JPH01315723A - Optical writing type liquid crystal light valve - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal light value with high resolution by employing, as a liquid crystal layer, a ferroelectric liquid crystal having a threshold characteristic and a bistable memory between light reflectance and an impressed voltage. CONSTITUTION:A transparent electrode 3a, photoconductive film 4, light-shielding film 5, light reflecting film 6, and liquid crystal orientation film 7a are formed inside a transparent substrate 2a on the side where an image is written by using an optical writing means 1 such as laser beam, LED, CRT, etc.. In such an optical writing liquid crystal value, a photoconductive layer is sensitive to the light having 700-850nm wavelength; therefore an image is written by using the optical writing means 1, for example, a semiconductor laser having 780nm central wavelength, after a first processing where d.c. bias voltage far higher than a threshold value voltage is impressed in order to obtain one direction stability. Then, by irradiating the light of a 500W halogen lamp from the projecting side and then projecting the image onto a screen 12 through a polarizer and analyser, a projected image with a high contrast can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical writing type liquid crystal light valve used in high-definition image display devices, printers, and the like.

[Summary of the invention]

The present invention provides an optically writable liquid crystal light valve in which a ferroelectric liquid crystal having threshold characteristics and bistable memory properties is used in the liquid crystal layer, and a DC bias voltage sufficiently larger than the threshold voltage of the liquid crystal light valve is applied. By keeping the directors of liquid crystal molecules uniformly aligned on the entire surface! After going through the process of
The second step is to write an image using light irradiation from a laser beam or LED while applying a DC voltage that is opposite in polarity to the first step and is below the threshold voltage when it is dark and below the threshold voltage when irradiated with light. By adopting this method, it is possible to provide an extremely high-speed, high-definition optical writing type liquid crystal light valve that can write and hold image information with one high-speed beam scan.

By using the light valve according to the present invention, it is possible to provide an optical writing type image projection device that can display high-definition images, has a fast writing speed, and can display moving images. Also, I
? -G- It is also possible to realize a full-color image projection device by preparing a liquid crystal light valve for writing images of 83 colors and projecting and combining the three-color images onto a screen after writing.

[Conventional technology]

Conventionally, optical writing type liquid crystal light valves have used various addressing methods and display modes of the liquid crystal used. Addressing methods include an optical writing type that combines liquid crystal and a photoconductive film, a thermal writing type using laser light, etc. Display modes of liquid crystal include SmA phase transition, Ne -ch phase transition, DSM, TN, STN, etc. is used. In particular, the optical writing type has a faster recessing speed than the thermal writing type, and is expected to be applied to video displays and the like.

[Ll'a to be solved by the invention] However, in the conventional technology as described above, the liquid crystal layer produces an electro-optic effect only when irradiated with light, and when the irradiation of light ends, the formed image disappears. Liquid crystal time constant C1? Therefore, it will be retained for only a short time and then disappear. - In an optical writing type liquid crystal light bulb using a 90° twisted nematic type liquid crystal, the light source mainly uses Cr, which has the afterglow effect of the phosphor. T, etc. were used, but in this case the resolution of the light valve was approximately C.
I? This has disadvantages such as high cost and an increase in the size of the device.

In contrast, writing by laser beam scanning has been devised, but in this case, the image can be retained for a short time, so the resolution cannot be increased, and when trying to obtain a high resolution large screen display, It is necessary to repeat multiple Gs at the same exact location at high speed, and this requires the development of an ultra-high-speed, ultra-reliable laser scanner and an ultra-sensitive photoconductive film. Many problems were piling up.

[Means to solve the problem]

The present invention uses a bistable memory ferroelectric liquid crystal that has a threshold characteristic between light transmittance or light reflectance and applied voltage as an optically writable liquid crystal light valve.

[Effect]

According to the present invention, the entire surface of the light valve is irradiated with light, and a DC bias voltage that is sufficiently higher than the threshold voltage in the bright state is applied to align the ferroelectric liquid crystal to a stable state in one direction and to memorize that state. Alternatively, without light irradiation, a DC bias voltage sufficiently higher than the threshold voltage at 09:00 is applied to align the ferroelectric liquid crystal to a stable state in one direction, and the state is memorized. After such a first step, without light irradiation,
It is below the threshold voltage in the dark, and below the threshold voltage for light irradiation.
A second step of optical writing using a laser beam or the like is performed while applying a DC bias voltage of opposite polarity.
As a result, carriers are generated in the photosensitive layer in the area exposed to light irradiation, 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 light irradiation is performed. A bias voltage of opposite polarity equal to or higher than the threshold voltage is applied to the region, and the molecules are inverted as the spontaneous polarization is reversed, and the region is memorized in the other stable state. The image formed in this way is based on the irradiation of linearly polarized projection light whose polarization axis is aligned with the direction of the C director aligned in the first step (or in the direction perpendicular to it), and the polarization direction of the light reflected by the reflective layer. On the other hand, it can be read out on a screen by projection through an analyzer arranged so that the polarization axes are perpendicular (or parallel).

In addition, after the second step is completed, partial erasure (partial erasure) is achieved by inverting the plum color again and performing light irradiation while applying a DC bias voltage that is less than the threshold voltage in the dark and more than the threshold voltage in the light. 4 speed) can also be performed.

[Example] FIG. 1 is a sectional view showing the structure of a liquid crystal light valve according to the present invention. The structure of Ly-Pulp is different from conventional examples in that the liquid crystal layer uses a bistable memory ferroelectric liquid crystal that has clear threshold characteristics between the optical I3 pass rate or optical reflectance and the applied voltage. It's true. The present invention will be explained below using figures.

A transparent electrode 3a + a photoconductive film 4. Light-shielding M45° light-reflecting film 6. A liquid crystal alignment film 7a is formed, and a counter transparent electrode 3 is provided inside the transparent substrate 2b on the side reflected and projected by the projection light 8.
b, a liquid crystal alignment film 7b is formed. These pair of transparent substrates are overlapped by a peripheral seal 9 containing a spacer material such as glass fiber, and a ferroelectric liquid crystal 10 is sealed in the gap between them. By applying an appropriate bias voltage between the two transparent electrodes 3a and 3b of the liquid crystal light valve formed in this manner, the image information to be projected and displayed can be oldened with light using an optical writing means such as a laser beam or LED. The photoconductive film 4 that has been irradiated with light generates carriers and enters a low resistance state, and the applied bias voltage is applied to the liquid crystal layer in a resistance-divided form to excite liquid crystal molecules. The region that is not irradiated with light retains a high resistance, so almost no voltage is applied to the liquid crystal molecules, and the liquid crystal molecules are not excited, making T a non-bistable and non-memory T.
In liquid crystal display modes such as N type and DSM type, the amount of reflected light between liquid crystal molecules is modulated by a voltage directly applied to the liquid crystal molecules, but the image retention time is extremely short.

On the other hand, according to the present invention, the light reflectance cannot take halftones due to its threshold characteristic and bistable memory property, and 1 becomes 0. Otherwise, unless strong pressure is applied, it will be maintained semi-permanently. When the image written in this way is irradiated with the projection light 8, the image reflected by the reflective film 6 will be projected and displayed on the screen 12.

In the present invention having the above configuration, the transparent glass substrate 2'a,
As 2b, for example, Corning! Prepare IJ7059 glass and place ■T on the surface as transparent electrodes 3a and 3b.
The Oi3 bright electrode was used as a shaped electrode. A photoconductive film 4° dielectric mirror 6 was laminated on the ITO transparent electrode 3a on the writing side by the laser beam 1. The photoconductive layer 4 is a functional component 1 ((() type organic photoconductor having a charge generation layer and a charge transfer layer. .5ffifilt part and saturated polyester resin (Toyobo Vylon 200) 0.
The 4-layer ■ part was mixed with tetrahydrofuran in a ball mill for 6 minutes.
After kneading for a while, dry it with an applicator (manufactured by Toyo Soki Co., Ltd.) and then use it! A charge generation layer was prepared by coating in a thickness of 2 and 1. Next, P-dimethylaminobenzaldehyde-1゜1゜diphenylhydrazone 0.1 manufactured by Anan Perfumery Co., Ltd.
5g to polycarbonate (Kijin Panlite) 0.3g
In addition, 3 ■ dichloromethane, 1.2 l dichloroethane
After mixing with the mixed solvent of (2), perform ultrasonic dispersion for 20 minutes, and use an applicator to apply the dried film onto the charge generation layer.
A charge transfer layer was prepared by coating to a thickness of 5jIm. On the charge transport layer, thin films of MgF and ZnS are deposited alternately.
After forming the light reflecting film 6 by depositing and laminating the NN, silicon monoxide was deposited at an angle of 80° to the normal direction of the glass substrate to a thickness of 2000 mm using a film thickness meter to align the liquid crystal [7! 1 was formed. Similarly, a silicon monoxide liquid crystal orientation 1127b is formed on the ITO33 bright electrode 3b of the other transparent electrode 2b,
These two substrates were arranged so that the liquid crystal alignment films 7a and 7b faced each other, and the ferroelectric liquid crystal 10 was sandwiched between the outer peripheral seal 9 and the 1.5 pm silica ball spacer.
The ferroelectric liquid crystal composition used in this example is a ferroelectric liquid crystal composition obtained by adding an optically active substance to an ester-based SmC liquid crystal mixture. ) Benzoic acid (3”-fluoro, 4m-octyloxy)phenyl and 4-((4'-octyloxy)phenyl)benzoic acid # (3”-fluoro, 4m-octyloxy) were mixed in taX. and 5-octyloxynafcrenecarvone M, as an optically active substance.
1'-Also, an anti-reflection coating [11] may be formed on the projection light irradiation side of the glass substrate 2b on the projection side by vapor deposition of MgF.

Since the photoconductive layer of the optically writable liquid crystal light valve produced as described above is sensitive to light with a wavelength of 700 to 850 nm, it can be stabilized in one direction by applying a DC bias voltage that is sufficiently larger than the threshold voltage. After going through the first step of adjusting the state, image reading is performed with writing light 1 using, for example, a semiconductor laser with a center wavelength of 780 nm. After this, a 500 W/W halogen lamp is turned on from the projection side. irradiated and projected onto the screen 12 through a polarizer and an analyzer,
A high contrast projection image was obtained.

Further, as the photoconductive film 4, Si is coated on the ITO transparent electrode 3a.
Discharge decomposition of gas mainly consisting of F4 to produce 1μI of a-s+
After forming -Hjffl, its a -S+ -II
When 11,000 PP of Pll was mixed with SiF4 gas and subjected to discharge decomposition to form 1,000 nplJ on the layer, similar decomposition and projection were performed, and an extremely clear and high contrast projected image was obtained. I was able to get it.

Furthermore, a piece of a-Si formed by discharging and decomposing the ITO transparent electrode 3a and a gas mainly composed of SiF4:
H light 1fflW! Between J4 and S i Fa, 1:
13! A similar projection image was obtained by mixing 11,000 pp of +14 and performing discharge decomposition to form 1,000 pPJs.

In addition to the SiO oblique vapor deposition film, the liquid crystal alignment film used in the present invention is coated with a mixed solution of basic chromium chains as a vertical alignment agent and polyimide as a horizontal alignment agent, and then subjected to rubbing treatment. There is no problem even if the alignment film is applied to give a high pretilt angle of 20° to 40''.Also, the liquid crystal to be encapsulated may be a pyrimidine-based chiral smectane liquid crystal composition or an ester-based chiral liquid crystal composition. Exactly the same effect has been obtained using a liquid crystal mixture of a smectic liquid crystal composition and a pyrimidine-based chiral smectic liquid crystal composition.

FIG. 2 shows voltage-light reflectance characteristics when the liquid crystal light valve according to the example was used and a voltage was applied between the electrodes while irradiating the entire surface with light from the aged side. In this case, the photosensitive layer is in a conductive state (low resistance state a) over the entire surface.
Therefore, the applied voltage is applied to the ferroelectric liquid crystal layer with almost no loss. The voltage waveform is 0.111z,
As is clear from FIG. 8 using a 20 Vp-p triangular wave, the liquid crystal light valve according to the present invention exhibits clear threshold characteristics and large bistability.

In addition, the polarizer and analyzer have a polarization degree of 99.9% and a single transmittance of 3.
When we measured the contrast ratio between the bistable states using an 8% Royal polarizing plate, it was over 400:1, and the voltage was almost the same! When the contrast ratio was measured again after 3 days, it was found that there was almost no change in the contrast ratio and that it had excellent memory properties. It was done.

Next, the application of the optical writing type liquid crystal light valve according to the present invention will be explained using an example.

FIG. 3 is a conceptual diagram of a digital color laser printer to which the optical writing type liquid crystal light valve according to the present invention is applied.
In the figure, an optical writing type liquid crystal light valve 31a according to the present invention,
31b and 31c are each scanned by a laser scanner 32,
After the images corresponding to R, G, and B are written, images of the respective colors are formed on the medium 34 by the projection optical system 33 using light whose wavelengths are limited using filters corresponding to the respective colors.

The medium 34 includes microcapsules 40 that harden in response to light of different wavelengths, as shown in FIG.
a, 40b, and 40c, leuco dye encapsulated therein is dispersed and coated on the base 41, and by pressing it against the receiver sheet 35 coated with a coloring agent,
A color image is formed on a receiver sheet. By applying the optical writing type liquid crystal light valve according to the present invention to the above-mentioned system, it was possible to realize an excellent digital color blink that can output high-quality images in a short time.

Moreover, the media 3 of the digital color laser printer
By placing the screen at position 4 and projecting three colors simultaneously, we were able to create a color projector with high quality and high speed response.

Next, a case where the liquid crystal optical element of the present invention is used as an incoherent-coherent converter will be described.

An image is formed on the ferroelectric liquid crystal layer 14 by incoherent writing light 20 from the outer surface of the cell, and the image formed by interpolation is aligned with the C director by applying an electric field in the opposite direction to the direction of application during writing. Irradiation of coherent projection light 21 through a polarizer with its polarization axis aligned in the direction of It can be read out by projection through.

An example of applying the liquid crystal optical element of the present invention as an incoherent-coherent converter will be described below.

FIG. 5 is a conceptual diagram of a coherent optical correlation system using a liquid crystal optical element according to the present invention. The reflected light from the measurement object 50 is imaged by the lens 42 onto the liquid crystal optical element 43 according to the present invention. Here, since the liquid crystal optical element according to the present invention has a larger area than one using a nonlinear optical crystal, it can be used even if the object to be measured is large, and
Since the response speed is faster than that using liquid crystal in modes such as TN and DSM, high-speed processing close to real time is possible. The image formed on the liquid crystal optical element 43 is irradiated with coherent light 45 that is split into linearly polarized light by a polarizing beam splinter 44 and whose polarization axis direction matches the director direction of the ferroelectric liquid crystal molecules at the time of complete erasure. The irradiation light is
Only in the portion where the director is reversed due to writing, the polarization state is changed due to birefringence and the light is reflected. The reflected light passes through the polarizing beam splitter 44 again,
The intensity of the portion whose polarization state has been changed due to birefringence is inevitably lowered, and it is combined with the component of the incident light 45 that did not enter the liquid crystal optical element 43 by the polarizing beam splitter 44, and is combined with the component of the incident light 45 that did not enter the liquid crystal optical element 43. In this application example, in which optical information processing is performed by forming an image on a correlation coordinate plane 49 through a matched filter 47 and a lens 48, incoherent-coherent conversion by the liquid crystal optical element of the present invention is performed. By using this device, we can realize a coherent optical correlation system that can be used for large objects and can perform high-speed processing close to real time.

In addition, the optical writing type liquid crystal light valve according to the present invention can be applied to various image display devices, image processing devices, and optical information processing devices.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a liquid crystal light valve with a high contrast ratio, a fast response speed, high-speed writing with laser light, etc., and a high resolution, which can be used as an intermediate recording medium for optical printers. , the performance and range of applications of image display devices, optical shunters, other image processing devices, optical information systems, etc. will be dramatically increased.

[Brief explanation of the drawing]

Figure 1 shows a cross section (2
), FIG.
3 is a conceptual diagram of a digital laser color printer to which the optical writing type liquid crystal light valve of the present invention is applied; FIG. 4 is a conceptual diagram of the media used in the digital laser color printer; FIG. 5 is a conceptual diagram of a coherent correlation system using the liquid crystal optical element of the present invention. l...Old light 2a, 2b...Transparent substrate 3a, 3b...Transparent type, pole 4...
Photoconductive layer 5... Light shielding layer 6... Dielectric mirrors 7a, 7b... Liquid crystal alignment layer 8... Projection light 9... Adhesive Spacer lO... Ferroelectric liquid crystal 11... Anti-reflection film 12... Screens 31a, 31b, 31c... Liquid crystal light valve 32...
... Laser scanner 33 ... Projection optical system 34 ... Writing medium 35 ... Receiver sheet

Claims (2)

[Claims] (1) In an optical writing type liquid crystal light valve in which a writing means by light, a photoconductive layer, a light reflection layer, a liquid crystal alignment layer, a liquid crystal layer, and a voltage application means are formed, the liquid crystal layer has a light reflectance and an application voltage. An optically writable liquid crystal light valve characterized by being a ferroelectric liquid crystal having threshold characteristics and bistable memory properties between voltages. (2) In the liquid crystal light valve according to claim 1, the first step of applying a DC bias voltage sufficiently larger than a threshold voltage to maintain alignment of liquid crystal molecules and the first step have opposite polarity. In addition, it is driven by a second step in which an image is formed by irradiating light from a laser beam, LED, etc. while applying a DC bias voltage that is below the threshold voltage when it is dark and above the threshold voltage when irradiated with light. A method for driving an optical writing type liquid crystal light valve, which is characterized by: