JPH0320719A - Optical write type liquid crystal light valve - Google Patents

Abstract

PURPOSE:To write an image with high storage performance and high resolution while suppressing its lateral expansion by driving a photoconductive layer, formed on the transparent electrode on an optical write side, to a size within a specific range. CONSTITUTION:Transparent electrodes 3 and 4 are liquid crystal orienting films 5 and 6 are formed on the surfaces of transparent substrates 1 and 2 and a ferroelectric liquid crystal layer 7 is inserted between the films 5 and 6. Then the photoconductive layer 9 which is divided by insulators 10 to a 4 - 40mum<2> size is formed on the electrode on the optical write side. The light valve which is thus formed is applied with a DC bias voltage generated by superposing a high-frequency AC waveform to write an image, and then a sharp image of the same level as that when only a direct current is applied to an undivided light valve is obtained. Further, an excellent memory having no expansion of the liquid crystal molecule array state of an unwritten part is obtained. Consequently, high-resolution writing which is free from DC defect is enabled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an intermediate recording medium of an optical printer, an image display device,
The present invention relates to an optically writable liquid light valve using ferroelectric liquid crystal that is applied to optical shunters, image processing devices, optical information processing systems, and the like.

[Summary of the invention]

The present invention provides highly sensitive light guide 7J. This paper concerns the structure of the photoconductive layer of an optically writable liquid light valve that combines a ferroelectric liquid crystal with bistable memory properties and a ferroelectric liquid crystal with bistable memory properties. Conventionally, photoconductive films used in optically written liquid crystal light valves have been formed uniformly over the entire surface of the optical writing side electrode by sputtering, vacuum evaporation, glow discharge decomposition, etc. At times, when an AC driving waveform is applied, the impedance of the photoconductive layer decreases, causing the pattern to be written to spread laterally, impairing resolution, but as in the present invention,
By dividing the photoconductive layer into sizes ranging from 4μm to 400μm2 using photolithographic etching method, mask evaporation method, mask spattering method, etc.
It becomes possible to dramatically improve the resolution, and it is possible to provide an extremely high-performance optical writing type liquid crystal light valve.

In addition, hydrogenated amorphous silicon, which has high photosensitivity and large carrier mobility, is extremely effective as a photoconductive film, and by combining it with ferroelectric liquid crystal, it can be used not only for writing with halogen light, but also for low-power writing. It is also possible to realize an optical writing type liquid crystal light bulb that can perform extremely high-speed, high-resolution, and high-contrast writing using a semiconductor laser.

[Conventional technology]

For optical writing type light valves, various studies have been conducted on the adrenosing method and the display mode of the liquid crystal used. Among them, liquid crystal light valves that combine twisted nematic mode, electric field-controlled birefringence mode, and photoconductive film have characteristics close to practical level, and are used in incoherent-coherent converters for optical information processing, etc. ing. However, in these modes, there is no memorability of the written image, and the image disappears when the writing light is removed. Even when writing digitally with a beam spot such as a laser beam, the retention time of the image of the written area is short, so it is not possible to increase the resolution, and when trying to obtain a high-resolution large screen display, it is impossible to increase the resolution. It is necessary to overwrite the image many times at high speed, which requires the development of an ultra-high-speed, ultra-high-precision laser scanner and an ultra-sensitive photoconductive film, which is extremely difficult to achieve. be. A combination of the cholesteri-Sochnematic phase transition mode and a photoconductive film has memory properties, but has the disadvantages of slow writing speed and low contrast.

In recent years, we have focused on ferroelectric liquid crystals that have the potential to exhibit excellent properties such as high-speed response, memory performance, high contrast, and wide viewing angles, and have developed an optical writing type that combines ferroelectric liquid crystals and photoconductive 1i films. Liquid crystal light halves are now being actively researched.

In either case, the photoconductive film is usually coated onto a transparent electrode made of ITO or the like for optical writing using a method such as a spasoter method, a vacuum evaporation method, or a glow discharge decomposition method, to a thickness of several tens to several tens of meters uniformly over the entire surface. It was formed of. [Problems to be Solved by the Invention] However, when optically writing the necessary information to the optically written liquid crystal light bulb described above, an AC voltage waveform is used as the write drive waveform in most cases, and large spontaneous polarization occurs. Even when using ferroelectric liquid crystals, which have molecular inversion due to spontaneous polarization reversal depending on the polarity, in order to prevent alignment defects or improve reliability, it is necessary to
A DC bias voltage waveform on which an AC waveform of approximately Q k fiz is superimposed is often used. However, when an alternating current voltage is applied, the impedance of the photoconductive film becomes low, the optically written image spreads in the lateral direction, and there is a problem in that the resolution decreases. When using ferroelectric liquid crystals, high-resolution writing is expected because the liquid crystal layer is thin, but it has been difficult to obtain the expected resolution. Furthermore, ferroelectric liquid crystals have the disadvantage that molecules tend to flow in the layer direction, which tends to impair memory properties.

[Means to solve the problem]

In order to solve the above problem, the present invention divides the photoconductive layer formed on the transparent electrode on the optical writing side into sizes of 4 μm to 400 μm, thereby suppressing the spread of the written image in the lateral direction. In addition, high-resolution writing is made possible by improving memory performance.

[Effect]

In the liquid crystal light valve of the present invention, once the entire writing surface of the liquid crystal light valve is irradiated with light, a DC high voltage sufficiently higher than the threshold voltage of the photoconductive layer during the bright period or 1001{z
Apply a DC bias voltage superimposed with an AC voltage of 5Qkflz to align the ferroelectric liquid crystal to a stable state in one direction, or apply a DC bias voltage sufficiently higher than the dark value voltage without irradiation with light, or, 100Bz to 50k
After going through the first step of applying a DC bias voltage superimposed with an AC voltage of Hz to align the ferroelectric branch crystals to a stable state in one direction, the voltage is below the dark value voltage in the dark without light irradiation,
At the time of light irradiation, a DC bias voltage of opposite polarity or an AC voltage of 100 h to 5QkHz, which is higher than the dark value voltage, is not applied, and optical writing is performed using a laser beam or the like.
Image writing is performed through the steps. Photocarriers are generated in the photoconductive layer in the area irradiated with light, and the generated carriers drift in the direction of the electric field due to the DC bias voltage.As a result, the resistance of the photoconductive layer decreases, and in the area irradiated with light, photocarriers are generated. A voltage of opposite polarity higher than the dark value voltage is applied, and the liquid crystal molecules are reversed due to the reversal of spontaneous polarization, and the other stable state is written. The image formed in this way consists of irradiation with linearly polarized projection light whose polarization axis is aligned with the alignment direction (or perpendicular direction) of the liquid crystal molecules aligned in the first step, and polarization of the reflected light by the reflective layer. It can be read out on a screen by projection through an analyzer placed so that the polarization axis is perpendicular (or parallel) to the direction. By using a waveform in which an alternating current voltage is superimposed, it is possible to solve the problem of structural defects, so-called DC defects, where the arrangement of liquid crystal molecules near the alignment film is broken and the liquid crystal molecules no longer respond to the applied voltage. It is possible to improve reliability.

〔Example〕

The contents of the present invention will be explained in detail below using the drawings.

FIG. 1 is a sectional view showing the structure of a liquid crystal light valve according to the present invention.

The transparent substrate 1.2 has transparent electrodes 3, 4 . Liquid crystal alignment film 5
．． 6 is provided. The transparent substrates 1 and 2 have their alignment films 5.6 facing each other, and il! ! A dielectric liquid crystal N7 is sandwiched between them.

On the transparent electrode 4 on the side where optical writing is performed, a photoconductive layer 9 is formed divided by an insulator 10, and a dielectric mirror 8 as a light reflecting layer is laminated thereon.

According to the liquid crystal light valve as described above, writing is performed on the ferroelectric liquid crystal layer 7 by the writing light l1 from the outer surface, and the written optical information can be read out by the projection light l2.

FIG. 2 is a schematic diagram showing a divided structure of a photoconductive layer according to the present invention, and 13a. 13b is a photoconductive layer divided into squares and circles, respectively, and 14a and 14b are insulators for filling the divided gaps.

In the example, first, a plate is prepared as the transparent substrate 1.2, and ITOyi with a thickness of 500 mm is used as the transparent electrode 3.4.
A bright electrode was formed. On the optical writing side transparent electrode layer 4, a 4-thick intrinsic hydrogenated amorphous silicon (a-Si:H) is formed by discharge decomposition of a gas mainly composed of SiF4, and the photoconductive layer 9 and did. Thereafter, using a photolithography method, the photoconductive layer was divided into 4n×4 pieces as shown in 13a. Thereafter, in order to level the surface, a polycarbonate film dissolved in tetrahydrofuran was coated with a thickness of 0.3 mm using a doctor blade, and the gaps between the etched parts were filled and the insulating layer 10,
143 was formed, and the photoconductive layer was divided. On the thus formed divided photoconductive layer, silicon (St
) and silicon dioxide (Sing) were laminated to form a dielectric mirror 8. Silicon monoxide (Sin) was placed on the dielectric mirror 8 and the transparent substrate 3 on the projection side at an angle of 82 degrees to the normal direction of the substrate, and with a film thickness meter centered in the normal direction of vapor deposition. The liquid crystal alignment layers 5 and 6 were formed by oblique vapor deposition to a thickness of 2000 mm. The transparent substrate 1.2 has its alignment layers 5 and 6 facing each other, and a gap of 2.5 mm is separated by a spacer made of adhesive to which glass spheres with a diameter of 1.5 mm are added. 01! III to t! The dielectric liquid crystal 7 was held between the two by adhesion. The encapsulated ferroelectric liquid crystal composite is a ferroelectric liquid crystal composite obtained by adding an optically active substance to an ester-based SmC liquid crystal mixture.
-((4"-octyl)phenyl)benzoic acid (3"-fluoro, 4"-octyloxy)phenyl ester,
4-((4'-octyloxy)phenyl)benzoic M(
A 1:1 mixture of 3"-fluoro54"-octyloxy)phenyl ester was used, and to this was added 5-octyloxynaphthalenecarboxylic acid and 1 as optically active substances.
A ferroelectric liquid crystal composition was prepared by adding 25% by weight of '-cyanoethyl ester.

Figure 3 shows the voltage-light reflection when a voltage is applied between the electrodes while irradiating the entire surface with halogen light from the optical writing side using the optically written liquid light valve formed in this way. This shows the rate characteristics. In this case, the optical conductive layer is in a conductive state (low resistance Li) over the entire surface,
The applied voltage is mostly applied to the ferroelectric liquid crystal. The voltage waveform used was a 0.1Hz, 20VF-P triangular wave. As is clear from the figure, the liquid crystal light valve according to the present invention exhibits relatively clear threshold characteristics and bistability. However, when observing this liquid crystal light bulb with a polarizing microscope,
It was confirmed that over time, the so-called DC defect region, in which inversion of liquid crystal molecules becomes difficult to occur, expands, the arrangement of molecules becomes non-uniform, and the overall contrast deteriorates.

FIG. 4 shows the same optical writing type liquid crystal light valve being used to illuminate the entire surface with halogen light at 3kHz, 20V. This figure shows the voltage-light reflectance characteristics when a 20VP-P triangular wave is applied while superimposing a rectangular wave of . As is clear from the figure, it can be seen that by superimposing alternating current on the triangular wave, more clear bistability appears. Also, when observed under a polarizing microscope, the alignment of the liquid crystal molecules was uniform throughout, and no DC defects were observed.

Next, using a conventional optical writing type liquid crystal light valve that does not divide the photoconductive layer, the image formed on the mask l7 is exposed to the liquid crystal light valve 18 by a system using a polarizing microscope, as shown in FIG. I wrote. In this case as well, when writing with only a DC bias, DC defects occur, and the written image has uneven contrast due to non-uniform alignment of liquid crystal molecules, and when alternating current is superimposed,
It was possible to write an image with good contrast without such a phenomenon occurring. However, the sharpness of the edge of the image during writing is worse than when only DC is used, and it is written in a slightly smeared form. The alignment state of liquid crystal molecules in the non-written area spread in the layer direction, and the memory properties were not very good. By similar means, a photoconductive layer according to the invention of 4μ×4−
Using an optical writing type light valve divided by the size of
When optical writing was performed while applying a DC bias voltage with a 25VP-P AC waveform superimposed, the sharpness of the edge portion of the image was confirmed by using a conventional optical writing type liquid crystal light valve that does not divide the photoconductive film. The level was almost the same as when writing using direct current only. Furthermore, it was found that when the voltage is left open after writing and memory is performed, the alignment state of liquid crystal molecules in the non-written area does not spread in the layer direction, resulting in an extremely good memory state. The division shape of the photoconductive layer is
In addition to the square shown in FIG. 2 138, the circular shape shown in FIG. 2 13b, any rectangular shape may be used, and from the viewpoint of resolution, the appropriate dividing size is 4 μm 2 to 400 μm.

Methods for forming the photoconductive film in sections include, in addition to the above-mentioned photolithography method, methods such as vacuum evaporation and spuntering using a fine mask. Although it is preferable that the division be completed completely, there is almost no problem even if the division is partially connected. However, if the gap between the photoconductive layers is too wide, the effective area will become small, which will conversely impair resolution.

Therefore, the gap between the photoconductive layers should be approximately 1 to 2. It is desirable to keep it in check. As a photoconductive layer, it has high resistance in the dark,
Highly sensitive hydrogenated amorphous silicon (a-Si:H), which has a significantly lower resistance when irradiated with light, is suitable for this optically written liquid crystal light valve, and can be easily divided by photolithography. Alternatively, a mask may be placed on ITO and vacuum evaporation of CdS, Se-Te, etc. may be performed to form divided photoconductive layers. Insulators that fill the gaps between the divided photoconductive layers include, in addition to polycarbonite, organic polymer materials with relatively good heat resistance and high resistivity such as polyimide and polyamide, as well as SiO. Inorganic materials such as ZrO may also be used. The film thickness of a-Si:H is such that there are no bin holes, the photosensitivity is uniform, and the resistivity of a-Si:H in the dark is 1011 to 10'! Ω0, and the resistivity of the ferroelectric liquid crystal is about 10” to IQ1!Ωcra, so when considering the partial voltage ratio, it is desirable to have a thickness of 21 or more, which is about the same as the thickness of the ferroelectric liquid crystal layer. Considering, 10J
IM is considered to be the upper limit.

Next, the liquid crystal light valve of the present invention is made into an incoherent light valve.
An example of application as a coherent converter will be explained. FIG. 6 is a conceptual diagram of a coherent optical correlation system using the liquid crystal light valve of the present invention. The reflected light from the measurement object I9 is imaged by a lens 20 onto a liquid crystal light valve 21 related to the present invention. The liquid crystal optical element according to the present invention has a larger area than one using a nonlinear optical crystal, so it can be used even when measuring a large object. Because the response speed is faster than that of previous models, high-speed processing close to real time is possible. The image formed on the liquid crystal light bulb 21 is irradiated with coherent light 23 which is split into linearly polarized light by a polarizing beam splinter 22 and whose polarization axis direction matches the director direction of the ferroelectric liquid crystal molecules at the time of total erasure. The irradiated light undergoes polarization state conversion due to birefringence and is reflected only at the portion where the director is reversed due to writing. The reflected light passes through the beam sub-soter 22 again, and the intensity of the portion where the polarization state has been changed due to birefringence is inevitably lowered, so that the polarized beam sub-soter 22 converts the incident light 23 into a liquid crystal light. It is combined with the precepts that did not enter the bulb 21, and is sent to the lens 24. Optical information processing is performed by forming an image on a correlation coordinate plane 27 through a massotid filter 25 and a lens 26. In this application example, by using an incoherent-coherent converter using the liquid crystal optical element of the present invention, a coherent optical correlation system that can be used for large objects and can perform high-speed processing close to real time is created. It will be realized. [Effects of the Invention] As described above, if the divided photoconductive layer structure of the present invention is used, there will be no DC defects and a uniform molecular arrangement will result in high contrast and a good image with sharp image edges. A high-speed, high-resolution, and highly reliable optically written ferroelectric liquid crystal light valve with memory properties can be realized, and a large-area, high-speed incoherent-coherent converter, high-speed, high-density, high-speed access, and rewrite/erasable are possible. Applications such as optical bistable memory are possible. Specifically, the scope of application to intermediate recording media of optical printers, image display devices, optical shutters, image processing devices, optical information processing systems, etc. can be dramatically expanded.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of a liquid crystal light valve according to the present invention, FIG. 2 is a schematic diagram showing a divided structure of a photoconductive layer according to the present invention, and FIG. Figure 4 shows the voltage vs. light reflectance characteristic diagram when light is irradiated by DC bias voltage driving. Figure 4 shows the voltage vs. light reflectance characteristic diagram when light is irradiated by DC bias voltage driving with an AC waveform superimposed on the optical writing type liquid light valve of the present invention. A reflectance characteristic diagram, FIG. 5 is an optical writing system diagram of an image writing device using the liquid crystal light valve of the present invention,
Figure 6 is a conceptual diagram of a coherent system using the liquid crystal light valve of the present invention. 1, 2...Transparent substrate 3.4...Transparent electrode 5.6...Liquid crystal alignment layer, +IJ dielectric liquid crystal, dielectric ξ layer, photoconductive layer, insulating layer, writing light, projection light 13b. ...Divided photoconductive layer 14b...Insulating layer...Mask...Optically written liquid crystal light valve...Measurement object 26...Lens, optically written liquid crystal light valve, beam splinter・Coherent light・Matched filter・Correlation coordinate plane・Temperature controller・PIN photo・Lamp 7 ・ ・ ・ ・ 8 ・ ・ ・ ・ 9 ・ ・ ・ 1O・ ・ ・ ・ 11・ ・ ・ ・ 12・ ・ 13a 14a, 17・ ・ 18・ ・ l9 ・ ・ 20, 24, 21 33. ・Insulation box 34. ・Polarizer 35. ・Analyzer 36. ・Objective lens 37. ・Oscilloscope 38. ・More than oscillator.

Claims (2)

[Claims] (1) A writing means using light such as a laser beam, an LED, or a halogen light, a photoconductive layer, a light reflection layer, a liquid crystal alignment layer, a liquid crystal layer, and a voltage application means are formed, and the light reflectance and the applied voltage are formed on the liquid crystal layer. In the optical writing type liquid crystal light valve using a ferroelectric liquid crystal having bistability between
An optical writing type liquid crystal light valve characterized by being divided into sizes ranging from μm^2 to 400 μm^2. (2) The optically writable liquid crystal light valve according to claim 1, wherein the photoconductive film is hydrogenated amorphous silicon having a thickness of 2 μm to 10 μm.