JPH0453403B2 - - Google Patents

Description

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

[Conventional technology]

In recent years, there has been a demand for displays that are highly accurate and can be partially rewritten in computer-based image processing, newspaper editing, and LSI design. Display devices with a high resolution of 2000 lines or more include displays that thermally write on liquid crystals using laser light.
For example, the magazine ``Proceeding of the SID''
1978, pp. 1-7, ``Laser Selected Liquid Crystal Projection Display (LASER-ADDRESSED)''
LIQID CRYSTAL PROJECTION
DISPLAY)”.

According to this paper, an image can be recorded by scanning with a laser beam 20 on a liquid crystal light valve 29 as shown in FIG. 5, and the image can be displayed by making the projection light 21 enter and reflect. The liquid crystal light valve 29 includes a light absorption film 23, an aluminum reflection film 24,
It has a structure in which a liquid crystal material 25 is sandwiched between a glass substrate 22 on which a liquid crystal alignment film 28 is formed, and a glass substrate 27 on which a transparent electrode film 26 and a liquid crystal alignment film 28 are formed. When the laser light 20 is incident on the liquid crystal light valve 29, the laser light 20 is absorbed by the light absorption film 23 and converted into heat, which is transmitted through the aluminum reflection film 24 and the liquid crystal alignment film 28 to increase the temperature of the liquid crystal material 25. Smectic liquid crystal is used as the liquid crystal material 25, and the smectic liquid crystal changes into a nematic phase and a liquid phase by increasing the temperature, and when the laser beam 20 is removed, it is rapidly cooled and changes to a liquid state. The random orientation state of the liquid crystal molecules is frozen, and the scattered nuclei are read out by the projection light 21 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 ride valve includes three color filters each consisting of a diffraction grating that provides an optical phase difference so as to diffract visible light in a specific wavelength region in the zero-order direction.
It has a built-in three-color stripe color filter arranged periodically within the type plane, and the color filter can be formed with a very fine width.
It is characterized by 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-phase light valve is received, the first-order diffracted light is passed through three types of color filters. Since the diffraction efficiency of the diffraction grating is different, the intensity is modulated in one-to-one correspondence between the scanning position of the laser beam and the position of the color filter, and the position standard is determined from the electrical signal obtained from the optical receiver. By extracting the signal from a specific color filter and using it as a writing position reference clock signal, writing to each color filter position is performed by setting an appropriate delay time from the position reference clock signal and connecting the laser beam to the liquid crystal light. By providing a sufficient amount of light for writing to the bulb, each pixel can be written with good positional accuracy.

[Problem that the invention seeks to solve]

However, the electrical signal obtained by receiving the first-order diffracted light that has been intensity-modulated in one-to-one correspondence with the color filter position has a small modulation amplitude as shown in FIG. In order to always extract the signal from the filter of a specific color regardless of the color, a gate circuit is required, making signal processing complicated.

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, and to be able to receive the first-order diffracted light from a specific color filter without using a gate circuit, regardless of changes in the amount of writing light, and to perform modulation without using a gate circuit. It is an object of the present invention to provide a color thermal writing liquid crystal ride valve which can obtain a position-based clock signal with a large amplitude and facilitates signal processing for controlling the writing position.

[Means for solving problems]

The color thermal writing liquid crystal ride valve of the present invention comprises:
A transparent substrate, a light-absorbing film, a light-reflecting film, a liquid crystal alignment film, a liquid crystal, a liquid crystal alignment film, a transparent electrode film, and a transparent substrate are sequentially laminated, and a specific layer is formed between the above components. A color thermal writing liquid crystal in which a multi-color filter is formed by periodically arranging at least two types of color filters each consisting of a diffraction grating that has an optical phase difference so as to diffract visible light in the wavelength range of . In the light valve, the groove direction of at least one type of diffraction grating among the diffraction gratings of the multicolor filter is formed and configured to be different from the groove direction of other diffraction gratings.

[Principle and operation of the invention]

A multi-color filter, in which at least two types of color filters consisting of diffraction gratings with optical phase differences are arranged periodically in a plane, diffracts only visible light in a specific wavelength range of the projected light, and displays the color on the projection screen. In addition to the function of displaying, it also scans the liquid crystal light valve with a writing laser beam at a light intensity below the writing threshold, and by receiving the diffracted light, it can determine the mutual positional relationship between the color filter and the writing light. This has the effect of allowing writing to be performed with good positional accuracy. Here, if the groove direction of at least one type of diffraction grating used as a position reference among the diffraction gratings of the multicolor filter is formed to be different from the groove direction of the other diffraction gratings, the writing laser beam can be directed to the liquid crystal light valve. When scanning with a light intensity below the writing threshold, the diffracted light from the diffraction grating used as a position reference is diffracted in a different direction because the groove direction is different from that of other diffraction gratings, so it is received separately from other diffracted lights. The electric signal obtained by receiving the light has a larger modulation amplitude than that of the conventional example, and moreover, a signal from a filter of a specific color that is always used as a position reference can be obtained regardless of changes in the amount of writing light. Therefore, if this electrical signal is used as a position-based clock signal for writing, writing to each color filter position requires an appropriate delay time from the position-based clock signal, which is sufficient for the laser beam to write on the liquid crystal light valve. By providing a sufficient amount of light, each pixel can be written with high positional accuracy.

FIG. 6 is a diagram showing the principle of a color filter using a diffraction grating used in the present invention. In FIG. 6, there is a reflective diffraction grating in which the surface of a substrate 30 having rectangular irregularities with a depth d is coated with a reflective film 31, and when white light 32 is incident on this, the 0th order diffraction light 33 is mainly , +1st-order diffracted light 34, and -1st-order diffracted light 35 are diffracted. The +1st-order diffracted light 34 and the -1st-order diffracted light 35 are diffracted in different directions depending on the wavelength.
The direction of diffraction depends on the pitch of the diffraction grating. The wavelength distribution of the 0th order diffracted light 33 returning in the specular reflection direction depends on the depth d.

The 0th-order diffracted light intensity η of an arbitrary wavelength λ can be obtained by the following equation, where n is the refractive index of the medium through which the light travels.

η=cos ² (2πnd/λ) ...(1) Equation (1) takes the maximum value 1 when the depth d of the grating satisfies the following equation.

d=mλ/2n (m is an integer)...(2) Also, the minimum value is 0 when the depth d of the grating satisfies the following equation.

d=(2m+1)λ/4n (m is an integer) ...(3) In Figure 7, the refractive index of liquid crystal is 1.5, where n is the refractive index.
The value of the depth d 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.

〔Example〕

FIG. 2 is a diagram showing an embodiment of a multicolor filter used in a color thermal writing liquid crystal light valve according to the present invention. The multi-color filter has three colors: red 41, green 42, and blue 43, and the refractive index of the liquid crystal
1.5, the depth of the grating is 290 nm, respectively.
The wavelengths are 520 nm and 240 nm, and 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 glass substrate. However, the lattice constants of the diffraction gratings do not have to be the same for all three types.

In order to engrave the diffraction grating shown in Figure 2 on a glass substrate, first, the diffraction grating of one type of color filter is formed on the glass substrate masked with photoresist by chemical etching, ion milling, etc., and this procedure is followed. By repeating the process twice by changing the position and depth, a diffraction grating of a three-color color filter can be formed. Alternatively, a similar multicolor filter can be obtained by forming a diffraction grating by patterning a photosensitive resin, or by taking a replica and transferring it to a plastic resin. When the refractive index of the glass substrate is 1.47 and the wavelength of the writing laser beam is 0.83 μm, the first-order light diffraction efficiency of the diffraction grating corresponding to the red, green, and blue color filters is 8.3%, 9.2%, and 0.3%, respectively. Therefore, in order to receive the first-order diffracted light and obtain a reference signal for the writing position, it is appropriate to use the first-order diffracted light from red or green.
The direction of the groove 35 of only the second diffraction grating is the same as that of the groove 44 of the other red and blue color filters 41 and 43.
46 is formed in a different direction. In addition to the three colors of red, green, and blue, the multicolor filter also has three colors of blue-green, purple, and yellow, or blue-green, purple, yellow,
It is also possible to use the four colors of red, and in order to obtain a position-based signal, the groove direction of the diffraction grating of one or two of the color filters may be formed to be different from the groove direction of the other diffraction gratings. good.

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. 5 in that a diffraction grating 5 shown in FIG. 2 is engraved on the glass substrate 4 on the writing laser beam 2 side. 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 absorption film, and a dielectric multi-interference film are formed by vapor deposition, and further as a reflective film 7.
An Al film is deposited, and a polymer film, an SiO film by oblique vapor deposition, 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 a liquid crystal alignment film 8 is further formed. The liquid crystal 9 is a smectic liquid crystal, such as OCBP (octyl cyano biphenyls) or DCBP (octyl cyano biphenyls).
biphenyl) or a mixture thereof.

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 using red, green, and blue color filters to generate a color image, to obtain a red image,
All you have to do is write with a laser beam on the liquid crystal part 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 can be obtained by foil color mixing. Furthermore, by controlling the amount of laser light for writing and providing gradation, full-color images can be realized.

Regardless of the nonlinearity of the optical scanning writing optical system,
Select the position of each color filter and laser beam 2
In order to irradiate and write on the liquid crystal, it is necessary to know the positional relationship between the laser beam 2 and each color filter.
For this purpose, the laser beam 2 scans the liquid crystal light valve 1 with a constant light intensity below the writing threshold during the horizontal scanning period by the optical deflector 3. When the laser beam 2 scanned the diffraction gratings corresponding to the red and blue filters, the +1st-order diffraction light 12 and -1st-order diffraction light 13 shown by broken lines were reflected and diffracted, and scanned the diffraction gratings corresponding to the green filter. In this case, +1st-order diffracted light 14 and 15 shown by dotted lines are reflected and diffracted. In this way, the ±1st-order diffracted lights 14 and 15 from the diffraction grating corresponding to the green filter are the other ±1st-order diffracted lights 1
2 and 13 have different diffraction directions, and can be separately received by the light receiver 16. However, ±1st-order diffracted light 14,
It is only necessary to receive at least one of the 15 lights. Since the electrical signal obtained from the photoreceiver is obtained only when the laser beam 2 is scanning the green color filter 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 write the laser beam with sufficient light intensity to write to the liquid crystal light valve. This is done by giving

FIG. 3 is a diagram showing an example of an electrical signal obtained by receiving first-order diffracted light. Compared to the conventional example shown in FIG. 4, it is 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.

〔Effect of the invention〕

As described in detail above, in this invention, regardless of changes in the amount of writing light, the clock signal for writing position control can always be obtained from the filter of a specific color with the position reference. This has the effect of making it possible to create a highly saturated color display that prevents color mixing.

[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. 4 is a diagram showing a light receiver signal obtained by the present invention, FIG. 4 is a diagram showing a conventional light receiver signal, FIG. 5 is a sectional view showing a conventional liquid crystal light valve, and FIG.
7 are diagrams showing the principle of wavelength selection of the diffraction grating used in the present invention. 1...Color thermal writing liquid crystal light bulb, 2...
... Laser light, 3 ... Light deflector, 4 ... Glass substrate, 5 ... Diffraction grating, 6 ... Light absorption film, 7 ... Reflection film, 8 ... Liquid crystal alignment film, 9 ... Liquid crystal, 10 ... …
Transparent electrode film, 11...Glass base, 12...+1
Next-order diffracted light, 13...-1st-order diffracted light, 14...+1
Next-order diffracted light, 15...-first-order diffracted light, 16... Light receiver, 17... Writing lens.

Claims (1)

[Claims] 1. A transparent substrate, a light absorption film, a light reflection film, a liquid crystal alignment film, a liquid crystal, a liquid crystal alignment film, a transparent electrode film, and a transparent substrate are sequentially laminated, and there is no space between the above components. A color thermal writing liquid crystal in which a multi-color filter is formed by periodically arranging at least two types of color filters made of diffraction gratings with an optical phase difference so as to diffract visible light in a specific wavelength range. In the light valve, the color thermal writing liquid crystal light valve is characterized in that the groove direction of at least one type of diffraction grating among the diffraction gratings of the multicolor filter is formed to be different from the groove direction of other diffraction gratings. .