JPH095778A - Spatial optical modulation element - Google Patents

Abstract

PURPOSE: To provide a spatial optical modulation element which suppresses the degradation on a peripheral contrast in the case where a high-luminance region exists in part of input images. CONSTITUTION: This spatial optical modulation element includes two sheets of glass substrates 2 which hold an optical modulation layer 8, a light reflection layer 5 and a photoconductive layer 4, a light transparent plate 9 which is fixed to the glass substrate surface on the photoconductive layer side and at least one kind of translucent media 10 which are arranged between the glass substrate 2 and the light transparent plate 9. At least the partial region of the surface of the light transparent plate 9 far from the glass substrate 2 is a concave surface. The element includes a light absorptive material 11 in the region where the effective luminous flux of the light transparent plate 9 does not pass and an antireflection film 12 in the region where the effective luminous flux passes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator used for a large screen television or the like.

[0002]

2. Description of the Related Art In recent years, a projection type display using a spatial light modulator in which a photoconductive layer and a light modulating layer are combined has been actively developed (Technical Report of the Television Society, Vol. 17, No. 11-15). P., 1993)). The general structure of the spatial light modulator is shown in FIG. This spatial light modulator 61
Is a glass substrate 2, 2'with transparent conductive electrodes 3, 3 '
Thus, the photoconductive layer 4, the light reflection layer 5, and the light modulation layer 8 are sandwiched. The photoconductive layer 4 between the light reflection layers 5 is etched to form the light absorption layer 7. In the conventional spatial light modulation element 61, when the writing light 15 is input to the photoconductive layer 4, the voltage applied to the light modulation layer 8 changes according to the two-dimensional light intensity distribution, and the light modulation layer 8 is changed. Will switch.
As a result, the read light 22 is modulated, reflected by the light reflection layer 5, and then output. The light absorption layer 7 is for preventing the strong read light 22 from being input to the photoconductive layer 4 from between the light reflection layers 5.

FIG. 7 shows an image display device constructed by using this spatial light modulator. Readout light 2 from the light source 23
2 is incident from the light modulation layer 8 side of the spatial light modulation element 61,
After being modulated by the light modulation layer 8 and reflected by the reflection layer 5, the light passes through the light modulation layer 8 again and is output. Output light 24
Is visualized through the visualization means 25, and the projection lens 26
Is enlarged and projected on the screen 27. A liquid crystal material such as amorphous silicon (hereinafter abbreviated as a-SiC) for the photoconductive layer 4 of the spatial light modulator 61, and a nematic liquid crystal or ferroelectric liquid crystal (hereinafter abbreviated as FLC) for the light modulation layer 8. Is used. As the image source 13,
A self-luminous device or a non-luminous device such as a cathode ray tube (hereinafter abbreviated as CRT) or a thin film transistor drive type liquid crystal display (hereinafter abbreviated as TFT-LCD) is used, and these output images are used as writing light 15 by a writing lens 14. An image is input to the spatial light modulator 61 by forming an image on the photoconductive layer 4. Visualization means 2
A polarized beam splitter (hereinafter abbreviated as PBS) 5 is used, and a metal halide lamp, a xenon lamp, or the like is used as a light source.

[0004]

Contrast is an important parameter in evaluating an image. Factors that determine the contrast of the image display device using the conventional spatial light modulator as shown in FIG. 6 are the contrast of the image input source, the light modulation characteristics of the spatial light modulator, the degree of polarization separation of the visualization means, and the like. Was being considered. However, the contrast of the actual image remained low despite improvements in each property. In particular, when displaying an image in which a high-luminance region exists on a dark background, even the originally dark background becomes bright, and the proportion of the high-luminance region is large, and the higher the brightness, the lower the overall contrast. was there.

As a result of various studies, it has been clarified that this cause is multiple reflection of writing light inside the spatial light modulator 61. Consider a case where an arbitrary point of the CRT 13 emits light as shown in FIG. This point image is formed by the writing lens 14 on the photoconductive layer 4 of the spatial light modulator 61, but the input light 15 is the interface between the glass substrate 2 and the transparent conductive electrode 3, and the transparent conductive electrode 3 and the photoconductive layer 3. Part of it is reflected at the interface of layer 4. Most of the internally reflected light 16 reflected at a reflection angle substantially equal to the incident angle is the glass substrate 2
A part or all of the internally reflected light 17 that is output from the outside to the outside but is reflected at a reflection angle larger than the incident angle is reflected again at the interface between the glass substrate 2 and the outside air, and does not correspond to the input image. Since it is incident on the photoconductive layer 4 of No. 3, the periphery is slightly brightened and the image contrast is lowered.

The cause of the reflected light 17 is considered to be a scattering effect due to slight unevenness existing at the interface between the transparent conductive electrode 3 and the photoconductive layer 4. Further, in the case where extremely strong read light is applied to the spatial light modulator, by forming a light shielding layer on the transparent conductive electrode 3 between the light reflection layers 5, a part of the read light is emitted from the spatial light modulator. A structure for preventing penetration to the back surface is also conceivable, but in this case, it is considered that a reflected light component having a large reflection angle is generated due to the diffraction action of the light shielding layer having periodicity.

Even if an antireflection film is attached to the glass substrate 2, it seems that the rereflection of the internally reflected light at the interface between the glass substrate 2 and the outside air cannot be completely suppressed. Generally, when a light ray is incident from a medium having a large refractive index to a small medium, the reflectance at the interface increases as the incident angle increases, and the incident light ray exceeding the critical angle is totally reflected.
When a part 17 of the internally reflected light of the spatial light modulator 61 is incident on the glass substrate 2 at an incident angle close to the critical angle, even if the glass substrate 2 is provided with an antireflection film, a part of the reflected light or All are incident on the spatial light modulator again.

An object of the present invention is to solve the above problems and to provide a spatial light modulator capable of displaying a high-contrast image containing a part of a high-luminance region.

[0009]

In order to achieve the above object, the first structure of the spatial light modulator of the present invention comprises two glass substrates sandwiching a light modulating layer, a light reflecting layer and a photoconductive layer. ,
The transparent substrate fixed to the surface of the glass substrate on the side of the photoconductive layer, and at least one kind of transparent medium arranged between the glass substrate and the transparent plate. At least a part of the surface far from is a concave surface, and a light absorbing means is provided in a region of the transparent plate where the effective light beam does not pass, and an antireflection film is provided in a region where the effective light beam passes.

The second structure of the spatial light modulating element of the present invention comprises two glass substrates sandwiching a light modulating layer, a light reflecting layer and a photoconductive layer, and a glass substrate surface on the photoconductive layer side. A fixed light-transmitting plate and at least one kind of light-transmitting medium arranged between the glass substrate and the light-transmitting plate, and at least a partial region of a surface of the light-transmitting plate remote from the glass substrate is a concave surface. At least a part of the surface of the transparent plate close to the glass substrate is a convex surface, the light absorbing means is provided in a region of the transparent plate where the effective light flux does not pass, and the area where the effective light flux passes is antireflection. It is characterized by comprising a membrane.

In this case, at least one of the translucent media
The type is preferably liquid. Further, it is desirable that at least a part of the translucent medium is in contact with the heat dissipation means. Further, in the region where the effective light flux passes from the transparent plate to the glass substrate on the photoconductive layer side, it is desirable that the refractive index difference between two adjacent substances is 0.3 or less.

Further, a third structure of the spatial light modulator of the present invention is such that it is sandwiched between a light-transmitting plate having a photoconductive layer and a light-reflecting layer, a glass substrate, and the light-transmitting plate and the glass substrate. At least a part of the surface of the transparent plate far from the photoconductive layer is a concave surface, and the light absorbing means is provided in a region of the transparent plate where the effective light flux does not pass. It is characterized in that an antireflection film is provided in a region through which the light passes.

[0013]

The spatial light modulator of the present invention has a structure in which the glass substrate on the photoconductive layer side is provided with a light transmitting plate having a concave surface.
Even if the reflected light inside the spatial light modulator is totally reflected by the concave surface of the translucent plate, most of the reflected light is absorbed by the light absorbing means installed on the translucent plate and is returned to the photoconductive layer side. Decrease the ratio of. As a result, even if there is a high-luminance region in a part of the image, it is possible to suppress the deterioration of the contrast in the periphery.

Further, by using a liquid such as ethylene glycol, diethylene glycol, glycerin, or propylene glycol as the light-transmissive medium provided between the glass substrate and the light-transmissive plate, the temperature of the spatial light modulator exposed to strong readout light is increased. Suppress the rise. At this time, the translucent medium is in contact with the heat radiating means to further suppress the temperature rise of the spatial light modulator.

It is generally known that in order to reduce the reflectance at the interface between substances having different refractive indexes, it is sufficient to reduce the difference in refractive index. If the average refractive index of the two substances is 1.5, which is the refractive index of glass, optical resin, etc.,
If the difference in refractive index is 0.3 or less, the reflectance at the interface will be about 1
%, And the influence of the reflected light from the internal interface of the spatial light modulator on the contrast can be reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view of a spatial light modulator constructed in one embodiment of the present invention. In this spatial light modulator 1, a transparent conductive electrode 3, a photoconductive layer 4, and a light reflecting layer 5 are formed on a glass substrate 2, and the photoconductive layer 4 between the light reflecting layers 5 is formed.
Is etched to form a groove structure, and then the light absorption layer 7 is formed. A structure in which a part of the read light is prevented from penetrating to the back surface of the spatial light modulator 1 can be considered by forming a light shielding layer between the grooves between the light reflecting layers 5.

In the spatial light modulator 1 of this embodiment, the glass substrate 2'on which the glass substrate 2 and the transparent conductive electrode 3'are formed.
The light modulation layer 8 is sandwiched by the above, and a transparent plate 9 made of a plano-concave lens is bonded onto the glass substrate 2 with a transparent medium 10. The difference between the refractive index of the translucent medium 10 and the refractive index of the glass substrate 2 and the plano-concave lens 9 is 0.3.
The following medium is selected. Further, a light absorbing material 11 is provided in a portion of the plano-concave lens 9 where the effective light flux does not pass, and an antireflection film 12 is formed in a portion where the effective light flux passes.

As the transparent conductive electrode 3, ITO, Zn
O, SnO ₂ or the like can be used. As the photoconductive layer 4, CdS, CdTe, CdSe, ZnS, ZnS
e, GaAs, GaN, GaP, GaAlAs, InP
Such as compound semiconductors, amorphous semiconductors such as Se, SeTe, AsSe, Si, Ge, Si _1-x C _x , Si _1-x Ge _x , G
e _1-x C _x (0 <x <1) polycrystalline or amorphous semiconductor, and (1) phthalocyanine pigment (abbreviated as Pc), for example,
Metal-free Pc, XPc (X = Cu, Ni, Co, TiO,
Mg, Si (OH) _2, etc.), AlClPcCl, TiO
ClPcCl, InClPcCl, InClPc, In
BrPcBr and the like, (2) azo dyes such as monoazo dyes and disazo dyes, (3) penylene pigments such as penylene anhydride and penylene imide, (4) indigoid dyes, (5) quinacridone pigments, (6) anthraquinone , Polycyclic quinones such as pyrenequinones, (7) cyanine dyes, (8) xanthene dyes, (9) PVK / TNF
Such as charge transfer complex, (10) eutectic complex formed from pyrylium salt dye and polycarbonate resin, (11)
Organic semiconductors such as azurenium salt compounds can be used.

Amorphous Si, Ge, Si _1-x C _x ,
Si _1-x Ge _x , Ge _1-x C _x (hereinafter a-Si, a-G
e, a-Si _1-x C _x , a-Si _1-x Ge _x , a-Ge _1-x
Abbreviated as C _x . 2) is used for the photoconductive layer, hydrogen or a halogen element may be included, and oxygen or nitrogen may be included for decreasing the dielectric constant and increasing the resistivity. To control the resistivity, B and A which are p-type impurities
elements such as l and Ga, or P and A that are n-type impurities
Elements such as s and Sb may be added. By stacking the amorphous materials to which impurities are added in this manner, p / n, p / i, i
A junction such as / n, p / i / n or the like may be formed to form a depletion layer in the photoconductive layer to control the dielectric constant and dark resistance or the operating voltage polarity. In addition to such an amorphous material, a depletion layer may be formed in the photoconductive layer by forming a heterojunction by laminating two or more of the above materials. The film thickness of the photoconductive layer is preferably 0.1 to 10 μm. In this embodiment, 2 μm of a-Si having a p / i / n diode structure is used.
m to form a photoconductive layer 4. A as the light reflection layer 5
A metal having a high reflectance such as 1 or Ag may be used, and in the present embodiment, the light reflecting layer 5 was formed by depositing Cr and then Al to improve the strength in the case where the groove structure was formed. As the light modulation layer 8, a liquid crystal material such as ferroelectric liquid crystal, antiferroelectric liquid crystal, TN liquid crystal, STN liquid crystal can be used. In this embodiment, a ferroelectric liquid crystal capable of high speed response is used.

The image input to the spatial light modulator 1 is C
By combining the output image of the image input means 13 such as RT with the plano-concave lens 9, the spatial light modulator 1 is formed by the writing lens 14 which functions as one writing lens.
This is performed by forming an image on the photoconductive layer 4 of. As the image input means, a self-luminous device such as a CRT or T
A non-light emitting device such as FT-LCD can be used.

Part of the writing light 15 is reflected at the interface between the glass substrate 2 and the transparent conductive electrode 3 and at the interface between the transparent conductive electrode 3 and the photoconductive layer 4. The reflected light 16 reflected at each interface at a reflection angle substantially equal to the incident angle is reflected by the antireflection film 12.
By the effect of, the light is emitted to the outside without being reflected by the spatial light modulator 1 again. In the reflected light of each interface, the component 17 scattered by slight irregularities of the transparent conductive electrode, the photoconductive layer, etc. and having a large reflection angle is partially or wholly reflected on the concave surface of the plano-concave lens. These are not returned to the photoconductive layer 4 of the spatial light modulator 1 again by being absorbed by the peripheral light absorbing material 11.

Therefore, for the above reason, in the spatial light modulator 1, even when a high-luminance region exists in a part of the input image, the reduction of the peripheral contrast is suppressed, and the contrast of the projected image can be improved as compared with the conventional case. .

(Embodiment 2) Next, FIG. 2 is a sectional view of a spatial light modulator according to another embodiment of the present invention. In the spatial light modulation element 21 of the present embodiment, a resin having a concave recess formed in a portion through which an effective light flux passes is used as the light transmitting plate 9, and the glass substrate 2 and the glass substrate 2 via a spacer 18 having a window in the center. Glued. Further, in the present embodiment, the glass substrate 2 of the transparent plate 9 has a concave surface at least in the central portion of the surface of the transparent plate 9 which is far from the glass substrate 2.
The light absorbing material 11 is provided in the peripheral area of the translucent plate 9 where the effective light flux does not pass, and the antireflection film is provided in the substantially central area where the effective light flux passes. The structure is provided with 12.

Further, a light-transmitting liquid 19 as a light-transmitting medium is enclosed in a closed space formed by the glass substrate 2 and the light-transmitting plate 9. Other configurations are the same as in the first embodiment. still,
Also in this embodiment, the difference in refractive index between the transparent plate 9, the transparent liquid 19 and the glass substrate 2 is 0.3 or less. Also in the present embodiment, similarly to the first embodiment, even when a high-luminance region exists in a part of the input image, it is possible to suppress the deterioration of the peripheral contrast and improve the contrast of the projected image as compared with the conventional art. .

The translucent liquid 19 has a refractive index satisfying the above conditions and has a high transmittance for each wavelength component of the writing light, is inexpensive, is highly reliable, and can be used as a glass substrate or resin. On the other hand, a property such as low reactivity may be satisfied, but when the thermal conductivity and the thermal expansion coefficient are large and the kinematic viscosity coefficient is small, the temperature rise of the spatial light modulator can be suppressed. As the translucent liquid 19, ethylene glycol, diethylene glycol, glycerin, propylene glycol, an aqueous solution of these liquids, a mixed liquid of these liquids, or the like can be used.

Example 3 Next, FIG. 3 shows a spatial light modulator according to Example 3 of the present invention. FIG. 3 shows a spatial light modulator 3 in which a plano-concave lens is used for the translucent plate 9 and the glass substrate 2 and the translucent plate 9 are brought into close contact with each other by a spacer 18 having a window in the center.
2 is a sectional view of FIG. In this embodiment, the spacer 18 is made of a metal having a high thermal conductivity to enhance the heat dissipation effect. Also in the spatial light modulation element 1 configured in the present embodiment, even when a high-luminance region exists in a part of the input image, it is possible to suppress the deterioration of the peripheral contrast and improve the contrast of the projected image as compared with the conventional case. .

(Embodiment 4) Next, FIG. 4 shows a spatial light modulator according to Embodiment 4 of the present invention. FIG. 4 is a cross-sectional view of the spatial light modulation element 41 in which the heat radiation effect is further enhanced by installing the enlarged heat radiation surface 20 on the hollow metal spacer 18 'as the heat radiation means. Also in the spatial light modulator 1 configured in the present embodiment, even when a high-luminance region exists in a part of the input image, the reduction of the peripheral contrast is suppressed, and the contrast of the projected image is improved as compared with the conventional case. Furthermore, the temperature rise of the spatial light modulator 1 at the time of projection of 2000 lm was 5 ° C. or less with respect to room temperature, and there was practically no problem.

Example 5 Next, FIG. 5 shows a spatial light modulator in Example 5 of the present invention. FIG. 5 shows a transparent conductive electrode 3, a photoconductive layer 4, and a transparent conductive electrode 3 on the plane of a plano-concave lens which is a transparent plate 9.
This is a spatial light modulation element in which the light reflection layer 5 is formed, and other configurations are the same as those in the first embodiment. In the spatial light modulation element 1 of the present embodiment as well as in the other embodiments, even when a high brightness area exists in a part of the input image, the reduction of the peripheral contrast is suppressed, and the number of components is smaller than that of the conventional projection. The contrast of the image is improved. In addition, the present invention
Various modifications are possible based on the gist of the invention, and the invention is not limited to the above configuration.

[0030]

As described above, according to the present invention, it is possible to provide a spatial light modulator which is indispensable for constructing an image display device capable of displaying a high-contrast image including a part of a high-luminance region. You can

[Brief description of drawings]

FIG. 1 is a sectional view of a spatial light modulator according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a spatial light modulator according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a spatial light modulator according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a spatial light modulator according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a spatial light modulator according to a fifth embodiment of the present invention.

FIG. 6 is a sectional view of a conventional spatial light modulator.

FIG. 7 is a configuration diagram of an image display device configured using a conventional spatial light modulator.

FIG. 8 is a diagram showing internal reflection in a conventional spatial light modulator.

[Explanation of symbols]

 1 Spatial Light Modulator 2, 2'Glass Substrate 3, 3'Transparent Conductive Electrode 4 Photoconductive Layer 5 Light Reflecting Layer 7 Light Absorbing Layer 8 Light Modulating Layer 9 Light Transmitting Plate 10 Light Transmitting Medium 11 Light Absorbing Material 12 Reflection Preventing film 13 Image input means 14 Writing lens 15 Writing light 16 Internal reflected light component with reflection angle almost equal to incident angle 17 Internal reflected light component with large reflection angle

Claims (6)

[Claims] 1. A pair of glass substrates sandwiching a light modulation layer, a light reflection layer, and a photoconductive layer, a translucent plate fixed to the surface of the glass substrate on the photoconductive layer side, the glass substrate and the translucent substrate. An area including at least one kind of light-transmissive medium arranged between the light plates, at least a partial region of a surface of the light-transmissive plate remote from the glass substrate is a concave surface, and an effective light flux of the light-transmissive plate does not pass therethrough. 2. A spatial light modulator comprising a light absorbing means and an antireflection film in a region through which an effective light beam passes. 2. A pair of glass substrates sandwiching a light modulation layer, a light reflection layer, and a photoconductive layer, a translucent plate fixed to the surface of the glass substrate on the photoconductive layer side, the glass substrate and the translucent plate. A surface including at least one kind of light-transmissive medium disposed between the light plates, at least a partial region of a surface of the light-transmissive plate remote from the glass substrate is a concave surface, and a surface of the light-transmissive plate close to the glass substrate. At least a partial region of which is a convex surface, and a light absorbing means is provided in a region of the transparent plate through which an effective light beam does not pass, and an antireflection film is provided in a region through which the effective light beam passes. 3. The spatial light modulator according to claim 1, wherein at least one kind of the transparent medium is a liquid. 4. The spatial light modulator according to claim 1, wherein at least a part of the translucent medium is in contact with the heat dissipation means. 5. The difference in refractive index between two adjacent substances is 0.3 or less in a region through which an effective light flux passes from the transparent plate to the glass substrate on the photoconductive layer side. The spatial light modulator according to claim 1. 6. A light-transmitting plate having a photoconductive layer, a light-absorbing layer, and a light-reflecting layer formed thereon, a glass substrate, and a light-modulating layer sandwiched between the light-transmitting plate and the glass substrate. At least a part of the surface of the light-transmitting plate far from the photoconductive layer is a concave surface, and the light-absorbing means is provided in a region of the light-transmitting plate where the effective light beam does not pass, and the antireflection film is provided in a region where the effective light beam passes. A spatial light modulator characterized by being.