JPH0651341A - Spatial optical modulation element - Google Patents

Abstract

PURPOSE:To provide the spatial optical modulation element having high image quality by providing a light absorption layer consisting of diamond-like carbon between a dielectric mirror and a photoconductive layer. CONSTITUTION:The light absorption layer 31, the dielectric mirror 32, a high- polymer liquid crystal composite film 33, a transparent electrode 34 consisting of ITO and a glass plate 35 are successively superposed on one surface of a BSO wafer 30. A transparent electrode 36 consisting of ITO is brought into tight contact with the other surface of the BSO wafer 30. The diamond-like carbon film constituting the light absorption layer 31 is capable of sharpening the electric field distribution impressed to the optical modulation layer 33 by its high specific resistance and is capable of enhancing the quality of the read- out image by enhancing the optical isolation between the photoconductive layer 30 and the optical modulation layer 33 and sufficiently preventing the incidence of reading-out light on the photoconductive layer 30. Further, the above- mentioned film facilitates and assures the adhesion to the optical modulation layer 33 for its high heat resistance and surface smoothness. The bright image is, therefore, displayed and this element is utilizable for the high-resolution image display, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing type spatial light modulator, and more particularly, it uses writing light to input two-dimensional information such as an image, and uses reading light to output the two-dimensional information. The present invention relates to an optical writing type spatial light modulator.

[0002]

2. Description of the Related Art Various spatial light modulators have been developed for the purpose of two-dimensional information processing or display.

FIG. 5 shows a structure of a spatial light modulator of a type having a high response speed and a high utilization efficiency of read light (Takizawa et al., Autumn Electronic Information Society of 1989, C-338, or JP-A-2-93519). etc). As shown in the figure, this element has a laminated structure of an ITO transparent electrode 1, a photoconductive layer 2, a reflective layer 3, a light modulation layer 4 and an ITO transparent electrode 5,
The ITO transparent electrode 5 is covered with glass 6. In such a structure, the light modulating layer 4 is made of polymer dispersed liquid crystal, the light reflecting layer 3 is made of a dielectric mirror, and the light modulating layer 4 is made of B.
An i ₁₂ SiO ₂₀ (hereinafter abbreviated as BSO) single crystal wafer is used.

First, when the writing light 7 is not applied to the photoconductive layer 2, the impedance of the photoconductive layer 2 is sufficiently high and almost no electric field is applied to the liquid crystal of the light modulation layer 4. Therefore, the liquid crystal molecules are randomly aligned,
The read light 8 is scattered due to the difference in refractive index between the polymer and the liquid crystal in the light modulation layer 4. On the other hand, when the photoconductive layer 2 is irradiated with the writing light 7, the impedance thereof is lowered by the photoconductive effect of BSO, and the electric field is applied to the light modulation layer 4. As a result, the liquid crystal molecules are oriented in the direction of the electric field, but the ordinary light refractive index of the liquid crystal and the refractive index of the polymer match each other, and the read light 8 is reflected by the reflective layer 3 without being scattered. . Therefore, when an image is input as the writing light 7, the reading light 8 is reflected corresponding to the in-plane intensity distribution of this image, and an output image can be obtained. In this element,
Since BSO is used as the photoconductive layer 2 and polymer dispersed liquid crystal is used as the light modulation layer 4, the response speed is high and moving images can be displayed at the TV rate. Further, since no polarizing plate is used in the read output portion, a high light utilization rate and a bright image can be obtained.

FIG. 6 is a view showing the structure of a liquid crystal light valve (LCLV) which is another spatial light modulator (J. Grinberg, Opt. Eng., Vol. 1).
4,217 (1975)). As shown, in this device, CdS
The ITO transparent electrode 13 is formed on one surface of the photoconductive layer 12 made of
And the surface of the ITO transparent electrode 13 is covered with a transparent plate 14. On the other hand, on the other side surface of the photoconductive layer 12, a light absorption layer 15 made of CdTe, a reflection layer 16 made of a dielectric mirror, a light modulation layer 17, and an ITO transparent electrode 18 are sequentially stacked. Further, the ITO transparent electrode 18 is covered with glass 19. The light modulation layer 17 is a liquid crystal alignment layer 17 facing the crystal 17a operating in the hybrid electric field mode with the crystal 17a interposed therebetween.
b, 17c.

The operation of this element will be described below. First,
Writing light 20 having two-dimensional image information is made incident on the photoconductive layer 12 side. As a result, the impedance of the photoconductive layer 12 decreases corresponding to the light intensity distribution, and accordingly the liquid crystal 1
The effective electric field applied to 7a changes. When the read light 21 is incident on the liquid crystal 17a from the ITO transparent electrode 18 side,
The read light 21 is modulated according to the distribution of the electric field applied to the liquid crystal 17a. The modulated read light 21 is reflected by the reflective layer 16
Then, the reading light 21 is reflected by and is emitted again as an output image from the input side.

[0007]

The reflective layer 3 shown in FIG.
Usually, a dielectric multilayer film mirror is used. The reason is that it is necessary to sharply apply the electric field distribution formed in the surface of the photoconductive layer 2 to the light modulation layer 4 in accordance with the intensity of the writing light. This is because a low resistance material such as a metal mirror cannot be used.

Dielectric multilayer mirrors have two different refractive indexes.
A plurality of types of dielectrics are alternately laminated, and the multiple interference of light in the film is used to increase the reflectance with respect to incident light in a specific wavelength range. Refractive index n ₁ , n ₂ (n ₁ >
n ₂ ), a two-layer film in which each dielectric layer is alternately stacked is repeated p
The maximum reflectance R of the laminated multilayer film is given by the following equation.

[0009]

[Equation 1]

Where n ₀ is the refractive index of the external material, and n _s
Is the refractive index of the substrate.

For example, TiO ₂ and Si are placed on a quartz glass plate.
When O ₂ and 8 are alternately laminated (n ₁ = 2.35, n
₂ = 1.46) and R = 0.997. From equation (1), it can be seen that it is impossible to set R = 1. Further, in the element of FIG. 5, polymer dispersed liquid crystal is used as the light modulation layer 4, but since this liquid crystal uses light scattering for modulation of the read light, the read light incident on the OFF-state region is The light is scattered by the light modulation layer 4 and obliquely enters the dielectric multilayer mirror. In this case, since the reflection condition of the mirror is designed for vertically incident light, the mirror transmittance of such obliquely incident light becomes high.

As described above, in this device structure, since a part of the read light reaches the photoconductive layer, the resistivity of the photoconductive layer is lowered and the electric field distribution formed on the photoconductive layer 2 by the write light is erased. Alternatively, it is attenuated and the electric field distribution applied to the light modulation layer 4 becomes dull, and as a result, the quality of the read image deteriorates. In order to solve this problem, the addition of a light absorption layer is being studied. This is because a light absorption layer having a high light absorption coefficient is inserted between the dielectric mirror layer and the photoconductive layer so that the read light passing through the dielectric mirror layer is incident on the photoconductive layer. The idea is to block light. The properties required for the light absorption layer are high light absorption coefficient, high specific resistance, high heat resistance, surface smoothness, and adhesion to the photoconductive layer. Among them, the heat resistance is due to heating during the coating process of the dielectric multilayer mirror on the light absorption layer, and is usually 20
Heat resistance to 0 ° C to 300 ° C is required.

In the conventional example shown in FIG. 6, CdTe is used as such a light absorbing layer.
Since it is difficult to control the composition, it is difficult to obtain a thin film having a high specific resistance. Also, since it has a photoconductive effect, there is a problem that the resistance is further lowered when the intensity of read light is large.

As a material having a high resistance ratio and heat resistance, a heat resistant polymer film such as polyimide can be used. A film having a low transmittance can be obtained by dispersing a pigment or a dye in polyimide, but it is difficult to obtain a film that completely satisfies the specifications of the spatial light modulator.

Heat resistant pigments (carbon and inorganic pigments)
In order to disperse while suppressing secondary aggregation and obtain a film having a smooth surface on the order of submicron, it is necessary to considerably increase the ratio of resin components, and it is difficult to sufficiently increase the absorption coefficient of the film. Therefore, in order to suppress the transmittance, the thickness of the light absorption layer must be increased to 3 to 4 μm. As a result, when the electric field distribution formed in the photoconductive layer is applied to the modulation layer, the sag in the in-plane direction becomes large, and the resolution of the read image quality deteriorates.

On the other hand, in the case of dyes, there are few materials having heat resistance of 150 ° C. or higher, and the light absorption coefficient is relatively low.
It is not possible to obtain a light absorption layer with satisfactory performance.

Therefore, the present invention solves the above problems,
An object of the present invention is to obtain a high-quality spatial light modulator by forming a high-performance light absorbing layer.

[0018]

In order to solve the above-mentioned problems, the spatial light modulator according to the present invention has (a) a photoconductive layer formed of a photoconductive material, and (b) an incident light depending on an applied voltage. A light modulation layer for changing the state of the light, and (c) a dielectric mirror provided between the photoconductive layer and the light modulation layer,
(D) A light absorption layer made of diamond-like carbon provided between the dielectric mirror and the photoconductive layer is provided.

[0019]

According to the above spatial light modulator, the light absorption layer made of diamond-like carbon is provided between the dielectric mirror and the photoconductive layer. Diamond-like carbon has a high specific resistance required for the light absorption layer of the spatial light modulator. Also, the light absorption coefficient is extremely high over a predetermined wavelength range. Further, the diamond-like carbon layer can have high heat resistance and high surface smoothness. Therefore, the light absorption layer formed of diamond-like carbon can have a sharp electric field distribution applied to the light modulation layer because of its high specific resistance. Further, it is possible to enhance the optical isolation between the photoconductive layer and the light modulation layer, sufficiently prevent the read light from entering the photoconductive layer, and enhance the quality of the read image. Furthermore, because of its high heat resistance and surface smoothness, it becomes easy to adhere to the light modulation layer.

In this case, the photoconductive layer 9 is formed of Bi ₁₂ SiO ₂₀ single crystal or Bi ₁₂ GeO ₂₀ single crystal which is a photoconductive material, and the photoconductive layer and the light absorbing layer are formed of SiO ₂ or the like. Adhesion between the photoconductive layer and the light absorbing layer can be enhanced if they are attached via the buffer layer.

[0021]

EXAMPLE FIG. 1 is a diagram showing the configuration of a spatial light modulator according to the first example. A light absorption layer 31, a dielectric mirror 32, a polymer liquid crystal composite film 33, an ITO transparent electrode 34, and a glass plate 35 are sequentially stacked on one surface of the BSO wafer 30. Further, an ITO transparent electrode 36 is in close contact with the other surface of the BSO wafer 30.

The spatial light modulator of FIG. 1 was manufactured as follows. First, 35 × 35 × 0.
On one side of the 5 mm ³ BSO (100) wafer 30,
An ITO transparent electrode 36 having a composition in which 5% Sn is added to In ₂ O ₃ is coated, and on the other surface, a thin film light absorption layer 31 made of diamond-like carbon and having a thickness of 1.1 μm, and TiO ₂ and SiO _{2. The} dielectric mirror 32 composed of _two multilayer films was sequentially formed. Diamond-like carbon to be the light absorption layer 31 was coated by a plasma CVD method using methane gas as a raw material. The obtained light absorption layer 31 had a transmittance of 0.02% for light of 450 nm. The multilayer film such as TiO ₂ that constitutes the dielectric mirror 32 was coated by the electron beam evaporation method. The obtained dielectric mirror 32 had a reflectance of 97% or more with respect to light of 410 to 490 nm.

Next, 40 × 40 mm with both sides optically polished
ITO transparent electrode 3 on one surface of glass plate (BK7) 35 of ²
4 was formed. ITO transparent electrode 3 on this glass plate 35
4 was coated with a polymer liquid crystal composite film 33 having a film thickness of 20 μm. The polymer liquid crystal composite film 33 is formed by mixing liquid crystal and polymer matrix. Specifically, using a nematic liquid crystal as the liquid crystal and an acrylic polymer as the polymer matrix,
These were mixed at a compounding ratio of 1: 1. Domains were formed by each in the coated composite membrane. In this case, the ordinary refractive index of the nematic liquid crystal and the refractive index of the acrylic polymer were adjusted to match.

Finally, the dielectric mirror 32 and the polymer liquid crystal composite film 33 were pressure-bonded to each other, and the BSO wafer 30 and the glass plate 35 were integrated. As a result, a spatial light modulator as shown in FIG. 1 was obtained.

FIG. 2 is a diagram showing for reference the wavelength dependence of the transmittance of the diamond-like carbon film used as the light absorption layer 31 in the spatial light modulator of FIG. A diamond-like carbon film having a film thickness of 1.3 μm coated by the plasma CVD method was used for the measurement.
As shown in the figure, this diamond-like carbon film has a low transmittance in the wavelength region of 400 to 550 nm, and when a photoconductive material having a photoconductive effect in this wavelength region is used for the photoconductive layer of the spatial light modulation element, the It can be seen that it is suitable as a material for the absorption layer. Also, the specific resistance is 2.2 × 10 ⁸ Ω
cm, and the surface smoothness is very good. That is, the light absorption layer formed of the diamond-like carbon film has a high light absorption coefficient, high specific resistance, high heat resistance, and surface smoothness.

The spatial light modulation element formed as described above was set in an optical system as shown in FIG. 3 and its operation characteristics were evaluated. In this optical system, the writing light emitted from the writing light source 50 is collimated by the convex lens 51 and then irradiated on the liquid crystal panel 52, and the input image displayed on the liquid crystal panel 52 is measured via the convex lens 53. An image is formed on the spatial light modulation element 54 for use. On the other hand, the display light source 6
The readout light emitted from 0 passes through the convex lens 61, the optical path is deflected by the reflecting mirror 62, and the spatial light modulator 54 is irradiated with the light through the lens 63. The output light of the spatial light modulator 54 passes through the lens 63 again, then passes through the lens 64, and is enlarged and projected as a blue image on the screen 65.

A xenon lamp was used as the writing light source 50, and the writing light was short-wavelength light having a wavelength of 400 to 550 nm, which BSO has high sensitivity. Xenon lamp light that passed through a blue dichroic filter having a transmission band of 400 to 500 nm was used as the reading light. The output light was magnified and projected on the screen 65 with a diagonal length of 2 m. At this time, the spatial light modulator 54 has 20
A voltage of V _rms , 100 Hz was applied. The liquid crystal panel 52 has a diagonal length of 76 mm and has 90,000 pixels.

A video image was input to the liquid crystal panel 52 and projected on a screen 65 to measure the characteristics of the spatial light modulator 54. BSO does not have photoconductive sensitivity and spatial light modulator 5
Compared to the image displayed in red using a display light source that emits red light that does not require a light absorption layer in 4, the projected blue image was slightly inferior in both resolution and contrast. It was possible to obtain a considerably clearer image than the projected image of the element using the light absorbing layer such as.

FIG. 4 is a diagram showing the structure of the spatial light modulator according to the second embodiment. This spatial light modulator is a BS
The buffer layer 131 is provided between the O wafer 30 and the light absorption layer 31.
Is provided. In addition, the same parts as those in the first embodiment of FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The spatial light modulator of FIG. 4 was manufactured as follows. First, ITO is formed on one surface of the BSO wafer 30.
The transparent electrode 36 was coated. Next, on the other surface of the BSO wafer 30, a buffer layer 131 made of SiO ₂ and having a thickness of 0.3 μm and a thin light absorption layer 31 made of diamond-like carbon and having a thickness of 1.1 μm were sequentially formed. Then, the dielectric mirror 32 made of a multilayer film was formed. The formation of the light absorption layer 31 and the dielectric mirror 32 was the same as in the first embodiment. The formation of the buffer layer 131 is
Similar to the dielectric mirror 32, the coating was performed by the electron beam method. Next, an ITO transparent electrode 34 was formed on one surface of the glass plate 35, and a polymer liquid crystal composite film 33 having a thickness of 20 μm was further coated thereon. Similar to the first embodiment, the polymer liquid crystal composite film 33 is formed by mixing nematic liquid crystal and a resin matrix having the same refractive index as that of nematic liquid crystal. Finally, the dielectric mirror 32 and the polymer liquid crystal composite film 33 are pressure-bonded to each other and bonded to each other.
0, the glass plate 35, etc. were integrated. As a result, a spatial light modulator as shown in FIG. 4 was obtained.

Hereinafter, the buffer layer 131 is formed on the BSO wafer 3
The reason for interposing between 0 and the light absorption layer 31 will be briefly described.

The diamond-like carbon film used as the light absorption layer 31 has a transmittance of 0.02% at 450 nm.
And the absorption coefficient is 65,500 cm ^-1 , and the film thickness is 1.0
It can be seen that the performance with a transmittance of 0.1% or less is obtained at 5 μm. Further, as described above, the diamond-like carbon film has high specific resistance, high heat resistance and surface smoothness. However, the coefficient of linear expansion of diamond-like carbon is 1 to 3 × 10 ^-6 ° C ^-1, which is greatly different from the linear expansion coefficient of BSO of 16 × 10 ^-6 ° C ^-1 , for example. Therefore, BS
Even if a wafer such as O or BGO is directly coated with diamond-like carbon, there is a problem that it is easily peeled off and has poor adhesion. Therefore, in the second embodiment, an intermediate linear expansion coefficient (5 to 10 × 10 5) between them is provided.
^The SiO ₂ buffer layer 131 having a temperature of ⁻⁶ ° C. ⁻¹ ) is inserted to prevent the diamond-like carbon light absorption layer 31 from peeling off.

The spatial light modulation element formed as described above was set in an optical system as shown in FIG. 3 and its operation characteristics were evaluated.

A video image was input to the liquid crystal panel 52 and projected on a screen 65 to measure the characteristics of the spatial light modulator. Similar to the spatial light modulator of the first embodiment, the projected blue image was slightly inferior in resolution and contrast as compared with the image displayed in red, but a conventional light absorbing layer such as a polyimide film was used. Compared to the projected image of the device, a clear image could be obtained.

The present invention is not limited to the above embodiment. For example, diamond-like carbon is 500n
Since it has a high light-shielding property for short-wavelength light of m or less, various materials having high sensitivity in this wavelength region can be used as the photoconductive material. As such a photoconductive material, BS
In addition to O, Bi ₁₂ GeO ₂₀ (BGO), a-SiC, or the like can be used. Further, as a buffer layer, SiO ₂
In addition to the above, various materials having a linear expansion coefficient intermediate between those of the photoconductive layer and the light absorbing layer and having good adhesiveness to these can be used.

[0036]

As described above, in the spatial light modulator of the present invention, the light absorption layer made of diamond-like carbon is provided between the dielectric mirror and the photoconductive layer. Therefore, the electric field distribution applied to the light modulation layer can be made sharp by the high specific resistance of diamond-like carbon. Further, it is possible to enhance the optical isolation between the photoconductive layer and the light modulation layer, sufficiently prevent the read light from entering the photoconductive layer, and enhance the quality of the read image. Further, because of the high heat resistance and surface smoothness of diamond-like carbon, adhesion with the light modulation layer becomes easy and reliable. Therefore, the spatial light modulation element of the present invention can display a clear image, and can be effectively used for applications such as a high-resolution image display.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a spatial light modulation element according to a first example.

FIG. 2 is a diagram showing an example of transmittance wavelength dependence of a diamond-like carbon film used for forming the spatial light modulator of FIG.

FIG. 3 is a schematic diagram showing an optical system for evaluating the characteristics of a spatial light modulator.

FIG. 4 is a cross-sectional view showing the configuration of the spatial light modulator of the second embodiment.

FIG. 5 is a configuration diagram of an example of a conventional spatial light modulator.

FIG. 6 is a configuration diagram of another example of a conventional spatial light modulator.

[Explanation of symbols]

30 ... Photoconductive layer, 31 ... Light absorbing layer, 32 ... Dielectric mirror, 33 ... Light modulating layer, 131 ... Buffer layer. Attorney Attorney Yoshiki Hasegawa

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kikuchi 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the broadcasting technology research institute of Japan Broadcasting Corporation (72) Kouji Tada 1-chome, Shimaya 1-chome, Osaka, Osaka No. 3 Sumitomo Electric Industries, Ltd. Osaka Works

Claims (3)

[Claims] 1. A photoconductive layer formed of a photoconductive material, a light modulation layer that changes a state of incident light according to an applied voltage, and a photoconductive layer provided between the photoconductive layer and the light modulation layer. A spatial light modulator comprising: a dielectric mirror; and a light absorbing layer made of diamond-like carbon provided between the dielectric mirror and the photoconductive layer. 2. The photoconductive layer is made of Bi ₁₂ which is a photoconductive material.
_2. The spatial light modulator according to claim 1, wherein the spatial light modulator is made of SiO ₂₀ single crystal, and the photoconductive layer and the light absorbing layer are attached via a buffer layer made of SiO ₂ . 3. The photoconductive layer comprises a photoconductive material of Bi _12
2. The spatial light modulator according to claim 1, wherein the spatial light modulator is made of GeO ₂₀ single crystal, and the photoconductive layer and the light absorbing layer are attached via a buffer layer made of SiO ₂ .