JPH0736055A - Spatial optical modulator - Google Patents

Abstract

PURPOSE:To provide a spatial optical modulator capable of conducting computation between images and feedback with a simple optical system. CONSTITUTION:Transparent electrode layers 12a, 12b are formed on the surface of a pair of substrates 11a, 11b for clamping a liquid crystal and photoconductive layers are formed on the respective transparent electrodes. Further, the surfaces of both substrates 11a, 11b are provided thereon with oriented film layers 13a, 13b in such a manner that the incident directions on both substrates in the assembled state align to each other. A sealing material prepd. by mixing and dispersing spacer materials into an outer peripheral sealing material is applied on a pair of the substrates 11a, 11b and thereafter, two sheets of the substrates 11a, 11b are adhered to form a spacing to clamp the liquid crystal. A liquid crystal compsn. 14 is clamped in this spacing. As a result, systems, such as optical information processing system and optical neural net, are more easily and compactly than in the case of use of the conventional spatial optical modulator.

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 applied to optical information processing, optical computing and optical neural networks.

[0002]

2. Description of the Related Art Conventionally, a spatial light modulator using liquid crystal has been used as an element for intensity-modulating and outputting input image information in real time. In particular,
The spatial light modulator using ferroelectric liquid crystal as the modulation layer shown in −68967 and the like has characteristics such as high contrast, high resolution, and high speed response, and is used as an optical information processing device.

[0003]

However, in a conventional spatial light modulator using a liquid crystal, since the writing surface is limited to one direction, feedback is applied when it is applied to, for example, an optical neural network. However, there is a drawback that a complicated optical system is required for the operation and the optical axis adjustment is very difficult.

Further, when performing calculation between images, it is necessary to superimpose the images using a half mirror or the like on the writing side or to project from an oblique direction. All of these methods are difficult to adjust the optical axis and form an image. Further, in the former case, the maximum light amount is less than 1/2 of the light source, and a strong light source is required in relation to the sensitivity, and in the latter case, an in-plane intensity distribution is generated, so the spatial light modulator. It had the drawback that it required a very wide dynamic range.

[0005]

Therefore, an object of the present invention is to solve the above-mentioned conventional problems by providing a spatial light modulator using a liquid crystal on either of two surfaces sandwiching a modulation layer. Also has a structure having a photoconductive layer, a writing optical system is arranged on both sides, and reading is performed by a transmission type reading optical system.

[0006]

By using the above method, it is possible to provide a spatial light modulator capable of performing calculation and feedback between images with a simple optical system. By using this, a system such as an optical information processing system and an optical neural network can be realized more simply and more compactly than a conventional spatial light modulator.

[0007]

The present invention will be described in detail below with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic view showing the structure of an optical writing type spatial light modulator according to the present invention.

As the substrates 11a and 11b for sandwiching the liquid crystal, transparent glass substrates having a thickness of 5 mm whose both surfaces were polished to a parallel flatness of λ / 5 or less at He-Ne laser wavelength were used. ITO transparent electrode layers 12a and 12b were provided on the surfaces of both substrates. Hydrogenated amorphous silicon (a-Si: H) photoconductive layers 15a and 15b having a thickness of 2.5 μm were formed on the transparent electrode layers 12a and 12b. Further, on the surfaces of both substrates, an alignment film layer 13 was formed by oblique vapor deposition of silicon monoxide at an incident angle of 85 ° from the normal direction of the substrates and in a combined state so that the incident directions on both substrates coincide with each other.
a and 13b are provided.

Next, silica spheres having an average particle diameter of 1.0 μm are mixed and dispersed in the outer peripheral sealing material, and the sealing material is applied by printing using a letterpress printing method, and then two substrates are adhered to each other to narrow the liquid crystal. Created a holding gap. In this example, a ferroelectric liquid crystal composition was used as the liquid crystal. Ferroelectric liquid crystal composition
SCE-13 (manufactured by BDH) was used as 14, and after raising the temperature to the isotropic phase, vacuum injection was performed and the smectic C phase was gradually cooled to obtain a uniform alignment.

FIG. 2 is a diagram showing waveforms for driving the spatial light modulator according to the present invention. The waveform has a first pulse voltage 21 that erases the entire effective surface, a write pulse voltage 22 having a reverse polarity to the first pulse voltage, and a memory period 2.
3 is continuous. The spatial light modulator according to the present invention has a symmetrical structure having photoconductive layers on both sides of a liquid crystal modulation layer, and writing is performed from both sides simultaneously. Reading is performed transmissively using light of a wavelength that passes through the photoconductive layer.

FIG. 3 is a schematic equivalent circuit of the spatial modulator according to the present invention. The voltage VLC divided by the liquid crystal modulation layer varies depending on the resistances RPC1 and RPC2 of the photoconductive layer. The modulation layer using liquid crystal exhibits a non-linear response to VLC and has a threshold value. Therefore, the resistances RPC1 and RPC2 of the photoconductive layer change due to the change in writing light intensity, and optical modulation occurs when VLC exceeds the threshold value. In the region where the writing light strikes from both sides, both RPC1 and RPC2 are small, so that modulation occurs even with a relatively weak writing light intensity.

Even when the writing light is emitted from only one side, if the voltage VLC divided into the liquid crystal layer exceeds the threshold value, modulation occurs, but the other photoconductive layer remains at a high resistance, so that relatively strong writing is performed. Requires light intensity. By applying the above features, AND and OR operations can be performed in real time on two inputs by light including an image. The example is shown below.

FIG. 4 is a system diagram of an optical system in which writing and reading experiments were conducted. Halogen lamps were used as the writing light sources 41a and 41b, and the wavelength distribution was controlled through the interference filters 42a and 42b. The writing light is applied to each of two surfaces of the spatial light modulator 44 according to the present invention. When writing an image, masks were placed on 45a and 45b in the figure, and an image was formed on the input surface of the spatial light modulator 44 by the lens 46. The read light source 47 uses a semiconductor laser and is irradiated through the beam expander 48 and the polarizer 49 to the spatial light modulator 44 according to the present invention, modulated by the ferroelectric liquid crystal layer, and the analyzer 50.
The light is detected by and is observed by the CCD camera 51. The polarizer 49 is arranged in a direction in which the polarization plane is not modulated with respect to the stable state of the ferroelectric liquid crystal layer when the writing light is not irradiated, and the analyzer 50 crosses the transmitted light in the above state. It is located in. That is, the reading was set to be in the dark state in the absence of writing light. For the observation, the image captured by the CCD was displayed on the CRT 52 and photographed. In addition, the photodetector 53 was installed and the optical response was also measured. The driving was performed using a self-made driver 54.

The light source used for writing may be any one of a halogen lamp, a He-Ne laser, an Ar laser, and a semiconductor laser, but in this embodiment, the halogen lamp is used as a light source, the central wavelength is 600 nm, and the half width is half maximum. Light was passed through a 40 nm filter. The wavelength of the light used for the reading light is set so as to pass through the photoconductive layer. In this embodiment, since hydrogenated amorphous silicon is used as the photoconductive layer, a light source having a center wavelength of 700 nm or more such as a semiconductor laser is desirable. In this embodiment, a halogen lamp is used as a light source and a center wavelength of 830 nm,
Light passing through a filter having a half width of 80 nm was used.

The following writing experiment was conducted using the above system. 5 uses the optical system shown in FIG. 4 and uses images as shown in FIGS. 5A and 5B in the drawings as masks 45a and 45b of the writing optical system.
And OR are output. The reading light was continuously irradiated, the same driving waveform was used, and only the writing light amount was changed, and reading was performed in the continuous driving state. 5C is AND,
FIG. 5D has obtained the OR.

The driving waveform is as shown in FIG. 2. In this embodiment, + 10V, 2ms as erase pulse and -10V, 1ms pulse as write pulse are continuously applied, and further 7ms, 0V. A waveform having a continuous read period was used. The frame frequency is 100 Hz.

From this, it was found that by using the spatial light modulator according to the present invention, it is possible to simultaneously perform AND and OR operations between input images in the same plane. (Embodiment 2) In the spatial light modulator of the present invention, since the light receiving layers (photoconductive layers) are arranged on both sides of the modulation layer with respect to the traveling direction of the reading light, the feedback is read especially in the optical neural network or the like. It has the feature that it can be done from the side.

FIG. 6 is a conceptual diagram of an optical system for explaining the usefulness when the spatial light modulator according to the present invention is applied to a neural network. However, since the spatial light modulator according to the present invention in this embodiment uses the twisted nematic liquid crystal as the modulation layer, the response function is non-linear corresponding to the VT characteristic of the liquid crystal. When a ferroelectric liquid crystal is used as the modulation layer, the response function is binary, which corresponds to the McCulloch-Pitts model.

Input was made to the spatial light modulator 60 according to the present invention by using a writing optical system 61. The output was obtained by the light passing through the spatial modulator 60 by the first readout optical system which is a polarization optical system using the polarizer 62a and the analyzer 62b. The output was made to enter from the modulation layer side to the second spatial light modulator 63 using a ferroelectric liquid crystal as a modulation layer and having a photoconductive layer having sensitivity to the wavelength of the read light on only one side. . The second spatial light modulator was written by the authors in Japanese Patent Application Sho 63.
-68967 and the like, which uses a ferroelectric liquid crystal as the modulation layer, exhibits a binary response having a clear threshold value with respect to the incident light intensity. The image formed on the second spatial light modulator 63 is the spatial light modulator 60 according to the present invention.
The photoconductive layer of (1) uses a light source of a wavelength having sensitivity and is read by the second reading optical system 64 which is a polarization optical system that also serves as the analyzer 62b of the first reading optical system. The photoconductive layer on the side opposite to the input side of the spatial light modulator 60 is irradiated.

Here, in FIG. 6, the spatial light modulator 60 according to the present invention is a unit having a non-linear response function, and the writing light to the side irradiated with the reading light is the input to the neuron. Therefore, it is considered that this is synaptically connected to the unit. The reading light is modulated according to the writing light intensity, output to the second spatial light modulator, subjected to threshold processing, and then fed back to the spatial light modulator 60 according to the present invention as the second writing light. by this,
The response function to the input changes. This is done two-dimensionally in parallel on the plane of the spatial light modulator.

That is, the system of the embodiment shown in FIG. 6 is a system in which the input load is updated in real time by feedback. This shows that by using the spatial light modulator according to the present invention, the Hebb's learning rule, which is the basis of unsupervised learning in a neural network, is realized in real time and two-dimensionally in parallel.

[0022]

As described above, by using the spatial light modulator of the present invention, it is possible to execute a useful operation in optical information processing in real time, and learn Hebb in a neural network. The rules are realized in real time and two-dimensionally in parallel, which has the effect of dramatically increasing the range of applications.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structure of a liquid crystal spatial light modulator according to the present invention.

FIG. 2 is a diagram showing waveforms for driving a liquid crystal spatial light modulator according to the present invention.

FIG. 3 is a diagram showing a schematic equivalent circuit of the spatial light modulator according to the present invention.

FIG. 4 is a system diagram of an optical system in which writing and reading experiments are performed.

FIG. 5 is a schematic diagram showing an image between images using an image on each mask of a writing optical system using the spatial light modulator according to the present invention.
It is a photograph in which ND and OR are output.

FIG. 6 is a conceptual diagram of an optical system for explaining the usefulness when the spatial light modulator according to the present invention is applied to a neural network.

[Explanation of symbols]

 11a, 11b Substrate 12a, 12b Transparent electrode layer 13a, 13b Alignment film layer 14 Liquid crystal layer 15a, 15b Photoconductive layer 21 Erase pulse 22 Write pulse 23 Memory period 41a, 41b Write light source 42a, 42b Interference filter 44 Space according to the present invention Light modulator 45a, 45b Mask 46 Lens 47 Readout light source 48 Beam expander 49 Polarizer 50 Analyzer 51 CCD camera 52 CRT 53 Photodetector 54 Driver 60 Spatial light modulator 61 Writing optical system 62a Polarizer 62b Inspection according to the present invention Photon 63 Spatial light modulator 64 Second readout optical system

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Naoki Kato 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronics Co., Ltd. (72) Rieko Sekura 6-31-1, Kameido, Koto-ku, Tokyo No. Seiko Electronics Co., Ltd. (72) Inventor Teruo Ebihara 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronics Co., Ltd. (72) Shuhei Yamamoto 6-31-1, Kameido, Koto-ku, Tokyo No. Seiko Electronics Industry Co., Ltd.

Claims (16)

[Claims] 1. A set of substrates comprising a writing means by light, a reading means by light and a voltage applying means, wherein a photoconductive film is formed on a pair of transparent electrodes and a liquid crystal alignment film is formed on each opposing surface. Are opposed to each other, and a liquid crystal composition is sealed in the gap between them, which is a spatial light modulator. 2. The spatial light modulator according to claim 1, wherein the liquid crystal composition sealed in the gap is a ferroelectric liquid crystal composition. Modulator. 3. The spatial light modulator according to claim 1, wherein the liquid crystal composition sealed in the gap is a nematic liquid crystal composition. . 4. The spatial light modulator according to claim 2, wherein the gap is controlled within a range of 0.5 μm to 5 μm. 5. The spatial light modulator according to claim 1, wherein the photoconductive film is hydrogenated amorphous silicon. 6. The spatial light modulator according to claim 1, wherein the photoconductive films have different film thicknesses. 7. The spatial light modulator according to claim 1, wherein a dielectric mirror is formed between the photoconductive film and the liquid crystal alignment layer. Spatial light modulator. 8. The spatial light modulator according to claim 7, wherein the dielectric mirror has a different reflectance depending on a wavelength range. 9. The spatial light modulator according to claim 1, wherein the light writing means is arranged on either side of a pair of substrates of the spatial light modulator. The spatial light modulator according to claim 1. 10. The spatial light modulator according to claim 9, wherein the light writing means are independent optical systems, and the intensity is controlled independently. Spatial light modulator. 11. The spatial light modulator according to claim 9, wherein the light writing means is any one of a projection optical system, an image forming optical system, an interference optical system, and a Fourier optical system. The spatial light modulator according to claim 9, which is characterized in that: 12. The spatial light modulator according to claim 1, wherein the writing means using the light is an optical system that uses light transmitted through the spatial light modulator. Spatial light modulator. 13. The spatial light modulator according to claim 12, wherein the writing means by the light is a polarization optical system in which a polarizer and an analyzer are arranged before and after the spatial light modulator. The spatial light modulator according to claim 12. 14. The spatial light modulator according to claim 13, wherein the polarizer and the analyzer in the light writing means are arranged in crossed Nicols. Spatial light modulator. 15. The spatial light modulator according to claim 1, wherein the writing means using the light and the reading means using the light have different operating wavelengths. . 16. The spatial light modulator according to claim 15, wherein the wavelength used in the writing means by the light and the reading means by the light is the wavelength used in the reading means by the light. 16. The wavelength is longer than the wavelength used for the light writing means.
The spatial light modulator described.