JP2816576B2 - Optical writing type liquid crystal light valve - Google Patents

Description

The present invention relates to an optical recording type liquid crystal light used for an intermediate recording medium of an optical printer, an image display device, an optical shutter, an image processing device, an optical information processing system, and the like. It relates to a valve.

[Summary of the Invention]

The present invention relates to an optical writable liquid light valve combining a highly sensitive photoconductive layer exhibiting high resistivity in darkness and high conductivity during light irradiation, and a dielectric mirror having appropriate conductivity and high reflectivity. It is.

As the photoconductive layer, hydrogenated amorphous silicon (α-Si: H), which is particularly stable at the temperature at which the light valve was made (up to 200 ° C), has a high resistivity in the dark, and has a high photoconductivity when irradiated with light Etc. give good properties. The light reflection layer used for the liquid crystal light valve is formed by alternately laminating Si-Ge and SiO _{2 so} that d = nλ / 4 when a predetermined wavelength λ, a refractive index n of the material and a film thickness d are satisfied. Is a dielectric mirror that reflects the Si—Ge molecular formula of Si _1-x Ge _x , where 0.03 ≦
The composition satisfies x ≦ 0.18.

By using the light valve according to the present invention, it is possible to provide a light writing type image projection device which can display a high-definition image and can display a moving image at a high writing speed.

[Conventional technology]

2. Description of the Related Art Conventionally, in research on optical information processing and optical pattern recognition, a number of optical writing type liquid crystal light valves have been studied for converting incoherent optical information into coherent optical information and for spatially modulating optical information.

In order to improve the resolution, contrast and response speed, the above-mentioned light-writing type liquid crystal light valve uses a ferroelectric liquid crystal, TN liquid crystal, SmA liquid crystal, or the like as a liquid crystal layer to be used. In the following, α-
Many attempts have been made or applied to chalcogenide compounds such as Si: H) or CdSe or organic photoconductive materials.

In particular, in the case of a reflective type optical writing liquid crystal light valve that reads out optical information, the Si / SiO ₂ multilayer mirror is used as a dielectric mirror with high reflectance and electrical characteristics suitable for the liquid crystal drive circuit parameters. It has been.

In addition, research on forming a dielectric mirror by a combination of SiO ₂ / TiO ₂ , ZnS / MgF _{2 and the} like has been attempted.

[Problems to be solved by the invention]

However, when a dielectric mirror is made of the conventional Si / SiO ₂ as described above, the resistivity in the in-plane direction is too low, and when light is applied, a voltage is applied to the entire surface, and depending on the degree, an image is formed depending on the degree. There has been a problem that the resolution cannot be increased due to blurring, unevenness, or inability to write an image.

In addition, there is a problem that the same characteristics as described above are exhibited even when a semiconductor junction between hydrogenated amorphous silicon (hereinafter referred to as α-Si: H) which is a photoconductive film and a dielectric mirror is used.

[Means for solving the problem]

The present invention to solve the above problems, in the case of manufacturing a dielectric mirror with Si / SiO _2, specific since the resistance is too low, Si-
The Ge / SiO ₂ are alternately stacked, when the Si-Ge molecular formula was Si _1-x Ge _x, by a composition of 0.03 ≦ x ≦ 0.13, to increase the specific resistance was to solve the above problems.

Further, a photoconductive layer a-Si: for eliminating semiconductor junction of H and dielectric mirror, a-Si: SiO ₂ on the H is an insulating film
Was formed, and a dielectric mirror was formed thereon to avoid the semiconductor junction between a-Si: H and Si-Ge, thereby solving the above problem.

Embodiment FIG. 1 shows a combination of a high-sensitivity photoconductive layer showing high resistivity in darkness and high conductivity in light irradiation according to the present invention, and a dielectric mirror having moderate conductivity and high reflectivity. It is sectional drawing which shows the structure of a light writing type liquid crystal light valve.

In this example, first, a transparent glass substrate was prepared as the transparent substrates 11a and 11b, and an ITO transparent electrode layer was formed on the surface as the transparent electrode layers 12a and 12b.

On the optical writing side transparent electrode layer 12a, a gas mainly composed of SiF ₄ is subjected to discharge decomposition to form intrinsic hydrogenated amorphous silicon (α-Si: H) having a heat of 3 μm. And

A light-shielding layer 16 was provided on the photoconductive layer, and 15 layers of Si and SiO ₂ were further laminated to form a dielectric mirror 17. When the visible light reflectance of the dielectric mirror is sufficiently large and the influence of the reading light on the photoconductive layer 15 is extremely small, the light shielding layer can be omitted. Silicon monoxide (Si) is placed on the dielectric mirror 17 and the projection electrode on the projection side.
O) was obliquely vapor-deposited to a thickness of 2000 ° with a film thickness meter set at an angle of 82 ° with respect to the normal direction of the substrate and in the normal direction of vapor deposition to form liquid crystal alignment layers 13a and 13b. The transparent substrates 11a and 11b face the alignment film layers 13a and 13b, and the gap is controlled and formed by a spacer 19 using an adhesive containing glass fiber with a diameter of 1.5 μm, and the ferroelectric liquid crystal layer 14 is sandwiched. I did it. The encapsulated ferroelectric liquid crystal composition is an ester-based SmC
4 ((4′-otatyl) phenyl) as a liquid crystal mixture
Benzoic acid (3 "-fluoro, 4" -octyloxy) phenyl ester and 4-((4'-octyloxy) benzoic acid (3 "-fluoro, 4" octyloxy) phenyl ester were mixed 1: 1. Using, as an optically active substance 5-octyloxynaphthalene carboxylic acid,
A ferroelectric liquid crystal composition was prepared by adding 25% by weight of 1'-cyanoethyl ester.

FIG. 2 is a configuration diagram of the dielectric mirror 17 according to the present invention. SiO ₂ was deposited on the photoconductive layer α-Si: H15 by vacuum evaporation.
This is a 15-layer structure in which a pair of 24 is about 942 ° and Si _1-x Ge _x 23 is repeated 7 times seven times, and Si _1-x Ge _x is formed thereon.

Further, SiO ₂ as an insulating layer 22 was sandwiched between α-Si: H15 as a photoconductive layer and Si _1-x Ge _x 23. Thus, α−
Due to the semiconductor junction between the Si: H15 and the dielectric mirror 17, the specific resistance ratio in the in-plane direction was too low, and it was possible to prevent voltage from being applied to the entire surface when irradiated with light. This time, SiO ₂ was used for the insulating layer, but other insulating layers such as GeO ₂ and TiO ₂ are also possible.

The light-shielding layer 16 between the photoconductive layer 15 and the dielectric mirror 17 was omitted because the visible light reflectance of the dielectric mirror was sufficiently large and the influence of the readout light was extremely small.

FIG. 3 shows the characteristic of the specific resistance with respect to the composition ratio. The specific resistance of the ferroelectric liquid crystal of the liquid crystal light valve of the present invention is 10 ¹¹ to 10 ¹² Ωcm, and the specific resistance of α-SiH is 10 ⁵ at the time of light.
Ωcm, 10 ¹⁰ -10 ¹¹ Ωcm in the dark, and the specific resistance of the dielectric mirror is 10 ⁹ -10 to drive the liquid crystal light valve.
It must be ¹⁰ Ω · cm. The horizontal axis shows the composition ratio X of Si _1-x Ge _x , and the vertical axis shows the specific resistance at the time of the composition. From the figure, it was found that when the specific resistance of the dielectric mirror was 10 ⁹ to 10 ¹⁰ Ω · cm, the composition ratio X was between 0.055 and 0.13. Therefore, in the present example, it was manufactured using a raw material having a composition ratio of X = 0.08. This time, the value of X was as described above, but the specific ratio of Si _1-x Ge _x manufactured under the manufacturing conditions fluctuated, so the range of the composition ratio was 0.03 ≦ X ≦ 0.18.

FIG. 4 shows the optical characteristics of the dielectric mirror according to the present invention. From the figure, the visible light reflectance was 90%, and the visible light transmittance was 0%. The reason why the transmittance is 0% while the reflectance is 90% is because there is light absorption of Ge. Thus, it can be seen that the visible light has a high reflectivity, has characteristics of transmitting only writing light and reflecting reading light.

When writing image information or the like to an optical writing type liquid crystal light valve according to the present invention using an LD or an LED, first, light is applied to the entire surface of the liquid crystal light valve and a DC voltage sufficiently higher than the threshold voltage is applied. Or applying a DC bias voltage that is sufficiently higher than the threshold voltage in darkness and when not irradiating light, aligns the ferroelectric liquid crystal in one-way stable state, and stores the memory in that state. I do.

Next, without performing light irradiation, a DC voltage having a reverse polarity that is equal to or lower than the threshold voltage in darkness and equal to or higher than the threshold voltage during light irradiation is applied in advance, and an optical writing unit such as a laser beam or an LED is used. The image information to be projected and displayed is written using light. Since the photoconductive layer used here has a sufficiently high sensitivity to light having a wavelength of 700 to 850 nm, for example, 780 nm
When irradiated with a semiconductor laser having a center wavelength of, the photoconductive film 15 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 and applied to the liquid crystal molecules. To excite. The region that is not irradiated with light remains at a high resistance, so that almost no voltage is applied to the liquid crystal molecules, so that the liquid crystal molecules are not excited,
As a result, the data is stored in the light irradiating portion and the non-light irradiating portion while being different in the arrangement direction of the liquid crystal molecules.

When the image information written in this way is irradiated with linearly polarized projection light that has passed through a polarizer, the image information is reflected by a reflective layer, and is projected and displayed on a screen through an analyzer. Polarizer,
Using a polarizer with a degree of polarization of 99.9% and a single transmittance of 38% for the analyzer, the Cotrast ratio between the bistable states was measured.
It showed extremely high values of 400: 1 or more. In liquid crystal display modes such as TN type and DSM type which do not have bistability and memory,
Although the amount of reflected light of the liquid crystal molecules is modulated by the voltage directly applied to the liquid crystal molecules, the image holding time is extremely short.

On the other hand, according to the present invention, the light reflectance becomes 1 or 0 because of the threshold characteristic and the bistable memory property, so that a halftone cannot be obtained. As long as no voltage is applied or strong pressure is applied, it is held semi-permanently. When the voltage was kept open after the image was formed and the measurement was performed again three days later, it was confirmed that the contrast ratio hardly changed and that the device had extremely excellent memory properties.

As the liquid crystal alignment film used in the present invention, in addition to the SiO oblique deposition film, a mixed solution of a basic chromium complex as a vertical alignment agent and a polyimide as a horizontal alignment agent is applied and baked, and then subjected to a rubbing treatment. Therefore, there is no problem even if the alignment film provides a high pretilt angle of 10 ° to 30 °.
Further, as the liquid crystal to be filled, even if a pyrimidine-based chiral smectic mixed liquid crystal composition or a liquid crystal mixture of an ester-based chiral smectic liquid crystal composition and a pyrimidine-based chiral smectic liquid crystal composition is used, the same effect is obtained. .

Next, an application example of the optical writing type liquid crystal light valve of the present invention will be described. FIG. 5 is a conceptual view of a digital color laser printer to which a light writing liquid crystal light valve using a liquid crystal optical element of the present invention is applied. In the figure, reference numerals 31a, 31b, and 31c denote liquid crystal optical elements according to the present invention. After an image corresponding to R, G, and B is written by a laser scanner 32, a filter corresponding to each color is written by a projection optical system 33. An image of each color is formed on the medium 34 with light whose wavelength is limited by using. The medium 31 is a microcapsule 50a, 50b, 50c which cures in response to light of different wavelengths as shown in FIG. 6 and encloses a leuco dye of yellow Y, cyan C, magenta M, respectively. base
A color image is formed on the receiver sheet 35 by being pressed by a pressure roller 36 onto the receiver sheet 35 to which the color former has been applied.

By applying the light-writing liquid crystal light valve according to the present invention to the above system, a digital color laser printer with high image quality and short output time can be realized.

In addition, by setting a screen at the position of the medium 34 of the digital color laser printer and simultaneously projecting three colors, a high quality color projector can be realized.

Next, a case where the liquid crystal optical element of the present invention is an incoherent / coherent converter will be described. In this case, the photoconductive layer 15 shown in FIG. 1 is formed by vacuum-depositing CdS, Se, SeTe or the like, or an organic substance, or a multi-layer of a function separation type. Other configurations are the same as those described above.

According to the incoherent / coherent converter as described above, the incoherent writing light from the outer surface of the cell
An image is formed on the ferroelectric liquid crystal layer 14 by 20, and the image formed by writing is oriented in the alignment direction of liquid crystal molecules (or a direction perpendicular thereto) that has been previously aligned by the application of electrolysis opposite to the application direction during writing. It can be read out by irradiating the coherent projection light 21 through a polarizer whose polarization axis is aligned and by projecting through an analyzer in a direction perpendicular (or parallel) to the polarization direction of the reflected light at the time of total erasure. .

Hereinafter, an example in which the liquid crystal optical element of the present invention is applied as an incoherent / coherent converter will be described.

FIG. 7 is a conceptual diagram of a coherent light correlation system using a liquid crystal optical element according to the present invention. The reflected light from the measuring object 41 is transmitted through a lens 42 to the liquid crystal optical element according to the present invention.
Here, the liquid crystal optical element according to the present invention has a larger area than that using a non-linear optical crystal, so that it can cope with a large measurement object, and D
Since the response speed is faster than that using a liquid crystal in a mode such as SM, high-speed processing near real time is possible. The image generated on the liquid crystal optical element 43 has a polarizing beam splitter.
The light is divided into linearly polarized light by 44, and the coherent light 45 whose polarization axis direction matches the director direction of the ferroelectric liquid crystal molecules at the time of all erasure is applied. Irradiation light is reflected only after conversion of the polarization state due to birefringence in a portion where the inversion of the director has occurred by writing. The reflected light passes through the polarization beam splitter 44 only in a portion that has undergone a change in the polarization state due to birefringence, passes through a lens 46, a matched filter 47, and a lens 48 to form an image on a correlation coordinate plane 49. The processing is performed. In this application example,
By using the incoherent / coherent converter using the liquid crystal optical element of the present invention, a coherent light correlation system that can be used for a large object and that can perform high-speed processing in near real time is realized.

Next, a case where the liquid crystal optical element of the present invention is an optical bistable memory will be described. In this case, the photoconductive layer of FIG.
15 is ₃ to 10 μm by subjecting a gas mainly composed of SiF ₄ to discharge decomposition.
A-Si: H layer having a thickness of Here, the photoconductive layer 15 is a film composition to which p, n, etc. are added at the time of discharge decomposition, or an n-type or p-type semiconductor film between the a-Si: H layer and the ITO transparent electrode. An organic photoconductive film formed by a laminated structure, a printing method, or the like, or a photoconductive film formed by vapor deposition of Se, SeTe, or the like may be used. The other configuration is as shown in FIG. 1 and has already been described, so that the description is omitted here.

The data written here is read light (projection light) passing through a polarizer whose polarization axis is aligned in the direction of the liquid crystal molecules (or a direction perpendicular to the direction) of the liquid crystal molecules that has been previously adjusted by applying an electric field in the opposite direction to the application direction at the time of writing. 21 and the intensity of the reflected light passing through the analyzer in a direction perpendicular (or parallel) to the polarization direction of the reflected light at the time of the total erasure can be read out.

In a memory using such a liquid crystal optical element, since the data density depends on the spot diameter of the laser beam, the CD-RO
It was confirmed that it was an optical bistable memory that could perform high-density recording equivalent to M, had a high access speed, could be erased and rewritten many times, and did not require a backup power supply.

Hereinafter, an example in which the liquid crystal optical element of the present invention is applied to an optical bistable memory will be described.

FIG. 8 is a conceptual diagram of an optical disk memory using the liquid crystal optical element of the present invention, and FIG. 9 is an enlarged view of only the central portion of the optical disk memory. The structure of the memory units 71a and 71b in FIG. 8 is the same as that of FIG. 1, and a readout optical system 73 in which a polarizer and an analyzer are added to a configuration similar to that of a CD pickup is used. The writing optical system 72 using a semiconductor laser is provided on the side where no layer is provided with the memory units 71a, 72
It was arranged on the photoconductive film side of b. Also, the optical disk memory 7
In the center of 0, as shown in FIG. 9, the transparent electrodes of the transparent electrode substrate are provided with exposed portions 81a and 81b, respectively.
The rotating shaft / electrode pads 82a and 82b are brought into contact with this portion and rotated while applying an electric field to the exposure disk memory.
The scanning is performed by the rotation and writing optical system 72 and the reading optical system.
This is performed by moving the disk 73 in the radial direction.

In the optical disc memory of this application example, since the data density depends on the spot diameter of the laser beam, high-density recording equivalent to a CD-ROM can be performed, and the access speed is high.
It was confirmed that it was an optical bistable memory that could be erased and rewritten any number of times and did not require a backup power supply.

Further, unlike the above, the optical memory is manufactured in a card type shape, and writing is performed by an optical system using a polygon mirror or a galvano mirror, or an LED array. quickly,
In addition, it was confirmed that the optical bistable memory can be erased and rewritten many times and does not require a backup power supply.

〔The invention's effect〕

As described above, according to the liquid crystal optical element of the present invention, the contrast ratio is large, the response speed is high, high-speed writing with a laser beam or the like is possible, and the liquid crystal light valve with high resolution can be manufactured by a simple process and the resolution is high. , Large-area, high-speed incoherent-coherent converter and large contrast ratio, addressing with light such as laser in a short time, high-density high-speed access, erasing / rewriting possible, and no backup power supply required An optical bistable memory can be realized only by changing the photoconductive layer, so that an intermediate recording medium of an optical printer, an image display device, an optical shutter,
It significantly increases the performance and application range of coherent correlation systems, other image processing devices, optical information systems, and the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light-writing type liquid crystal light valve of the present invention, FIG. 2 is a configuration diagram of a dielectric mirror according to the present invention, and FIG. 3 is a diagram showing characteristics of specific resistance with respect to a composition ratio of Si and Ge. ,
FIG. 4 is a view showing the optical characteristics of the dielectric mirror according to the present invention, FIG. 5 is a schematic view of a digital color laser printer to which the optical writing type liquid crystal light valve of the present invention is applied, and FIG. 6 is a digital color laser printer. FIG. 7 is a conceptual diagram of a coherent correlation system using an optical writing type liquid crystal light valve of the present invention, and FIG. 8 is an optical disc memory using an optical writing type liquid crystal light valve of the present invention. FIG. 9 is a diagram for explaining the operation of an optical disk using the optical writing type liquid crystal light valve of the present invention. 11a, 11b: Transparent substrate 12a, 12b: Transparent electrode layer 13a, 13b: Alignment layer 14: Ferroelectric liquid crystal layer 15: Photoconductive layer 16: Light shielding layer 17: Dielectric mirror 18 … Non-reflective coating layer 19… Spacer, adhesive 20… Write light 21… Read light 22… Insulating layer 23… Si _1-x Ge _x 24… SiO ₂ 31a, 32b, 31c… Liquid crystal light Bulb 32 Laser scanner 33 Projection optical system 34 Write media 35 Receiver sheet

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/135 G02F 1/1335

Claims (3)

(57) [Claims] 1. A light writing type liquid crystal light valve having a writing means using light such as a laser beam or an LED, and a photoconductive layer, a light reflecting layer, a liquid crystal alignment layer, a liquid crystal layer, and a voltage applying means. Si-Ge and SiO ₂ whose layers are mixed crystals of Si and Ge
A light-writing type liquid crystal light valve, which is a dielectric mirror in which are alternately stacked. Wherein when the Si-Ge of the dielectric mirror of the light reflecting layer used in the liquid crystal light valve is its molecular formula as Si _1-x Ge _x, characterized in that it is a composition of 0.03 ≦ x ≦ 0.18 The light-writing type liquid crystal light valve according to claim 1. 3. A dielectric mirror for use in the liquid crystal light valve has a predetermined wavelength λ, a refractive index n of a material, and a film thickness d on a photoconductive layer. _2. The light-writing type liquid crystal light valve according to claim 1, wherein _two films are alternately laminated to reflect visible light.