JPH0643481A - Spatial light modulator - Google Patents

Abstract

(57) [Summary] [Objective] To provide a high contrast spatial light modulator with a simple device. [Configuration] The spatial light modulation element 1 has a structure in which a transparent electrode 3, a light modulation layer 4, a conductive electrode 5, a photoconductive layer 6, and a transparent electrode 3 ′ are sandwiched between opposed substrates 2 and 7. An optical fiber plate having a small numerical aperture that forms a plurality of light propagation paths is used as the substrate 2 on the fourth side. As a result, the angle at which the read light 11 is incident on the light modulation layer 4 can be reduced, so that a high-contrast image can be read.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a projection display,
The present invention relates to a spatial light modulator used in a holography television, an optical arithmetic unit, or the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art High-definition televisions having large screens and high-density pixels have been developed and put into practical use in various systems. In particular, the development of projection-type displays using liquid crystal technology has been active in place of the conventional CRT method. In the cathode ray tube method, when the density of pixels is high, the brightness of the screen is lowered and the screen becomes dark. Moreover, it is difficult to increase the size of the cathode ray tube itself. Although a projection display device using a transmissive liquid crystal element of a transistor drive system is an effective method, the aperture ratio does not increase,
The disadvantage is that the device is expensive.

On the other hand, a liquid crystal light valve in which a light modulation layer made of liquid crystal is combined with a photoconductive layer is one in which an image is written from the photoconductive layer side and read light is modulated and reflected according to the spatial intensity distribution of the write light. Therefore, compared to the conventional projection type display, the degree of light amplification is large and a bright image can be obtained, and therefore, it is attracting attention.

The idea of a liquid crystal light valve was given by Hughes in the paper Applied Physics Letter 17 (1970) 51 (Appl. Phys. Lett. 17 (1970) 5
1) ZnS (photoconductive layer) + twisted nematic (T
N) The first is a liquid crystal structure. Liquid crystal light valve of CdS (photoconductive layer) + TN liquid crystal applied paper
Physics Letter 22 (1973) 90 (Appl.Phy
s. Lett. 22 (1973) 90). After that, single crystal silicon + TN liquid crystal was used in USP-4913531, JP-A-3-192332, and Journal of Applied Physics 5 (1985) 1356 (J.Appl.Phys.5 (1985) 1356).
Was announced in.

In recent years, it has become possible to display a moving image on a large screen of 100 inches or more by a liquid crystal light valve using a highly sensitive amorphous silicon as a photoconductive layer. For the first time, the use of a liquid crystal light valve made of amorphous silicon (a-Si) and TN liquid crystal for improving resolution was shown by US Pat.
Applied Optics 26 (1987) 241
(Appl. Opt. 26 (1987) 241) and USP-4538884.
In addition, a liquid crystal light valve using a photoconductive layer composed of a double layer of a-Si and CdTe is disclosed in USP-4799773 and SID International Symposium 199.
0 Digest of Technical Papers 1
7A. It is published in 2p327 (SID'90 17A.2 p327).

On the other hand, a liquid crystal light valve having a higher speed and a higher resolution has become possible by using a ferroelectric liquid crystal (FLC) which can respond at a high speed as a liquid crystal material. This liquid crystal light valve is also expected as the core of the next-generation parallel computing device and optical computing device as a spatial light modulator using the memory property and the binarization characteristic of FLC. A liquid crystal light valve with a diode structure a-Si + FLC is described in Applied Physics Letter 51 (1987) 123.
2 (Appl.Phys.Lett.51 (1987) 1232) is the first, but the idea is in the announcement of SPIE 754 (1987) 207. Other papers Applied Physics Letter 55 (198
9) 537 (Appl.Phys.Lett.55 (1989) 537) and USP-49.
There is a 41735 publication. The TV image writing and projection system was announced at the SID International Symposium 1991 Digest of Technical Papers 13.3 p254 (SID'91 13.3, p254).

On the other hand, a holographic television is attracting attention as a device that allows a user to view a three-dimensional stereoscopic moving image without glasses. In particular, a liquid crystal display element is expected as a rewritable hologram recording medium. For example, Hashimoto et al. Have constructed an electronic holography system using a high-density LCD as a phase-modulating spatial light modulator (SP.
Eye Proceeding Volume 1461
Practical holography V 1991 pp.
291-302 (SPIE Proc. Vol.1461, Practical
Holography V (1991) pp.291-302)). The resolution of current transistor drive type liquid crystal device is 12-25 lp /
mm, and it is desired to realize an element having 200 lp / mm in the future.

[0008]

The quality of the projected image is evaluated in terms of brightness, resolution, contrast and the like. An image on a projection display using a conventional liquid crystal light valve has a low contrast of about 50: 1. In order to improve the contrast, it is necessary to reduce the incident angle (angle from the normal line direction of the modulation layer) of the reading light to the liquid crystal which is the light modulation layer and make the light incident vertically. However, it is difficult to create a sufficiently bright and uniform parallel light source.
As shown in FIG. 1 of the publication, there is a problem that the configuration of the device is complicated because parallel reading light must be produced by an optical system using a lens.

The present invention has been made in view of the above problems of the conventional spatial light modulator, and an object of the present invention is to provide a spatial modulator having a good contrast and a simple apparatus structure.

[0010]

The spatial light modulator of the present invention is a spatial light modulator having a structure in which at least a photoconductive layer and a light modulating layer are sandwiched between first and second substrates facing each other. , The first substrate on which the light modulation layer is formed on one surface thereof is
It is provided with a plurality of light propagation paths for propagating the light irradiated to one surface opposite to the surface forming the light modulation layer to the light modulation layer.

[0011]

In the spatial light modulator of the present invention, the read light is incident on the light modulation layer through the first substrate having the light propagation path. The light that has entered the light propagation path enters the light modulation layer without cross-talking with the light that has entered the other light propagation paths. That is, only the light that has entered the light propagation path enters the corresponding light modulation layer. At this time, with respect to the thickness of the substrate in the light propagation direction,
When the aperture diameter of the light propagation path is sufficiently small, the angle of incidence of the readout light on the light modulation layer becomes extremely small, which is close to vertical incidence. This is because the read light having a large incident angle to the light propagation path is absorbed by the light absorption layer provided in the gap of the light propagation path and cannot reach the light modulation layer. Therefore,
In the spatial light modulation element of the present invention, the incident angle of the reading light that enters the light modulation layer can be made small, so that the contrast of the output image can be improved.

The same effect can be expected by using an optical fiber plate in which optical fibers having a small numerical aperture are bundled as an example of the first substrate. This is because when a fiber with a small numerical aperture is used, only the read light with a small incident angle to the optical fiber plate is propagated to the optical modulation layer, and as a result, the incident angle of the read light that enters the optical modulation layer becomes small, so the output image The contrast of can be improved.

[0013]

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

(Embodiment 1) FIG. 1 is a sectional view showing an embodiment of a spatial light modulator according to the present invention. This spatial light modulation element 1 includes an optical fiber plate 2 as a first substrate.
A transparent electrode 3, a light modulation layer 4, a conductive electrode 5, a photoconductive layer 6, and a transparent electrode 3'are sequentially laminated on top of this, and sandwiched by a substrate 7 as a second substrate. The optical fiber plate 2 has a structure in which a plurality of optical fibers 8 are bundled, and a light absorbing portion 9 is present in a gap between the optical fibers. The diameter of the core of the optical fiber 8 is, for example, about 2 to 50 μm, and may be determined according to the size of the conductive electrode 5.

As the transparent electrodes 3 and 3 ', for example, 0.0
A transparent electrode material such as ITO having a thickness of 5 to 0.5 μm was formed and formed by a sputtering method.

As the photoconductive layer 6, for example, hydrogenated amorphous silicon having a p / i / n diode structure (hereinafter a-S)
i: H) film is 1000 Å of p-type a-Si: H film added with 400 ppm of boron, i
A type a-Si: H film was 1.7 μm, and an n-type a-Si: H film containing 50 ppm of phosphorus was formed by plasma CVD so as to have a total thickness of 2000 μm and a thickness of about 2 μm.

It should be noted that the photoconductive layer 6 may be made of any material that has a large electric conductivity upon incidence of light, such as Cd.
S, CdTe, CdSe, ZnS, ZnSe, GaA
Compound semiconductors such as s, GaN, GaP, GaAlAs and InP, amorphous semiconductors such as Se and SeTeAsSe, S
i, Ge, Si _1-x C _x , Si _1-x Ge _x , Ge _1-x C _x (0 <x
<1) Polycrystalline or amorphous semiconductor, (1) Phthalocyanine pigment (hereinafter abbreviated as “Pc”), metal-free Pc, X
Pc (X = Cu, Ni, Co, TiO, Mg, Si (O
H) ₂ etc.), AlClPcCl, TiOClPcCl,
InClPcCl, InClPc, InBrPcBr, etc. (2) Azo dyes such as monoazo dyes and disazo dyes, (3) Penylene pigments such as penenylene anhydride and penenylene imide, (4) Indigoid dyes,
(5) Quinacridone pigment, (6) Polycyclic quinones such as anthraquinones and pyrenequinones, (7) Cyanine dyes, (8) Xanthene dyes, (9) Charge transfer complexes such as PVK / TNF, (10) Pyrylium salts A eutectic complex formed of a dye and a polycarbonate resin, an organic semiconductor such as (11) azurenium salt compound, or the like may be used. In addition, amorphous Si, Ge, Si _1-x C _x , Si _1-x Ge _x ,
Ge _1-x C _x (hereinafter a-Si, a-Ge, a-Si _1-x
C _x , a-Si _1-x Ge _x , a-Ge _1-x C _x ) is used for the photoconductive layer, it is also preferable to include hydrogen or a halogen element to reduce the dielectric constant. It is also preferred to include oxygen or nitrogen for the purpose and to increase the resistivity. In order to control the resistivity, an element such as B, Al, Ga, which is a p-type impurity, is added, or n is added.
It is also preferable to add elements such as P, As and Sb which are type impurities. In this way, the amorphous materials to which impurities are added are stacked to form p / n type, p / i type, i / n type, p / i / n
By forming a junction, such as a mold, and forming a depletion layer within the photoconductive layer, it is possible to control the dielectric constant and dark resistance or operating voltage polarity. Further, not only an amorphous material but also a depletion layer may be formed in the photoconductive layer by stacking two or more kinds of the above materials to form a heterojunction.

The conductive electrode 5 has a reflecting function, and aluminum is formed by, for example, electron beam evaporation.
23 μm square, 25 μm pitch, 1000 × 100 pixels
The thickness was 0 and the thickness was 500 to 1000Å. As the light modulation layer 4, a ferroelectric liquid crystal in which molecules were oriented by an orientation film so as to be parallel to the thickness direction of the device was formed. As the substrate 7, for example, a glass substrate was used.

Next, a method of driving the spatial light modulator 1 of this embodiment will be described. The spatial light modulator 1 is driven by applying an AC pulse voltage between the transparent electrodes 3 and 3 '.
When a negative pulse voltage is applied (reverse bias with respect to a-Si: H having a pin structure), a voltage drop occurs in the photoconductive layer 4. At this time, when the writing light 10 passes through the substrate 7 and is incident on the photoconductive layer 6, a photocurrent corresponding to the amount of incident light is generated and collected at the conductive electrode 5. As a result, the electric field strength applied to the light modulation layer 4 made of the ferroelectric liquid crystal in the portion where the conductive electrode 5 is formed increases. Ferroelectric liquid crystals have the property of reversing from the OFF state to the ON state when the applied electric field strength is above a certain threshold. Therefore, the ferroelectric liquid crystal changes to the ON state only when the sum of the incident light amounts satisfies the threshold value, and the OFF state is maintained when the incident light amount is less than the threshold value. Even after the negative pulse voltage is removed, the ferroelectric liquid crystal retains its state due to its memory function, and reads the light output during this period.

The output image is obtained by inputting the linearly polarized readout light 11 from the ferroelectric liquid crystal 4 side. In the spatial light modulator 1 of the present embodiment, the read light 11 is incident on the ferroelectric liquid crystal 4 after passing through the optical fiber plate 2. The incident light is transmitted to the ferroelectric liquid crystal 4 by the ferroelectric liquid crystal 4.
Then, it is modulated by the state of and is reflected by the conductive electrode 5. An output image is obtained by passing this reflected light through the crossed Nicols analyzer for the writing light 11. Initialization of the ferroelectric liquid crystal 4 is performed by applying a positive pulse voltage. As described above, the driving of the device consists of initialization when a positive pulse is applied and writing-reading when a negative pulse is applied, and high-speed operation of about 300 μsec per cycle is possible.

The optical fiber 8 forming the optical fiber plate 2 used in the spatial light modulator 1 of this embodiment has a small numerical aperture NA, for example, 0.1. It is guided to the ferroelectric liquid crystal 4. Therefore, the image can be read out with a simple configuration without deteriorating the contrast of the output image.

In the spatial light modulator 1 of this embodiment, for example, C
Optical writing was performed using RT, and the read image was projected on the screen. The contrast was about 400: 1.
It was confirmed that a clear image can be obtained.

(Embodiment 2) FIG. 2 is a sectional view of another embodiment of the spatial light modulator according to the present invention. The basic operation and configuration of the spatial light modulator 12 of this embodiment are the same as those of the spatial light modulator 1 of the first embodiment.

Optical propagation path 14 of substrate 13 used in this embodiment
Will be described with reference to FIG. FIG. 3 is a plan view of the substrate 13, and FIG. 4 is a sectional view of the substrate 13. The substrate 13 has a thickness of, for example, about 1 mm and a size of, for example, 50 × 50 mm ^2.
Is. As shown in FIG. 3, the substrate 13 has two-dimensionally arranged light propagation paths 14 each having a circular opening shape and covered with the light absorption portion 9.

The light propagation path 14 is, for example, a cylindrical glass having a diameter of 23 μm and a length of about 1 mm, and a side surface of the light absorption portion 9 is made of, for example, a pyropolymer obtained by sintering polyacrylonitrile (PAN) to a thickness of 2 μm. Formed. After the light propagation paths 14 were two-dimensionally bundled with a black silicon resin, the end face was optically polished to prepare the substrate 13.

As shown in FIG. 4, since the thickness of the substrate 13 is about 1000 μm with respect to the opening 23 μm of the optical propagation path 14, the incident angle of about 1.
Only light within 3 degrees. The read light having an incident angle larger than this angle is absorbed by the light absorbing portion 9 and cannot be emitted.

Therefore, in the spatial light modulation element 12 of the present invention in which the light modulation layer 4 is formed on the substrate 13, all the light incident on the light modulation layer 4 is close to parallel light within an incident angle of 1.3 degrees. Only light. Therefore, unlike the conventional case, it is not necessary to convert scattered light from a light source into parallel light by a lens optical system and enter the parallel light, and a high-contrast read image can be obtained with a simple configuration.

FIG. 5 is a block diagram of a projection type display constructed by using the spatial light modulator 12 of this embodiment. Optical writing was realized by focusing the image light from the high resolution CRT 15 on the photoconductive layer 6 of the spatial light modulator 12 using the gradient index rod lens array 16. The gradient index rod lens array 16 is a two-dimensional array of rod lenses having an aperture angle of 6 (deg), a diameter of 1 mm, and a length of 30 mm created by, for example, an ion exchange method. For example, it has black silicone resin. The rod lens has a parabolic refractive index distribution from the center to the periphery, and the light travels while meandering through it in a certain cycle. The lens length was set so that an erecting equal-magnification image could be formed with respect to the meandering period. To read the image, the light from the high-intensity metal halide lamp 17 was made to pass through the polarization beam splitter 18 and was incident on the spatial light modulator 12, and the reflected light was enlarged and focused on the screen 20 by the projection lens 19.

It was confirmed that this projection type display device had the following features. (1) An image enlarged to a size of 100 inches has an illuminance of 2500 lumens on the screen. (2) A high-resolution clear image of 1000 × 1000. (3) The contrast is 400: 1. (4) When a moving image was output, a clear high-luminance image was obtained with no afterimage due to the movement of the video rate.

The optical propagation path of the present invention is not limited to a circular cross section, and may be made of a material such as an optical fiber having another shape such as a quadrangle or glass.

[0031]

As is apparent from the above description,
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to configure a spatial light modulator that has a simple structure and can obtain a high-contrast output image, and realize a projection display device or the like that displays a clear large-screen image with high brightness and high contrast. It has advantages.

[Brief description of drawings]

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

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

FIG. 3 is a plan view of a substrate in the spatial light modulator of one embodiment according to the present invention.

FIG. 4 is a cross-sectional view of a substrate in a spatial light modulator according to an embodiment of the present invention.

FIG. 5 is a schematic view of a projection display device manufactured using the spatial light modulator of the present invention.

[Explanation of symbols]

 1 Spatial Light Modulator 2 Optical Fiber Plate 3, 3'Transparent Electrode 4 Light Modulation Layer 5 Conductive Electrode 6 Photoconductive Layer 7 Substrate 8 Optical Fiber 9 Light Absorber 10 Writing Light 11 Readout Light 12 Spatial Light Modulator 13 Substrate 14 Light Propagation Path 15 CRT 16 gradient index rod lens array 17 light source 18 polarization beam splitter 19 projection lens 20 screen

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukio Tanaka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inko Junko Asayama, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor, Kuni Ogawa, 1006, Kadoma, Kadoma, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A photoconductive layer having photoconductivity, a light modulation layer for light modulation, and first and second opposed substrates sandwiching at least both layers, the light modulation layer being one of the two. The space characterized in that the first substrate formed on the surface has a plurality of light propagation paths for propagating light irradiated to one surface opposite to the surface on which the light modulation layer is formed to the light modulation layer. Light modulator. 2. The spatial light modulator according to claim 1, wherein a light absorption layer is arranged around each light propagation path of the first substrate. 3. The spatial light modulator according to claim 1, wherein the first substrate is an optical fiber plate.