JPH05196960A - Space optical modulator and driving method thereof - Google Patents

Abstract

PURPOSE:To increase an application range to both of a digital system and an analog system by developing the second threshold value which can exhibit a useful function and applying this value in optical information processing without using a special element structure. CONSTITUTION:The region where the writing light is stronger than the 1st threshold value 11 of the writing light intensity in the case of transition of one stable state in which ferroelectric liquid crystal molecules are stabilized to another stable state in the state in which the optical modulator constituted by combining a photoconductive layer consisting of hydrogenated amorphous silicon and an optical modulating layer consisting of a ferroelectric liquid crystal is not irradiated with the writing light is irradiated with the stronger writing light to develop the 2nd threshold value 12 to cause the transition to the one stable state and further, the first and second threshold values 11, 12 can be controlled by driving pulse widths, voltages and irradiation with bias beams. Then, there is an effect of exceedingly expanding the application range to both of the digital system and the analog system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photo-writing type ferroelectric liquid crystal spatial light modulator applied to an image processing device, a spatial light modulator for optical information processing and the like, and a driving method thereof.

[0002]

2. Description of the Related Art Conventionally, a spatial light modulator using a ferroelectric liquid crystal has been used as an element for intensity-modulating and outputting input image information in real time. In addition, the inventors
Japanese Patent Application No. 02-239594 also showed a driving method for obtaining an output having continuous gradation in the above device.

[0003]

However, depending on the conventional spatial light modulator using the ferroelectric liquid crystal and its driving method, each has only one threshold value for the writing light intensity, for example, 2 1 for input light (writing light)
Considering the digital logic of output light (reading light), it is not possible to obtain NAND or EOR even if AND or OR can be obtained by setting the input light intensity with respect to the threshold value, and several elements are cascaded. It was necessary to use a method such as connecting and synchronizing and using, which hindered application to optical computing and the like. Further, in the analog Fourier light information processing system, processing of the 0th order light,
Higher areas were not available in terms of dynamic range.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned conventional problems, and in a spatial light modulator using a ferroelectric liquid crystal and a driving method thereof, optical information processing without using a special element structure. In, it is possible to express a second threshold, which can show a useful function,
By applying this, the range of application will be dramatically increased for both digital and analog systems.

[0005]

In order to solve the above problems, according to the present invention, in a light modulator in which a hydrogenated amorphous silicon photoconductive layer and a ferroelectric liquid crystal light modulating layer are combined, the photoconductive film has a thickness of 0. Intrinsic hydrogenated amorphous silicon having a thickness of 1 to 5 μm, the ferroelectric liquid crystal layer has a thickness of 0.5 to 5 μm, and the maximum intensity of writing light is 0.01 mW on the writing surface. /
When writing is performed by constantly irradiating the reading light with light of cm ² or more, and the written image is read in the memory state, the ferroelectric liquid crystal molecules are stable in the state where the writing light is not radiated. Liquid crystal molecules in a region irradiated with stronger writing light in a region where the writing light is stronger than the first threshold of the writing light intensity when transitioning from one stable state to the other stable state However, on the contrary, the second threshold value that transits to the one stable state is expressed, and the first and second threshold values can be controlled by the drive pulse width, the voltage, and the irradiation of the bias light.

[0006]

By using the above method, two threshold values for the writing light intensity can be obtained and the values can be controlled. By using this, one element is used in digital optical information processing. Only by doing so, it is possible to realize all practical logic. Further, even in an analog system, removal of 0th order light can be easily performed. As a result, the application range of the ferroelectric liquid crystal spatial light modulator can be dramatically increased in both digital and analog systems.

[0007]

The present invention will be described in detail below with reference to the drawings. FIG. 3 is a schematic diagram showing the structure of an optical writing type ferroelectric liquid crystal spatial light modulator according to the present invention. As the substrates 31a and 31b for sandwiching liquid crystal molecules, transparent glass substrates with a thickness of 5 mm whose both surfaces were polished to a parallel flatness of λ / 5 or less at a He-Ne laser wavelength were used. ITO transparent electrode layers 32a and 32b were provided on the surfaces of both substrates. A 2.5 μm thick hydrogenated amorphous silicon (a-Si: H) photoconductive layer 35 was formed on the transparent electrode layer 32a on the light writing side. Furthermore, the surface of both boards is 85 degrees from the normal direction of the boards.
Orientation film layers 33a and 33b in which silicon monoxide was obliquely vapor-deposited were provided so that the incident directions on the write-side and read-side substrates coincided with each other at an incident angle of ° and combined.

Next, silica spheres having an average particle diameter of 1.0 μm are mixed and dispersed in the outer peripheral sealing material, the sealing material is applied by printing using a letterpress printing method, and then two substrates are adhered to each other to obtain a ferroelectric property. A gap for holding the liquid crystal was formed. Ferroelectric liquid crystal composition
As 34, SCE-13 (manufactured by BDH) was used. After the temperature was raised to the isotropic phase, vacuum injection was performed and the smectic C phase was gradually cooled to obtain a uniform orientation.

FIG. 4 is a system diagram of an optical system in which writing and reading experiments were conducted. A He-Ne laser (maximum output 150 mW) manufactured by NEC was used as the writing light source 41, and the intensity was controlled through the polarizing plate 42. Writing light is mirror 43
The light is reflected by a and 43b, and is obliquely applied to the ferroelectric liquid crystal spatial light modulator 44 according to the present invention. (The beam expander 45a of 10 times may be inserted in the optical path of the writing light.) The reading light source 46 uses a Heles-Ne laser (output 10 mW) made by Melles Griot, and the ND filter 47 for adjusting the light amount. 10x beam expander 45b,
It is irradiated to the ferroelectric liquid crystal spatial light modulator 44 according to the present invention through the beam splitter 48, and is reflected by the interface between the ferroelectric liquid crystal layer and the hydrogenated amorphous silicon photoconductive layer while being modulated by the ferroelectric liquid crystal layer. , Enters the beam splitter 48 again.

Here, the light reflected by the beam splitter surface is detected by the polarizing plate 49 and observed by the CCD camera 50. The reading light source 46 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 polarizing plate 49 crosses the reflected light in the above state. It is located in. That is, the reading is in the dark state in the absence of the writing light. CCD observation
The image captured by the camera 50 was displayed on the CRT 51 and photographed. Further, the photodetector 52 was placed instead of the CCD camera 50, and the optical response was also measured. The driving was performed using a self-made driver 53.

The light source used for writing is He-
It is any one of a Ne laser, an Ar laser, a semiconductor laser, and a halogen lamp, and the light source used for the reading light may be any one of a He—Ne laser, an Ar laser, a semiconductor laser, and a halogen lamp. The following writing experiment was conducted using the above system.

FIG. 1 shows a spatial light modulator according to the present invention.
6 is a graph showing the read light intensity in the case of reading in a memory state by changing the write light intensity while continuously irradiating the write light of 4.63 μW / cm ² . Since the light modulation layer using the ferroelectric liquid crystal has bistability and has the read light intensity in the memory state, the read light is obtained in the binary state of the bright state and the dark state, and A first threshold value 11 that transitions from a dark state to a bright state and a second threshold value 12 that transitions from a bright state to a dark state are obtained as the writing light intensity increases. In this embodiment, the bias light is not emitted, and the drive waveform is the erase pulse +9.15.
V2.5 ms, write pulse −9.15 V2 ms, frame frequency 100 Hz. The first threshold appears near the writing light intensity of 0.2 mW / cm ² , and the second threshold appears near the writing light intensity of ² mW / cm ² .

FIG. 2 shows a spatial light modulator according to the present invention.
He-Ne laser beam (75 mW made by NEC) while continuously irradiating the writing light of 4.63 μW / cm ^2.
Is a photograph of a read image in the case of irradiating as a writing light in a state where the intensity is weakened to 3.14 μW in the center 200 μm pinhole, and reading is performed in a memory state. Bias light is not emitted and the drive waveform is erase pulse +9.15
V, 2.5 ms, write pulse-9.15 V, 2 m
s, the frame frequency is 100 Hz. The photograph is an image captured by the CCD, displayed on the CRT, and the screen of the CRT is taken. Therefore, a horizontal line corresponding to the scanning line of the CRT is visible in the photograph. From the photograph, it can be seen that only the ring-shaped portion 21 that is equal to or greater than the first threshold value and equal to or less than the second threshold value is inverted and stored in the bright state. The central portion 22 having the writing light intensity equal to or higher than the second threshold had exactly the same reflectance as the peripheral dark-state portion 23 equal to or lower than the first threshold. It should be noted that the fact that the contour of the portion on the ring is disturbed in the photograph is due to the intensity distribution of the writing light, and no problem occurs in an actual system.

This clearly demonstrated the expression of the first and second thresholds.

[0015]

As described above, according to the method of the present invention, a photo-writing type liquid crystal spatial light modulator using a ferroelectric liquid crystal is useful in optical information processing without using a special element structure. It is possible to express a second threshold value that can exhibit a function, and by applying this, there is an effect of dramatically increasing the range of application in both digital and analog systems.

[Brief description of drawings]

FIG. 1 is a graph showing the read light intensity when the spatial light modulator according to the present invention is read in a memory state by changing the write light intensity while continuously irradiating the write light.

FIG. 2 is a drawing-substituting photograph of a read-out image when a spatial light modulator according to the present invention is irradiated with a writing light and a He—Ne laser beam is irradiated as the writing light and is read in a memory state.

FIG. 3 is a schematic diagram showing the structure of an optical writing type ferroelectric liquid crystal 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.

[Explanation of symbols]

11 First Threshold 12 Second Threshold 21 Bright State Part (First Threshold or More and Second Threshold or Less) 22 Dark State Part 1 (Second Threshold or More) 23 Dark State Part 2 (Parts Below First Threshold) 31a, 31b Transparent Substrates 32a, 32b Transparent Electrodes 33a, 33b Alignment Film Layer 34 Ferroelectric Liquid Crystal Layer 35 Photoconductive Film 41 Writing Light Source 42 Polarizing Plates 43a, 43b Mirror 44 Ferroelectric Liquid Crystal Spatial light modulator 45a, 45b Beam expander 46 Readout light source 47 ND filter 48 Beam splitter 49 Polarizing plate 50 CCD camera 51 CRT 52 Photodetector 53 Driver

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

Claims (7)

[Claims] 1. A glass substrate having a photo-conductive film formed on a transparent electrode and a glass substrate having a transparent electrode, which are provided with a light-writing device, a light-reading device, and a voltage applying device, which face each other. In a ferroelectric liquid crystal spatial light modulator in which a pair of glass substrates having a liquid crystal alignment film formed on their surfaces are opposed to each other and a ferroelectric liquid crystal composition is sealed in the gap, the photoconductive film has a thickness of 0. Intrinsic hydrogenated amorphous silicon having a thickness of 1 to 5 μm, the ferroelectric liquid crystal layer has a thickness of 0.5 to 5 μm, and the intensity of writing light is 0.01 mW at the maximum value on the writing surface. / Cm ² or more of light, writing is performed while irradiating the reading light all the time, and when reading the written image in the memory state, it is urged without the writing light being radiated. A region where the writing light is stronger than the first threshold of the writing light intensity when the electronic liquid crystal molecule is stabilized and transits from one stable state to the other stable state. 2. The spatial light modulator according to claim 1, wherein the ferroelectric liquid crystal molecule has a second threshold value that causes the liquid crystal molecule to transit to the one stable state. 2. A dielectric mirror for light separation is formed between the photoconductive film and the liquid crystal alignment layer.
The spatial light modulator described. 3. The applied drive voltage is determined from a first pulse voltage for erasing, a second pulse voltage for writing having a polarity opposite to that of the first pulse voltage, and a memory period. The reading is performed during the memory, and the pulse width or pulse height of the first and second pulse voltages is controlled separately to control the first and second thresholds. 2. The method for driving the spatial light modulator according to 1. 4. A crossed Nicol is arranged in the readout optical system, and the liquid crystal molecules are arranged so that the arrangement direction of the liquid crystal molecules determined by the first pulse voltage is in a bright or dark field state under the crossed Nicols. 4. The method for driving a spatial light modulator according to claim 3, wherein: 5. A bias light is irradiated from a writing side or a reading side in addition to a light source used for writing and reading light, and the first and second threshold values are controlled by controlling the intensity of the bias light. The method of driving a spatial light modulator according to claim 1, wherein 6. The method for driving a spatial light modulator according to claim 1, wherein the writing optical system used has a shutter in the system, and the writing light is not irradiated at the time of reading. 7. The writing optical system used comprises two or more systems whose intensity can be controlled independently, and two or more images are simultaneously irradiated on the same writing surface. Driving method for spatial light modulators.