be applied to (FIG. 4) almost in the same manner. Thus, similarly to the first embodiment, for example, a polarization beam splitter having a polarization beam splitting angle of 8 degrees can be configured.

The practically sufficient diffraction efficiency can be obtained by setting the number of levels of the diffraction grating 112 to at least 4 or more, preferably about 8.

In the first and second embodiments, the birefringent layer 1
03 and 113 are defined as positive optical anisotropic bodies, and the orientation direction is limited to the y-axis direction. However, 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 coincide with the y-axis direction. The primary polarized light and the secondary polarized light are converted into light traveling at an angle θ to each other in the same manner as described above, except that the polarization direction of the primary polarized light or the bending direction of the secondary polarized light (diffracted light) that goes straight through the diffraction grating is different. It can be separated and emitted.

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

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

(Embodiment 1 of Projection Display Apparatus) Hereinafter, a first embodiment of the projection display apparatus of the present invention (FIG. 5)
It is described using.

The projection display apparatus of the present invention basically includes 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 adhered to one surface of the second lens array 125. In order to facilitate the explanation, we introduced a rectangular coordinate system similar to that shown in FIG.
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 perpendicular to the plane of the paper.

The liquid crystal panel 127 is obtained by sandwiching a twisted nematic liquid crystal generally used for this purpose by a glass substrate having a pixel structure, and includes polarizing plates 127A and 127B on the incident side and the exit side. For convenience, the transmission axis of the incident-side polarizing plate 127A (the vibration direction of the electric field of the transmitted light)
Is 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 a screen by the projection lens 128, so that a large screen image can be presented.

The polarization beam splitter 123 is, for example, the one shown in Embodiment 1 of the polarization beam splitter of the present invention (FIG. 3)
It is configured as follows. A sawtooth diffraction grating 123A periodically formed in the y-axis direction and a positive uniaxial optically anisotropic body 123B oriented in the z-axis direction are appropriately formed.

The first lens array 124 has a plurality of first lenses 131 arranged two-dimensionally, and an example of the configuration is shown in FIG. The correspondence of the rectangular coordinate system introduced in (FIG. 5) is shown in (FIG. 6). This is one in which 18 first lenses 131 are arranged so as to be inscribed in the cross section of a light beam 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 has a plurality of second lenses 135 arranged two-dimensionally, and an example of the configuration is shown in FIG. 7 as in FIG. Second lens 135
Are similarly arranged in the same number corresponding to the first lens 131. Each of the second lenses 135 has a corresponding first lens.
The opening of the lens 131 and the display area of the liquid crystal panel 127 are conjugated to each other, and the light beam passing through each lens is guided onto the panel in a superimposed form.

A phase difference plate 129 is selectively and appropriately affixed to approximately a half area of each second lens 135. The phase difference plate 129 is used to rotate the plane of polarization of the incident light by about 90 degrees, and the wavelength λ representing the passing light is λ
/ 2 retardation plate may be used. An appropriate direction of the optical axis is selected so as to perform the operation described later. In this embodiment, the direction 136 which is 45 degrees from the y-axis direction to the z-axis direction
And the optical axis direction of the phase difference plate 129 are matched.

By the operation of the polarization splitting element 123, the secondary polarized light 142 travels with a predetermined angle θ shifted in the y-axis direction with respect to the primary polarized light 141, and enters the first lens array 124. Regarding one second lens 135, the phase difference plate 129
The region without the mark is an opening region for the primary polarized light 141,
The center of gravity is set to 135A. The region where the phase difference plate 129 exists is an opening region for the secondary polarized light 142, and its center of gravity is 125B.

The center 131A of the optical axis of the first lens 131 is preferably determined so that the converged primary polarized light 141 'passes near the center of gravity 135A. In addition, the converged secondary polarized light 142 ′ passes through a position shifted by a predetermined distance in the y-axis direction on the opening of the second lens 135. The polarization separation angle θ
Is appropriately selected, the passing position of the converged secondary polarized light 142 ′ can be set near the center of gravity 135 </ b> B.

The naturally polarized light emitted from the lamp 121 is separated by the polarization separation element 123 into a primary polarized light 141 in which the electric field oscillates in the z-axis direction and a secondary polarized light 142 in the y-axis direction. These become light traveling at each θ 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 opening of the second lens array 125, and from the above configuration, the wavefront rotates by 90 degrees when the phase difference plate 129 is selectively inserted only in the region where the secondary polarized light passes, and the z-axis is rotated. Direction. Since the polarization planes of the primary polarized light 141 ″ and the secondary polarized light 142 ″ that reach the incident-side polarizing plate 127A are both in the z-axis direction, they pass through the polarizing plate and illuminate the liquid crystal panel 127. It is effectively used as

According to the above configuration, the light of the secondary polarization, which has been absorbed and lost by the incident-side polarizing plate, can be used effectively, so that a projection display device with high light use efficiency can be realized.
A bright projection image can be provided.

The polarization separating element 123 used in the projection display device is composed of a diffraction grating and a birefringent optical layer appropriately formed. Since the required thickness of the birefringent optical layer is as extremely small as about several microns, the liquid crystal polymer Such a uniaxial optical anisotropic body can be favorably oriented.

The path of the illumination light is the same as the primary polarization
For the second-order polarized light, the optical path lengths are almost equal, and the parabolic mirror 1
Most of the light condensed by the first lens array 124
To the liquid crystal panel 1 through the second lens array 125.
27, high light use efficiency can be realized for both primary polarized light and secondary polarized light. Thereby, a polarization conversion optical system having a high effect of improving brightness can be realized.

(Embodiment 3 of Polarization Separation Element) A third embodiment of the polarization separation element will be described with reference to FIG. The polarization separation element 151 is configured to exhibit the following special effects when used in a projection display device as shown in FIG.

FIG. 8 is a front view of the polarization beam splitter 151, and its cross-sectional configuration is the same as that of the above-described first or second embodiment of the polarization beam splitter of the present invention.
However, a plurality of diffraction gratings 151 constituting the polarization splitting element
A is two-dimensionally arranged. In addition, each diffraction grating 15
The effective area of 1A is a rectangular aperture, and the diffraction pitch is appropriately varied in each area. A positive optically anisotropic layer oriented in a uniaxial direction is adhered to the surface of these arrayed diffraction gratings, the primary polarized light goes straight, and the secondary polarized light is diffracted to separate incident light. In FIG. 8, the wavy hatching in the rectangular apertures is added to schematically show how the periodic pitch of the diffraction grating in each rectangular aperture area differs depending on the location.

The polarization separation element 151 can be embodied, for example, according to the following procedure. First, a plurality of diffraction gratings having different periodic pitches are formed according to the type of required polarization separation angle. The specific configuration is the same as that shown in (FIG. 3) or (FIG. 4), and a matrix having a lattice shape to be embodied is formed by mechanical precision processing, a photolithography process, or the like. These mother dies are cut out in a given rectangular opening shape, and a plurality of them are appropriately arranged to form a combined mold. By using this as a matrix and pressing a transparent resin material or the like, a diffraction grating substrate of the polarization separation element 151 is obtained. With respect to the diffraction grating surface, the uniaxial optically anisotropic body may be forcibly oriented by a rubbing process or a forced force such as an electric field or a magnetic field, and the state may be maintained by a method such as ultraviolet curing. Thus, the same elements as those of the first or second embodiment of the polarization splitting element of the present invention can be easily realized in a form in which the elements are two-dimensionally arranged and the polarization splitting angles are appropriately changed.

The above configuration is characterized in that the separation angle of the primary polarized light and the secondary polarized light emitted from the polarization separation element 151 is more preferably different depending on the location. The polarization splitting element configured as described above has an advantage that a projection display apparatus configured in combination therewith has a higher degree of freedom in design and can realize an optical system with higher light use efficiency.

(Second Embodiment of Projection Display Device) (FIG. 8)
Using the third embodiment of the polarization beam splitter of the present invention shown in FIG.
An example of a configuration capable of obtaining a greater effect when configuring a projection display device similar to that shown in FIG. 5 will be described.

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

For reference, in the case of the conventional configuration using no polarization splitting element, an example of the configuration of the second lens array 162 used in combination with the first lens array having the arrangement and the aperture shape shown in FIG. It is shown in FIG. A plurality of illumination spots converged by the first lens array are formed on the opening 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 added in (FIG. 10).

For the reason described below, the aperture of the second lens 164 constituting the second lens array 162 is appropriately varied according to the size of the real image 163 formed on the aperture, and these are aggregated. The arrangement is such that the spread of the effective aperture of the entire second lens array is made as small as possible.
For this purpose, 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
The irradiation angle of the light emitted from the liquid crystal panel 127 to the liquid crystal panel 127 is not equal to or smaller than the converging angle of the projection lens 128, and light that cannot effectively pass through the projection lens is generated.
This causes light loss. Therefore, it is preferable that the effective aperture of the second lens array as seen from the liquid crystal panel is as small as possible. This is to make the illumination angle of the illumination light passing through the liquid crystal panel as small as possible.

For this reason, the opening shape of the second lens array 162 and the arrangement of the plurality of real images 163 shown in FIG. 10 are convenient. A perfect circle 165 indicated by a wavy line shows a more preferable example of the condensing range of the projection lens on the second lens array. This 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, assuming that the ratio of the sum of the spread (area) of the plurality of real images 163 to the spread (area) of the entrance pupil is the pupil utilization rate, the optical system having a higher pupil utilization rate requires a projection-type display device. It can be said that this is a brighter and preferable optical system.

In the projection type display device shown in FIG. 5, the use of the polarization splitting element 151 shown in FIG. 8 has an extremely high effect in realizing an optical system having 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 beam splitter 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 and arranging second lenses 172 having different sizes and shapes in the effective area of a perfect circle 173. A phase difference plate for rotating the plane of polarization of the secondary polarized light passing through the area by about 90 degrees is attached to an approximately half area (for convenience, shown by hatching) separated by a wavy line of each second lens 172. In the first lens array 161 of FIG. 9 and the second lens array 171 of FIG. 11, numerals (1) to (36) are added to clarify the correspondence between the lenses.

The structure of the second lens array 171 is similar to that of the second lens array 171.
The first lens array is formed such that the size of the real image formed on the lens 172 is larger near the optical axis and smaller as the distance from the optical axis is smaller, so that the pupil utilization ratio is larger. Are arranged, and the corresponding aperture shapes and arrangements of the lenses are configured. 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 in FIG. 10 (FIG. 12).
It is schematically added in the inside.

The 36 real images 175 shown by solid lines are the first
This is an illumination spot for the primary polarization component passing through the lens array. Each real image 175 is placed at a corresponding position of the corresponding aperture of the second lens so that the first lens 1
61A is appropriately eccentric.

A real image 176 shown by a broken line is an illumination spot for the secondary polarization component. These real images 1
76 is formed by being shifted by a predetermined distance in a predetermined direction with respect to the real image 175 of the primary polarized light by the operation of the polarization splitting element 151. However, when 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, it is necessary to appropriately change the polarization separation angles of the primary polarized light and the secondary polarized light passing through the first lens. It is necessary to appropriately determine the polarization separation angle in accordance with 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.
The first lens array 16 is configured for the above reason.
For each of the corresponding first lenses 161A on 1, the polarization separation angles of the two polarized lights that are in the vicinity and pass through the lens can be appropriately and easily changed. 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.

Specifically, the effects of the present invention will be described using numerical values based on a design example. In the second embodiment of the projection display apparatus 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 configuration shown in FIG. 10 which does not use the polarization splitting element, the entrance pupil of the projection lens has a size of a broken line 165 in order to use the light radiated from the spread real image 163 without loss. , Which was equivalent to F / 2.5 in terms of F number. In this case, the real image 16
The pupil utilization rate was about 33% as a ratio of the total of the three spreads (areas) to the area of the entrance pupil (a perfect circle having a radius of 165).

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

A comparison of the two shows that the present invention improves the pupil utilization factor by about twice without increasing the converging angle of the projection lens so much that the primary and secondary polarized light components are A sufficiently high light use efficiency can be realized. This eliminates the need to increase the diameter of the projection lens, so that an optical system with lower cost can be realized. Alternatively, since it is not necessary to use a lamp with a smaller luminous body, a brighter projection display device can be realized by using a brighter and more reliable lamp.

As a result, the polarized light separating element of the present invention is
A projection type display device using the same has a high light use efficiency and provides a bright projection image, so that an extremely large effect is obtained.

[0104]

Since the polarization splitting element of the present invention is a combination of a diffraction grating and a uniaxial optically anisotropic body, the configuration is simple, the polarization splitting efficiency is high, and the polarization splitting angle can be easily controlled.
There is an advantage. In addition, since the thickness for orienting the optical anisotropic body is as thin as several microns, a uniaxial anisotropic body such as a liquid crystal polymer can be easily and well aligned and filled, and the desired element can be easily realized with high mass productivity. it can.

Further, the projection type display device of the present invention can provide a bright projected image with less display unevenness by using the above-mentioned polarization splitting element of the present invention.

[Brief description of the 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 the polarization beam splitter of the present invention.

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

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

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

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

FIG. 8 is a schematic structural view showing still another embodiment of the polarization beam splitter 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 view 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 illustrating 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 Liquid crystal Panel 128 Projection lens 129 Phase difference plate

Claims (5)

[Claims] 1. A polarization splitting element for separating incident natural light into an A-polarized component having an electric field vibration component in an azimuth A and a B-polarized component having an electric field vibration component in an azimuth B orthogonal to the azimuth A and emitting the same. A translucent substrate disposed substantially orthogonal to the optical axis of the incident light, a diffraction grating having a periodic structure in a uniaxial direction C along the substrate surface, and formed adjacent to the diffraction grating. The optical anisotropic layer has different refractive indices on the substrate surface in the direction C and a direction D orthogonal thereto, and the diffraction grating has
The A-polarized component or the B-polarized component selectively acts on only one of the polarized components to diffract the light of the polarized component by a predetermined angle, and the light of the A-polarized component and the light of the B-polarized component are A polarized light separating element, which emits them as light having different traveling directions. 2. A light source for radiating natural light, a light condensing means for condensing light emitted from the light source to form light traveling in a substantially uniaxial direction, and a polarized light on which light emitted from the light condensing means is incident. A separating element, a first lens array disposed near the polarization separating element, a two-lens array on which light emitted from the first lens array enters, and a lens disposed near the second lens array. Polarization plane rotating means for selectively acting on a part of light passing through the array, a spatial light modulation element irradiated with light emitted from the second lens array, and projecting an optical image on the spatial light modulation element A polarization lens, wherein the polarization beam splitting element is the polarization beam splitting element according to claim 1, wherein the spatial light modulation element acts on linearly polarized light to form the optical image;
The 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 arranged two-dimensionally. The light of the A-polarization component and the light of the B-polarization component, which are different from each other, are converged by the first lens at different positions of the corresponding apertures of the second lens. Only one polarization component of the light is selectively actuated to change the polarization plane of the polarization component of the light by approximately 90 degrees.
A, and the A is irradiated on the spatial light modulator.
A projection display device, wherein the polarization plane of the polarization component light and the polarization plane of the B-polarization component light are substantially matched to each other and used. 3. A polarization splitting element for separating incident natural light into an A-polarized component having an electric field vibration component in an azimuth A and a B-polarized component having an electric field vibration component in an azimuth B perpendicular to the azimuth A and emitting the same. Wherein the polarization beam splitting element is configured by arranging a plurality of units of polarization beam splitting elements in a two-dimensional manner, and one unit of the polarization beam splitting element is configured such that the light of the A polarized light component and the light of the B polarized light component are predetermined. A polarized light separating element, which emits light so that the traveling directions are different from each other at a predetermined separating angle in the direction, and the polarized light separating angle is different for at least one of the polarized light separating elements. 4. A polarization-separating element comprising: a light-transmitting substrate disposed substantially orthogonal to an optical axis of incident light; a diffraction grating having a periodic structure in a uniaxial direction C along the substrate surface; And an optically anisotropic layer formed adjacent to the optically anisotropic layer, the optically anisotropic layer has a different refractive index on the substrate surface in the direction C and a direction D perpendicular thereto, and the diffraction grating , Selectively act on only one of the A-polarized component or the B-polarized component to diffract light of the polarized component by a predetermined angle, and vary the pitch of the diffraction grating to change the polarization separation element. 4. The polarization splitting device according to claim 3, wherein the splitting angles are appropriately varied. 5. A light source for radiating natural light, a condensing means for condensing light emitted from the light source to form light traveling in a substantially uniaxial direction, and a polarized light on which light emitted from the condensing means is incident. A separating element, a first lens array arranged near the polarization separating means, a second lens array on which light emitted from the first lens array is incident, and a second lens array arranged near the second lens array. Polarization plane rotating means for selectively acting on a part of light passing through the lens array, a spatial light modulator to which light emitted from the second lens array is irradiated, and an optical image on the spatial light modulator. A projection lens for projecting, the spatial light modulator acts on linearly polarized light to form the optical image, and the first lens array has a plurality of first lenses arranged two-dimensionally, The second lens The ray is configured by two-dimensionally arranging a plurality of second lenses forming a pair with the first lens, wherein the polarized light separating element is the polarized light separating element according to claim 3, and the polarized light separating element is the corresponding polarized light separating element. The polarization separation angles are made different according to the position of the first lens, and the light of the A-polarized light component and the light of the B-polarized light component having different traveling directions are adjacent to the different positions of the openings of the second lens corresponding to the first lens. The polarization plane rotating means selectively acts on only one of the polarized light components on the aperture of the second lens to rotate the polarized light plane of the polarized light component by approximately 90 degrees. A projection display device, wherein the polarization plane of the A-polarized component light applied to the spatial light modulator is made substantially coincident with the polarization plane of the B-polarized component light and is used.