JPH09243986A - Spatial optical modulation device and display device formed by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate production and to make it possible to deal with reading out of white light by combining plural pieces of multiple layered thin-film reflection mirrors which reflect specific wavelength light, thereby constituting a light reflection layer. SOLUTION: This device has a structure obtd. by holding a translucent electrode 11, a photoconductive film 12, the light reflection layer 13, an optical modulation layer 14 and a translucent electrode 11 by two sheets of glass substrates 10. The light reflection layer 13 is constituted by combining the multiple layered thin-film reflection mirrors 30 having the reflection center wavelength of λ1 =450nm, the multiple layered thin-film reflection mirrors 31 having λ2 =550nm and the multiple layered thin-film reflection mirrors 32 having λ3 =650nm. The light reflection layer 13 is the multiple layered thin films which reflect light of the most visible wavelength region and is formed by combining >=3 pieces of the multiple layered reflection mirrors which reflect the specific wavelength light. Further, the reflection mirrors of short wavelengths among the specific wavelength light beams reflected from the plural multiple layered thin-film reflection mirrors are arranged successively from the reading out side.

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 for writing information by light and performing analog parallel processing of a projector, a moving image, and a still image, and a display device using the same.

[0002]

2. Description of the Related Art As a spatial light modulator for writing information by light, there is a conventional spatial light modulator, for example, Optics Letter, 1991, Vol. 16, pages 764-766,
I, E, E, Transaction on Electron Devices, 1989, Vol. 36, 2
Published on pages 959-2964. FIG. 3 shows a schematic sectional view of a conventional spatial light modulator. Light-transmissive electrode 11, photoconductive film 12 made of a-Si: H, light reflection layer 13 made of multi-layered thin film, light modulation layer 1 made of liquid crystal.
4. The transparent electrode 11 is sandwiched between two glass substrates 10.

In this device, a voltage is applied between the two translucent electrodes 11 so that the writing light 20 is incident on the photoconductive film,
The reflectance of the read light 21 incident from the opposite side of the device is changed according to the light intensity, and the output light 22 is obtained. That is, when the writing light 20 enters the photoconductive film 12, a photocurrent flows and the resistance value of the photoconductive film 12 decreases, so that the light modulation layer made of liquid crystal electrically connected in series with the photoconductive film 12. The voltage across 14 is modulated. Reading light 2
1 enters the light modulation layer 14, is reflected by the light reflection layer 13, and again passes through the light modulation layer 14 to become output light 22. At this time, the light modulation layer 14 modulates the phase, the polarization direction, or the amplitude of the read light according to the applied voltage.
2 is modulated according to the writing light 20.

[0004]

In the prior art, a multilayer thin film is used as a light reflecting layer in order to obtain a high reflectance and prevent deterioration of resolution. A monochromatic light source such as a laser beam is used as the reading light, and its emission wavelength is designed so that the peak wavelength of the reflectance in the light reflection layer matches the wavelength of the reading light. However, the multi-layered thin film has a very low reflectance for light other than a specific wavelength. That is, it does not have a good reflectance in the entire wavelength region of visible light. For this reason, when the read light is white light, part of the light is transmitted through the light reflection layer, so that the output light does not have sufficient intensity, and white output light cannot be obtained. Further, the light transmitted through the light reflection layer leaks into the photoconductive film to generate a photocurrent. The photocurrent generated in this way becomes a noise component for writing, and the SN of the spatial light modulator is increased.
It was a cause of lowering the ratio and the contrast ratio. Therefore, in the spatial light modulator according to the above-mentioned conventional technique, white light cannot be used as the reading light. Japanese Patent Application Laid-Open No. 05-173170 discloses an element using a metal material divided into pixels as a light reflection layer as a spatial light modulator compatible with the reading of white light. However, this device has a problem that it is not easy to manufacture because the structure is complicated.

It is an object of the present invention to obtain a spatial light modulator which is easy to manufacture and supports reading of white light.

[0006]

The above object is to have a light modulation layer, a light reflection layer, and a photoconductive film between at least a pair of translucent electrodes, and to adjust the write light incident on the photoconductive film. In the spatial light modulator that modulates the reflectance of the read light incident on the light modulation layer, the light reflection layer can be achieved by combining a plurality of multi-layered thin film reflecting mirrors that reflect light of a specific wavelength.

The light reflection layer is a multi-layered thin film that reflects light in most of the visible wavelength region, and by combining three or more multi-layered reflecting mirrors that reflect light of a specific wavelength, a plurality of layers can be provided. This is achieved by arranging the short-wavelength reflecting mirrors among the specific wavelengths reflected from the multi-layered thin-film reflecting mirror from the reading side.

Further, it is achieved by providing a filter or a light-shielding film between the photoconductive layer and the light source of the writing light, and absorbing or reflecting a part of light having a wavelength which is not reflected by the light reflecting layer.

[0009]

1 is a schematic view of a structure showing a cross section of a spatial light modulator according to the present invention. This device includes a translucent electrode 11, a photoconductive film 12, a light reflection layer 13, a light modulation layer 14,
It has a structure in which the translucent electrode 11 is sandwiched between two glass substrates 10. The light reflection layer 13 has a multi-layered thin film reflecting mirror 30 having a reflection center wavelength of λ ₁ = 450 nm, and λ ₂
= 550 nm, multi-layered thin film reflector 31, λ ₃ = 6
It is configured by combining a multi-layered thin film reflecting mirror 32 having a thickness of 50 nm. In the spatial light modulator according to the conventional technique, the spectral reflectance of the light reflecting layer covers only a portion near the monochromatic reading light as shown by the broken line in FIG. On the other hand, the light reflection layer of the spatial light modulator according to the present invention has a good reflectance in all visible light regions as shown by the solid line in FIG. Therefore, even when white light is used as the reading light, white output light having sufficient intensity can be obtained.

The multi-layered thin-film reflective mirror constituting the light reflection layer is composed of SiO ₂ , TiO ₂ , a-Si, ZnO ₂ , ZnS.
It can be obtained by periodically laminating at least two kinds of materials having different refractive indexes among e, ThF ₄ , As ₂ S _{3 and the} like. Here, in order to form a reflecting mirror having a reflection center wavelength of λ ₀ , the film thicknesses of two types of thin films having refractive indices of n ₁ and n ₂ are d ₁ = λ ₀ / 4n ₁ and d ₂ = λ _{As 0} / 4n ₂ , several layers or more may be periodically stacked.

The multi-layered thin-film reflective mirror thus obtained, by itself, had a wavelength region having a high reflectance, but was not always sufficient to cover the entire wavelength region of visible light. Therefore, when a plurality of multi-layered reflecting mirrors having central wavelengths separated by about 50 nm to 200 nm are used in combination, good reflection characteristics can be obtained for almost all wavelength regions of visible light. The combination of three or more becomes even better.

Generally, the thin film forming the multi-layered thin film reflecting mirror absorbs a part of visible light. The shorter the wavelength, the higher the absorption rate. Therefore, it is preferable that a plurality of multi-layered thin film reflective mirrors constituting the above-mentioned light reflecting mirror are arranged from the one having a short reflection center wavelength to the read light incident side, since light absorption in the light reflecting layer is minimized.

Further, even if the light reflecting layer having a good reflectance over the entire visible light range is formed, light in a low reflectance region mainly composed of ultraviolet light or infrared light is transmitted.
Part of the transmitted light is absorbed by the photoconductive layer and becomes a noise component of the writing light, which causes a reduction in the SN ratio and the contrast ratio of the spatial light modulator. A light component of such a wavelength can be suppressed by providing a filter between the photoconductive layer and the light source of the writing light and absorbing at least a part of the light of the wavelength which is not reflected by the light reflecting layer. Alternatively, it can be suppressed by providing a light-shielding film between the photoconductive layer and the light source of the writing light and reflecting at least a part of the light having a wavelength that is not reflected by the light reflecting layer. These lights are mainly ultraviolet light or infrared light, and the human eye has no sensitivity. Therefore, even if these light components are excluded, the output light intensity is not affected. The filter or the light shielding film may be provided on the optical path of the reading light outside the device, on the reading light incident side substrate, on the thin film forming the light reflecting layer, or between the light reflecting mirror and the photoconductive film.

As a photoconductive material, it is relatively easy to form a thin film having uniform characteristics over a relatively large area, and a-Si: H or a-Se having a large absorption coefficient in the visible light region.
Amorphous materials mainly composed of Si, CdS, CdSe,
CdTe, ZnS, ZnSe, ZnTe, CuIn
A polycrystalline material mainly composed of a photoconductive material such as S ₂ , CuInSe ₂ , CuGaS ₂ , CuGaSe ₂ is preferable. Such a photoconductive material absorbs light having a wavelength shorter than a specific wavelength, but does not absorb light having a long wavelength. The wavelength at this boundary is called an optical gap. A photoconductive material having an optical gap in the visible light region absorbs ultraviolet light to generate photocurrent, but it is not absorbed when infrared light is incident. Therefore, in this case, if the light component excluded by the filter or the light shielding film is applied only to the ultraviolet light, the effect of suppressing the noise component of the photocurrent due to the leakage of the read light into the photoconductive film can be obtained, and the device To improve the SN ratio and the contrast ratio.

As the light modulation layer, any liquid crystal material such as nematic liquid crystal or ferroelectric liquid crystal can be used.

[0016]

【Example】

First Embodiment FIG. 1 shows a schematic sectional view of a spatial light modulator according to the present invention. First, the transparent electrode 11 made of ITO is deposited on the glass substrate 10 to a thickness of 100 nm by a sputtering method. A-Si: H having P added thereto has a thickness of 10 nm,
A-Si: H without addition of 5 μm, a-S with addition of B
Photoconductive film 12 is obtained by sequentially stacking i: H of 10 nm. On top of this, SiO ₂ is 75.0 nm and TiO ₂ is 48.9 nm.
Multilayer laminated thin film mirror 3 having 10 layers alternately deposited by the sputtering method and having a reflection center wavelength of λ ₁ = 450 nm.
Get 0. Furthermore, SiO ₂ of 91.7 nm and T
Alternatingly 1 with io ₂ by 59.8 nm sputtering method
0 layers are deposited to obtain a multi-layered thin film reflective mirror 31 having a reflection center wavelength of λ ₁ = 550 nm. Add 1 SiO ₂ on top of this
Alternately, 10 layers of 08.3 nm and TiO ₂ were deposited by a 70.7 nm sputtering method, and the reflection center wavelength was λ ₁ =
A multi-layered thin film reflecting mirror 32 having a wavelength of 650 nm is obtained. The light reflecting layer 13 is formed by these three sets of multilayer laminated thin film reflecting mirrors. Then, the alignment film 16 is deposited on this. On the other hand, a transparent electrode 11 made of ITO is deposited on the other glass substrate 10 by a 100 nm sputtering method, and an alignment film 16 is further deposited. Both are bonded together via a spacer 17, and nematic liquid crystal is injected to obtain a spatial light modulator.

This device is provided with a transparent electrode 1 on the writing light incident side.
1 is used with a negative bias. When white light is used as the reading light, good light modulation is performed over the entire visible wavelength range. By combining this device with a white light source for reading or a beam splitter as shown in FIG. 5, for example, an optical system for obtaining output light can be formed. At this time, a filter 15 that absorbs ultraviolet light is incident on the reading light. When it is provided on the optical path, the ultraviolet light component leaking into the photoconductive film is suppressed, and the SN ratio and contrast ratio of the device are improved. The filter that absorbs the ultraviolet light may also be a light shielding plate that reflects the ultraviolet light.

Second Embodiment Another schematic sectional view of the spatial light modulator according to the present invention is shown in FIG. First, the transparent electrode 11 made of ITO is formed on the glass substrate 10 to a thickness of 100 nm by a sputtering method.
accumulate. On top of this, a photoconductive film 12 made of a-Se is formed.
It is deposited by the μm vapor deposition method. Add SiO ₂ on top of this
10 layers of 5.0 nm and TiO ₂ were alternately deposited by a 48.9 nm sputtering method, and the reflection center wavelength was λ ₁ = 45.
A 0 nm multilayer laminated thin film mirror 30 is obtained. Si on this
By alternately depositing 10 layers of O ₂ of 108.3 nm and TiO ₂ of 70.7 nm by a sputtering method and setting the reflection center wavelength to λ
A multi-layered thin film reflecting mirror 31 with ₁ = 650 nm is obtained.
A light reflecting layer 13 is formed by the two sets of multilayer laminated thin film reflecting mirrors, and an alignment film 16 is deposited thereon. On the other hand, the transparent electrode 11 made of ITO is formed on the other glass substrate 10.
Is deposited to a thickness of 100 nm by the sputtering method, and the alignment film 16 is further deposited. Then, a filter 15 that absorbs ultraviolet rays is deposited on the reflecting surface. The two are bonded together via a spacer 17, ferroelectric liquid crystal is injected to provide the light modulation layer 14, and a spatial light modulator is obtained.

This device is provided with a transparent electrode 1 on the writing light incident side.
1 is used with a positive bias when writing. This device is inferior to the first embodiment in reflection characteristics over the entire visible light range, but since the light reflection layer is relatively thin, the voltage drop in this portion is small. Therefore, it is suitable for driving the light modulation layer. Further, in the present embodiment, the filter for absorbing ultraviolet light may be a light shielding film for reflecting ultraviolet light. However, the filter is preferable to the light-shielding film because it may generate heat.

Third Embodiment FIG. 6 shows a projector system as an example of a display device using the spatial light modulator according to the above embodiments of the present invention. The image signal emitted from the cathode ray tube is input from the photoconductive layer side of the spatial light modulator of the present invention through the lens. Then, the reflectance of the surface on the opposite side of the spatial light modulator is modulated according to the image signal. By combining this device with a beam splitter prism, white light can be read out in a spatial light modulator that writes information by light and performs analog parallel processing of projectors, moving images, and still images. The noise component resulting from the leakage into the photoconductive film is suppressed, and the SN ratio and the contrast ratio of the spatial light modulator are increased.

[0021]

Industrial Applicability The present invention enables white light reading in a spatial light modulator for writing information by light and performing analog parallel processing of a projector, a moving image, and a still image, and leaks the read light to the photoconductive film. The noise component caused by the noise is suppressed, and the SN ratio and the contrast ratio of the spatial light modulator are increased.

[Brief description of drawings]

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

FIG. 2 is a spectral reflectance of a light reflecting layer.

FIG. 3 is a schematic sectional view of a spatial light modulator according to the prior art.

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

FIG. 5 is a diagram showing an example of an optical system for obtaining output light of a spatial light modulator combined with a white light source.

FIG. 6 is a diagram showing an example of a display device using the spatial light modulator of the present invention.

[Explanation of symbols]

 11 translucent electrode 12 photoconductive film 13 light reflection layer 14 light modulation layer 15 filter 20 writing light 21 reading light 30, 31 multi-layered thin film reflective mirror

Claims (8)

[Claims] 1. A light modulation layer, a light reflection layer, and a photoconductive film are provided between at least a pair of translucent electrodes, and the light modulation layer, the light reflection layer, and the photoconductive film are incident on the light modulation layer in response to write light incident on the photoconductive film. In a spatial light modulator that modulates the reflectance for read light,
A spatial light modulator comprising a plurality of multi-layered thin-film reflective mirrors in which the light reflection layer reflects light of a specific wavelength. 2. The spatial light modulator according to claim 1, wherein the light reflection layer is a multilayer thin film that reflects light in at least most visible light wavelength regions. 3. The spatial light modulator according to claim 1, wherein the light reflecting layer is formed by combining three or more multi-layered thin film reflecting mirrors that reflect light of a specific wavelength. 4. The plurality of multilayer thin film reflecting mirrors constituting the light reflecting layer are characterized in that reflecting mirrors having a short specific wavelength to be reflected are arranged in order from the reading light side. The spatial light modulator according to claim 1 or 3. 5. The photoconductive layer comprises a filter between light sources of writing light, and reflects at least a part of light having a wavelength which is not reflected by the light reflecting layer. The spatial light modulator described in any one of 1. 6. The photoconductive layer comprises a light-shielding film between light sources for writing light, and absorbs at least a part of light having a wavelength which is not reflected by the light reflecting layer. 4. The spatial light modulator according to any one of 4 above. 7. The spatial light modulator according to claim 5, wherein the light having a wavelength that does not reflect is ultraviolet light. 8. A display device using the spatial light modulator according to any one of claims 1 to 7.