JPH0453406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to color thermal writing liquid crystal light valves.

(Prior Art) In recent years, there has been a demand for displays that are highly accurate and allow partial additions to images for computer-based image processing, newspaper editing, and LSI design. As a display device with a high resolution of 2000 lines or more, there is a display that performs thermal writing using liquid crystal laser light.
For example, the magazine ``Proceeding of the SID''
1978, pp. 1-7, ``Laser Selected Liquid Crystal Projection Display (LASER-ADDRESSED)''
LIQUID CRYSTAL PROJECTION
DISPLAY)”.

According to this paper, an image can be recorded by scanning with a laser beam 60 on a liquid crystal light valve 69 as shown in FIG. 6, and the image can be displayed by making projection light 61 incident and reflected. The liquid crystal light valve 69 includes a light absorption film 63 and an aluminum reflection film 6.
4. Glass substrate 62 with liquid crystal alignment film 68 formed thereon
It has a structure in which a liquid crystal material is sandwiched between a transparent electrode film 66 and a glass substrate 67 on which a liquid crystal alignment film 68 is formed. When the laser light 60 enters the liquid crystal light valve 69, the laser light 60 is absorbed by the light absorption film 63 and converted into heat, which is transmitted through the aluminum reflection film 64 and the liquid crystal alignment film 68 to increase the temperature of the liquid crystal material 65. Smectic liquid crystal is used as the liquid crystal material 65, and the smectic liquid crystal changes into a nematic phase and a liquid phase by increasing the temperature, and when the laser beam 60 is removed, it is rapidly cooled and changes to a liquid state. The random alignment state of the liquid crystal molecules is frozen, and the scattered light is read out by the projection light 61 and displayed as pixels on the screen.

Since a thermal writing liquid crystal display uses scattering and non-scattering of liquid crystal, the display is a black and white pattern. A method for displaying at least three colors is described in Japanese Patent Application No. 121036/1983 entitled "Color Thermal Writing Liquid Crystal Projection Display and Writing Method". According to the above invention, the liquid crystal light valve has three types of color filters each consisting of a diffraction grating that provides an optical phase difference so as to diffract visible light in a specific wavelength range in the zero-order direction, which are periodically arranged in a plane. It has a built-in three-color stripe color filter, which can be formed with extremely fine widths and has excellent light resistance and heat resistance. In addition, when the laser beam is scanned with a light intensity below the threshold for writing into the liquid crystal light valve and the first-order diffracted light that is reflected and diffracted from the diffraction grating in the liquid crystal light valve is received, the first-order diffracted light is passed through three types of color filters. Due to the different diffraction efficiencies of the corresponding diffraction gratings,
The intensity is modulated in a one-to-one correspondence between the scanning position of the laser beam and the position of the color filter, and the signal from a specific color filter, which is used as a reference for the position, is extracted from the electrical signal obtained from the photoreceiver. Assuming that is the writing position reference clock signal, writing to each color filter position is done by providing a suitable delay time from the position reference clock signal and giving the laser beam a sufficient amount of light to write to the liquid crystal light valve. Each pixel can be written with high positional accuracy.

(Problem to be solved by the invention) However, since the first-order diffracted light that has undergone intensity modulation in one-to-one correspondence with the color filter position is absorbed by the light absorption film, the electrical signal obtained by receiving the light is extremely It is weak. Furthermore, the intensity modulation of the first-order diffracted light due to the difference in diffraction efficiency has a small modulation amplitude.
In order to always extract the light reception signal from the filter of a specific color regardless of changes in the amount of writing light, a gate circuit is required, making signal processing complicated.

In addition, a color filter consisting of a diffraction grating is
The transmittance or reflectance of the projected light is theoretically determined by the amount of optical phase difference depending on the depth of the diffraction grating, so three types of color filters are used, for example, red, green,
When configured with blue, sufficient colors may not appear on the projection screen depending on the color temperature of the projection light source.

An object of the present invention is to be able to receive the first-order diffracted light from a specific color filter and the first-order diffracted light from other color filters separately, to obtain a position-based clock signal with a large modulation amplitude, and to control the writing position. An object of the present invention is to provide a color thermal writing liquid crystal light valve that is easy to process signals and can project a screen with good chromaticity.

(Means for Solving the Problems) The color thermal writing liquid crystal light valve of the present invention has the following features:
It consists of a writing-side base in which a light-absorbing film, a light-reflecting film, and a liquid crystal alignment film are sequentially laminated on a transparent base, a projection-side base in which a transparent electrode film and a liquid crystal alignment film are successively laminated on a transparent base, and a liquid crystal; The writing side substrate has a structure in which a liquid crystal is sandwiched between liquid alignment films on the surfaces of the writing side substrate and the projection side substrate, and a diffraction grating that gives at least two or more types of optical phase difference to the writing side substrate is periodically arranged in the plane. In the color thermal writing liquid crystal light valve, the color thermal writing liquid crystal light valve is provided with a light receiver that receives the diffracted light of the writing light reflected and diffracted by the diffraction grating and generates a clock signal. At least one type of diffraction grating to be provided is a diffraction grating having a plurality of groove directions two-dimensionally, and a specific one of the at least one type of diffraction grating having a plurality of groove directions two-dimensionally. The diffraction grating has one groove direction different from that of other diffraction gratings, and is formed at a depth such that high diffraction efficiency can be obtained for the wavelength of the writing light, and The light receiver is characterized in that it is disposed at a position where it receives only the diffracted light that is reflected and diffracted by the diffraction grating formed at a depth that allows the high diffraction efficiency to be obtained.

(Principle and operation of the invention) A multi-color filter, in which at least two types of color filters each consisting of a diffraction grating with an optical phase difference are arranged periodically in a plane, filters only visible light in a specific wavelength region of the projected light. In addition to having the effect of diffracting and displaying color on the projection screen, by scanning the writing laser beam with a light intensity below the threshold for writing on the liquid crystal light valve and receiving the diffracted light, the color filter and the writing light The mutual positional relationship can be known and writing can be performed with high positional accuracy. Here, if at least one type of diffraction grating used as a position reference among the diffraction gratings of the multicolor filter is formed to have multiple groove directions, the amount of light below the threshold for writing the writing laser beam into the liquid crystal light valve. When scanning with The electrical signal generated has a larger modulation amplitude than the conventional example, and moreover, a signal from a filter of a specific color that is used as a position reference can always be obtained regardless of changes in the amount of writing light. In addition, the depth of a diffraction grating with multiple groove directions used as a position reference can be formed by changing the depth for each different groove direction. It is also possible to select the depth of the grating so that the reflected first-order diffraction light efficiency, which is determined by the depth of can obtain diffracted light. By setting an appropriate delay time from the position-based clock signal obtained in this way and giving sufficient light intensity to the laser beam to write on the liquid crystal light valve, pixels are written at the position of each color filter with high positional accuracy. becomes possible.

FIG. 7 is a diagram showing the principle of a color filter using a diffraction grating used in the present invention. In FIG. 7, a glass substrate 70 with rectangular irregularities of depth a
There is a reflection type diffraction grating whose surface is coated with a light reflection film 71, and when white light 72 is incident on this, 0th-order diffraction light 73, +1st-order diffraction light 74, -1
The next diffracted light 74 is diffracted. +1st order diffraction 74, -1
The next diffracted light 75 is diffracted in different directions depending on the wavelength λ, and the diffraction direction depends on the pitch of the diffraction grating. The wavelength distribution T(λ) of the 0th order diffracted light 73 returning in the specular reflection direction depends on the depth a of the diffraction grating. If the refractive index of the medium through which the light travels is n, then the wavelength distribution T(λ) of the 0th order diffracted light of the reflection type diffraction grating is obtained by the following equation.

T(λ)=cos ² (2πna/λ) (1) In Figure 8, the refractive index n is 1.5, and the refractive index of liquid crystal is 1.5.
The value of the depth a of the diffraction grating is (a) 290 nm, (b) 520 nm,
(c) Shows the wavelength distribution of 0th-order diffracted light at 240 nm.
The colors obtained in each case are (a) blue, (b) green, and (c) red.

FIG. 3 is a perspective view of a diffraction grating with two types of groove directions. The wavelength distributions T ₁ (λ) and T ₂ (λ) of the 0th-order diffracted light of the diffraction grating with depth a ₁ and groove direction G ₁ and the diffraction grating with depth a ₂ and groove direction G ₂ are obtained from equation (1). It is shown by the following formula.

T ₁ (λ)=cos ² (2πna ₁ /λ) (2) T ₂ (λ)=cos ² (2πna ₂ /λ) (3) These two types of diffraction gratings are arranged so that the groove direction is The wavelength distribution T _S (λ) of the zero-order light when they are formed by overlapping orthogonally is obtained by the following equation.

T _S (λ)=T ₁ (λ)・T ₂ (λ) (4) (Example) FIG. 2 is a diagram showing an example of a multicolor filter used in a color thermal writing liquid crystal light valve according to the present invention. . The multicolor filter is composed of three colors: blue 21, red 22, and green 23.
Blue 21 and green 23 filters are from the groove direction G ₁ 24 from the diffraction grating, red 22 is from the groove direction G ₁
24 and a groove direction G ₂ 25 perpendicular thereto. If the medium that provides the optical phase difference is a liquid crystal with a refractive index of 1.5, the depth of the diffraction grating is blue 21.
290nm, green 23 is 520nm, red 22 is 240nm.
It is 410nm. The grating constant of the diffraction grating is 2 μm, and one pixel is formed with a size of 10 μm×30 μm. Therefore, red, green, and blue filters each having 1000 x 1000 pixels can be arranged on a 30 mm square board. Here, all the lattice constants of the diffraction gratings are made equal, but it is possible to change the lattice constants of gratings with different groove directions, etc.
It is not necessarily necessary to make all lattice constants equal.

To engrave the diffraction grating shown in Figure 2 on a substrate, here a glass substrate, first, the diffraction grating of one type of color filter is etched to a certain depth by chemical etching, ion milling, etc. on the substrate masked with photoresist. The groove can be formed by changing the position, depth, and direction of the groove, and repeating this procedure.
In addition, a similar multicolor filter can be obtained by forming a diffraction grating by patterning a photosensitive resin, or by taking a mold replica from a once-formed diffraction grating and transferring it to plastic resin.

Among the above forming methods, the characteristics of a multicolor filter obtained by transferring it to an acrylic resin using a mold will be described below. In the filter shown in red 22 in Figure 2, the chromaticity of the color filter and the diffraction efficiency of the first-order diffracted light can be increased by superimposing the diffraction grating in the groove direction _{G 2 25} on the diffraction grating in the groove direction G 1 24. did it. When a standard C light source is used as the projection light source, the chromaticity coordinates of the red 22 filter are depth
240nm, groove direction G ₁ Diffraction grating with only 24 X =
0.49, Y=0.37, but with a depth of 410 nm,
Groove direction G ₂ When 25 diffraction gratings are superimposed
= 0.53 and Y = 0.35, resulting in an approximately 15% improvement in chromaticity gamut area. In addition, the diffraction grating with a depth of 410 nm and a groove direction of G ₂ 25 has a wavelength of the writing laser beam.
A first-order diffraction efficiency of 40% was obtained for 0.83 μm. In addition, for example, if a diffraction grating with a depth of 343 nm and a groove direction of G ₂ 25 is superimposed on a green 23 diffraction grating, the chromaticity gamut area will improve by 25%, and the first-order diffraction light efficiency of the writing light will increase by 24%. can get. As described above, by forming a diffraction grating in a filter of a specific color so as to have a plurality of groove directions, a multicolor filter with good chromaticity and high first-order diffraction efficiency of writing light can be realized.

FIG. 1 is a perspective view of one embodiment of a color thermal writing liquid crystal light valve according to the present invention. The color thermal writing liquid crystal light valve 1 differs from the liquid crystal light valve shown in FIG. 6 in that a diffraction grating 5 shown in FIG. 2 is engraved on a glass substrate 4 with two writing laser beams. As a light absorption film 6 on a glass substrate 4
A - group compound semiconductor film containing Cd, a - group compound semiconductor film including Te, a dye absorbing film, and a dielectric multi-interference film are formed by vapor deposition, and then A as a reflective film 7.
A film is deposited, and a polymer film, an obliquely deposited SiO film, or the like is formed thereon as a liquid crystal alignment film 8. Further, an ITO (indium tein oxide) film is attached to the other substrate 11 as a transparent electrode film 10, and is further formed into a liquid crystal alignment film 8. As the liquid crystal 9, a smectic liquid crystal such as OCBP (octyl cyano biphenyls), DCBP (decyl cyano biphenyls), or a mixture thereof can be used.

Writing in the color thermal writing liquid crystal light valve 1 constructed in this manner is performed by irradiating the laser beam 2 in the same manner as in the prior art. For example, when red, green, and blue color filters are used to generate a color image, a red image can be obtained by writing with a laser beam on the liquid crystal portions corresponding to the green and blue color filters. To obtain green and blue images, similarly, laser light can be used to write on the liquid crystal portions corresponding to the red and blue and red and green color filters, respectively. Yellow, purple, and blue-green colors are obtained by additive color mixing. Furthermore, full-color images can be realized by controlling the amount of laser light for writing and adding gradation.

In order to select the position of each color filter regardless of the non-linearity of the optical scanning writing optical system and write on the liquid crystal 9 by irradiating the laser beam 2, it is necessary to know the positional relationship between the laser beam 2 and each color filter. be. For this purpose, the laser beam 2 scans with a constant light amount below the threshold value for writing into the liquid crystal light valve 1 during the horizontal scanning period by the optical deflector 3. Laser light 2 corresponds to blue and green filters. When scanning on a diffraction grating, +1st order diffracted light 12 and -1st order diffracted light 13 shown by broken lines are reflected and diffracted, and when scanning on a diffraction grating corresponding to the red filter, +1st order diffracted light 14 in a different direction shown by dotted lines , -1st-order diffracted light 15 is also reflected and diffracted. In this way, the ±1st-order diffracted lights 14 and 15 from the diffraction grating corresponding to the red filter have different diffraction directions from the other ±1st-order diffracted lights 12 and 13, and the light receiver 1
6, the light can be separated and received. However, it is sufficient to receive at least one of the ±1st-order diffracted lights 14 and 15. The electrical signal obtained from the receiver is laser beam 2
Since this is obtained only when scanning the red color filter which is used as a position reference, this can be used as a position reference clock signal. When writing to the position of each color filter, when there are red, green, and blue image signals, set an appropriate delay time from the position reference clock signal, and send the laser beam with sufficient light intensity to write to the liquid crystal light valve. It is done by giving.

FIGS. 4 1, 2, and 3 are diagrams showing examples of electrical signals obtained by receiving the first-order diffracted light of the writing light. Compared to the conventional examples shown in FIGS. 1, 2, and 3, it was possible to obtain a writing position control clock signal with a large modulation amplitude regardless of changes in the amount of writing light without using a gate circuit.

(Effects of the Invention) As described in detail above, in this invention, the clock signal for writing position control can always be obtained from a specific filter with the position reference regardless of changes in the amount of writing light, so that each pixel can be accurately can be written at the position of the color filter, and has the effect of improving the chromaticity of the color filter.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a color thermal writing liquid crystal light valve according to the present invention, FIG. 2 is a diagram showing an embodiment of a multicolor filter used in the color thermal writing liquid crystal light valve according to the present invention, and FIG. is a perspective view of a diffraction grating with a plurality of groove directions used in the present invention, FIG. 4 is a diagram showing a photodetector signal obtained by the present invention, FIG. 5 is a diagram showing a conventional photodetector signal, and FIG. 6 is a diagram showing a conventional photodetector signal. 8 and 7 are cross-sectional views showing a conventional liquid crystal light valve, and are diagrams showing the principle of wavelength selection of a diffraction grating used in the present invention. In the figure, 1: color thermal writing liquid crystal light valve, 2: laser beam, 3: optical deflector, 5: diffraction grating, 12, 14: +1st order diffracted light, 13, 15: -
1st-order diffracted light, 16: photoreceiver, respectively.

Claims (1)

[Claims] 1 Consists of a writing side base in which a light absorption film, a light reflection film, and a liquid crystal alignment film are sequentially laminated on a transparent base, a projection side base on a transparent base in which a transparent electrode film and a liquid crystal alignment film are successively laminated, and a liquid crystal, The writing side substrate has a structure in which a liquid crystal is sandwiched between both liquid crystal alignment films on the surfaces of the writing side substrate and the projection side substrate, and a diffraction grating that provides at least two types of optical phase difference to the writing side substrate is periodic in the plane. In the color thermal writing liquid crystal light valve, the color thermal writing liquid crystal light valve is provided with a photoreceiver that is formed in a wafer and generates a clock signal by receiving the diffracted light of the writing light that is reflected and diffracted by the diffraction grating. The at least one type of diffraction grating that provides a plurality of groove directions is a diffraction grating that has a plurality of two-dimensional groove directions, and the at least one type of diffraction grating that has a plurality of two-dimensional groove directions. The specific diffraction grating is a diffraction grating that has one groove direction different from other diffraction gratings and is formed at a depth such that high diffraction efficiency can be obtained for the wavelength of the writing light, The color thermal writing liquid crystal is characterized in that the light receiver is placed at a position to receive only the diffracted light that is reflected and diffracted by the diffraction grating formed at a depth such that high diffraction efficiency can be obtained. light bulb.