JPH06273794A - Liquid crystal spatial optical modulator and its driving method - Google Patents

Abstract

PURPOSE:To express gradations even in a memory state by forming a liquid crystal compsn. to be used as a modulating material of a ferroelectric liquid crystal compsn. exhibiting the intrinsic pitch smaller than the thickness of a liquid crystal layer and a chiral smectic phase at ordinary temp. having specified or higher spontaneous polarization. CONSTITUTION:A pair of glass substrates 11a, 11b constituted by forming liquid crystal oriented films 13a, 13b on the respective opposite surfaces of a glass substrate 11a having a photoconductive film 15 formed on it on a transparent electrode 12a and a glass substrate 11b having a transparent electrode 12b formed on it are arranged to face each other and the liquid crystal compsn. 14 is sealed in the spacing therebetween. The photoconductive film 15 is a hydrogenated amorphous silicon having 0.5 to 3.5mum thickness. The liquid crystal layer has 0.5 to 3mum thickness. The liquid crystal compsn. 14 is a ferroelectric liquid crystal compsn. having the intrinsic pitch smaller than the thickness of the liquid crystal layer and >=30nc/cm<2> spontaneous polarization and exhibiting the chiral smectic phase at ordinary temp. The control of the gradation characteristic even in the memory state is enabled by controlling the intensity of the bias light to be projected from the writing side or reading-out side.

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 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 liquid crystal has been used as an element for intensity-modulating and outputting input image information in real time. Generally, a binarization device using a surface-stabilized ferroelectric liquid crystal as a modulation material is known. The authors have also shown, in Japanese Patent Application No. 02-239594, 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 surface-stabilized ferroelectric liquid crystal and its driving method, the method as disclosed in Japanese Patent Application No. 02-239594 is used. Although it is possible to express gradation in the continuous driving state by using it, it is impossible to express gradation in the memory state.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention solves the above-mentioned problems by using a spatial light modulator using a liquid crystal and a method of driving the same. Even in the memory state, the liquid crystal composition used as a material is a ferroelectric liquid crystal composition that exhibits a chiral smectic phase at room temperature and has an intrinsic pitch smaller than the liquid crystal layer thickness and a spontaneous polarization of 30 nc / cm 2 or more. It is possible to express gradation.

[0005]

FIG. 3 shows changes in the read light intensity with respect to the write light intensity in the conventional spatial light modulator using the surface-stabilized ferroelectric liquid crystal and the spatial light modulator according to the present invention. In (a), a spatial light modulator using a conventional surface-stabilized ferroelectric liquid crystal,
(B) shows a spatial light modulator according to the present invention.
As is clear from comparison between (a) and (b), in (b), there is a portion where the change of the reading light intensity is gentle with respect to the increase of the writing light intensity. This portion is indicated by an arrow as a range 31 in which gradation is displayed. In this range,
It is observed that as the writing light intensity increases, the number of small inversion domains is generated in the plane and gradually increases, and finally, all the planes are inverted. Moreover, each of these small inversion domains is stable in that state and has a memory property. By utilizing such characteristics, it is possible to realize a spatial light modulator that can maintain gradation even in the memory period within the range 31 in which gradation is represented,
Therefore, the application range of the ferroelectric liquid crystal spatial light modulator can be dramatically increased.

[0006]

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing the structure of a spatial light modulator according to the present invention. A glass substrate 11a for sandwiching liquid crystal molecules,
As 11b, a transparent glass substrate having 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, was used. ITO transparent electrode layers 12a and 12b were provided on the surfaces of both substrates. 2.5 on the transparent electrode layer 12a on the writing side by light
A hydrogenated amorphous silicon (a-Si: H) photoconductive film 15 having a thickness of μm was formed. The light separating dielectric mirror is formed on the photoconductive film 15. Further, nylon was applied to the surfaces of both substrates and subjected to rubbing treatment, and in the combined state, alignment film layers 13a and 13b were provided so that the rubbing directions on the writing side and reading side substrates were aligned. The alignment film may be a polyimide film, and rubbing may be performed on one side only.

The photoconductive film 15 can be made of other materials such as cadmium sulfide without any problem, and the optimum film thickness varies depending on the thickness of the dielectric mirror and the liquid crystal layer. The thickness is set within the range of up to 3.5 μm in consideration of the electrical characteristics and film thickness of each film.

Next, silica spheres having an average particle diameter of 1.8 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 layer 14 was formed. The ferroelectric liquid crystal composition has an intrinsic pitch of 0.3 μm and a spontaneous polarization of 100.
Using a composition of nc / cm2, 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. 2 shows the waveform of the method for driving the spatial light modulator according to the present invention. The waveform is a series of a first pulse 21 for erasing the effective surface, a second pulse 22 having a polarity opposite to that of the first pulse for writing, and a memory period 23. To be done. When the intensity of the bias light emitted from the writing side or the reading side is changed, the voltage divided in the ferroelectric liquid crystal layer changes accordingly. At this time, when the conventional surface-stabilized ferroelectric liquid crystal is used as the modulation material, when the divided voltage reaches a certain threshold value, the liquid crystal molecules on the entire effective surface are inverted, so that a gradation may be displayed. I couldn't
When the ferroelectric liquid crystal of the spatial light modulator of the present invention is used as a modulation material, it inverts while not generating a steep threshold value with respect to voltage and generating partial domains, so that until the entire inversion, The gradation is shown in. By utilizing such characteristics, it is possible to control the gradation by controlling the intensity of bias light emitted from the writing side or the reading side.

In this embodiment, a liquid crystal composition having a characteristic pitch of 0.3 μm was used for a gap of 1.8 μm. However, if the characteristic pitch is smaller than the gap, other characteristics will be considered without any problem. You can set the value. If the specific pitch is larger than the gap, a surface-stabilized state occurs, and an alignment state in which halftone is generated cannot be obtained. Further, the value of spontaneous polarization is 100 nc / cm 2 in this embodiment, but 30 nc in order to have a practically wide range in which halftone can be obtained.
/ Cm 2 or more, and may be arbitrarily set at a value higher than this.

FIG. 4 shows an example of a reading optical system of the spatial light modulator according to the present invention. The readout light 41 passes through the lens 42, the interference filter (center wavelength 633 nm) 43, the polarizer 44, and is reflected by the beam splitter 45, and then the imaging lens 46.
The read light side of the spatial light modulator 47 is irradiated therethrough, and the writing light 48 emits the writing light 48 through the lens 49 and the interference filter (center wavelength 53
(0 nm) 50, film 51, and the information formed by the imaging lens 52 on the writing surface of the spatial light modulator 47 is reflected on the hydrogenated amorphous silicon surface by this read light, and passes through the analyzer 53 and the lens 54. It is taken into the light receiving element 55. At this time, the polarizer 44 that makes the readout light linearly polarized light
When the analyzer 53 for detecting the reflected light modulated by the ferroelectric liquid crystal layer is set to the crossed Nicol state and the white light is used as the reading light, the first driving method shown in FIG. Spatial light modulator so that the alignment direction of liquid crystal molecules determined by the pulse voltage is a dark field under crossed Nicols
47 are located. A photo detector 56 was installed to measure the optical response.

FIG. 5 is a system diagram of an optical system in which writing and reading experiments were conducted. The light flux emitted from the writing light source 61 is adjusted to have a predetermined amount by the ND filter 62 and then expanded to a predetermined diameter by the beam expander 63.
4. The input image is formed on the writing surface of the spatial light modulator 66 through the lens 65. Further, the parallel light flux emitted from the readout light source 67, passed through the liquid crystal shutter 68, and expanded to a predetermined diameter by the beam expander 69, is a beam splitter.
Irradiates the reading surface of the spatial light modulator 66 through 70, 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, and enters the beam splitter 70 again. To do. Here, the light reflected by the surface of the beam splitter 70 is analyzed by the analyzer 71, and the lens 72
And is taken into the light receiving element 73. This reading optical system is set so that 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 71 changes the reflected light in the above state. In contrast, they are arranged in a cross. That is, the reading is in the dark state in the absence of the writing light. Further, it is possible to control the gradation by irradiating the entire surface of the spatial light modulator 66 on the writing side with the bias light 74 and controlling the intensity of the bias light. The bias light may be applied to the entire reading surface of the spatial light modulator. The spatial light modulator used in this embodiment is not provided with a dielectric mirror for light separation, but even in the case of the spatial light modulator with a dielectric mirror, the read-out light irradiated is the ferroelectric liquid crystal layer. The same thing can be achieved only by being reflected at the interface of the light separating dielectric mirror.

[0013]

As described above, according to the method of the present invention, in the photo-writing type liquid crystal spatial light modulator using the ferroelectric liquid crystal and the driving method thereof, the gray scale can be set even in the memory state. This has the effect of enabling expression and thus dramatically increasing the range of applications of ferroelectric liquid crystal spatial light modulators.

[Brief description of drawings]

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

FIG. 2 is a waveform showing a driving method of a liquid crystal spatial light modulator according to the present invention.

FIG. 3 is a diagram showing a change in read light intensity with respect to write light intensity.

FIG. 4 is a diagram showing an example of a readout optical system of a liquid crystal spatial light modulator according to the present invention.

FIG. 5 is a system diagram of an optical system in which writing and reading experiments are performed.

[Explanation of symbols]

 11a, 11b Glass substrate 12a, 12b Transparent electrode layer 13a, 13b Alignment film layer 14 Ferroelectric liquid crystal layer 15 Photoconductive film 16 Writing light 17 Reading light 21 First pulse 22 Second pulse 23 Memory period 31 Gradation Range 41 Read light 42 Lens 43 Interference filter (center wavelength 633 nm) 44 Polarizer 45, 57 Beam splitter 46 Imaging lens 47 Spatial light modulator 48 Writing light 49 Lens 50 Interference filter (center wavelength 530 nm) 51 Film 52 Imaging Lens 53 Analyzer 54 Lens 55 Light receiving element 56 Photodetector 58 Driver 61 Writing light source 62 ND filter 63, 69 Beam expander 64 Input image film 65 Lens 66 Spatial light modulator 67 Readout light source 68 Liquid Shutter 70 beam splitter 71 analyzer 72 lens 73 light-receiving elements 74 bias light 75 monitor 76 Driver

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuhei Yamamoto 6-31-1, Kameido, Koto-ku, Tokyo Seiko Denshi Kogyo Co., Ltd.

Claims (5)

[Claims] 1. A glass substrate on which a photoconductive film is formed on a transparent electrode and a glass substrate on which a transparent electrode is formed, each of which is provided with a light writing device, a light reading device, and a voltage applying device. In a liquid crystal spatial light modulator in which a pair of glass substrates having a liquid crystal alignment film formed on the surface thereof are arranged to face each other, and a liquid crystal composition is sealed in the gap,
The photoconductive film is hydrogenated amorphous silicon having a thickness of 0.5 to 3.5 μm, and the liquid crystal layer is 0.5 to 3 μm.
The liquid crystal composition has a thickness of m and is a ferroelectric liquid crystal composition exhibiting a chiral smectic phase at room temperature having an intrinsic pitch smaller than the thickness of the liquid crystal layer and a spontaneous polarization of 30 nc / cm 2 or more. Liquid crystal spatial light modulator. 2. The applied drive voltage comprises a first pulse voltage for erasing, a second pulse voltage having a polarity opposite to that of the first pulse voltage for writing, and a memory period. The method for driving a liquid crystal spatial light modulator according to claim 1. 3. A light separation dielectric mirror is formed between the photoconductive film and the liquid crystal alignment layer.
The liquid crystal spatial light modulator described. 4. The liquid crystal molecules are arranged in a reading optical system set in crossed Nicols and arranged so that the alignment direction of liquid crystal molecules determined by the first pulse voltage is in a dark field state under crossed Nicols. 3. The method according to claim 2,
A method for driving the described liquid crystal spatial light modulator. 5. The method of driving a liquid crystal spatial light modulator according to claim 1, wherein the reading optical system used has a shutter in the system, and the reading light is not irradiated at the time of writing.