JPS63135990A - Color thermally writing liquid crystal projection type display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to high viscosity color displays with laser thermal writing.

(Prior Art) In recent years, there has been a demand for displays with high precision and the ability to partially write on images in computer-based image processing, newspaper editing, and LSI design.

Conventionally used CRTs (cathode ray tubes) have a resolution of 2
It is difficult to increase the number of lines above 000, and the scanning speed of the electron beam becomes faster, which causes flickering on the screen.
Furthermore, display devices using storage tubes have the disadvantage that the screen brightness is low to prevent deterioration of the phosphor, partial erasure cannot be performed, and the device is expensive.

Display devices with a high resolution of 2,000 lines or more include displays that perform thermal writing using a liquid crystal laser beam.This thermal writing liquid crystal projection type display is described in, for example, the magazine ``Proceeding of theS, 1.D,
), 1978, pages 1-7, in the article LASER-ADDRESSED
LIQUID CRYSTAL PROJECTION
DISPLAY) J. According to this paper, an image can be recorded by scanning with a laser beam on a liquid crystal light valve as shown in FIG. 5, and the image can be displayed by projecting light onto a reflective film. The liquid crystal light valve 79 includes a light absorption film 73 and an aluminum reflection film 7.
4. A glass substrate 72 on which a liquid crystal alignment film 78 is formed, a glass substrate 77 on which a transparent electrode film 76 and a liquid crystal alignment film 78 are formed.
It has a structure in which a liquid crystal material 75 is sandwiched between the two. When the laser beam 70 enters the liquid crystal light valve 79, the laser beam 70
is absorbed by the light absorption film 73 and converted into heat, which is transmitted through the aluminum reflection film 74 and the liquid crystal alignment film 78 to increase the temperature of the liquid crystal material 75. A smectic liquid crystal is used as the liquid crystal material 75, and the smectic liquid crystal changes to a nematic phase and a liquid layer by increasing the temperature, and when the laser beam 70 is removed, it is rapidly cooled to form random liquid crystal molecules in the liquid state. The orientation state is frozen and becomes a scattering nucleus, which is read out by the projection light 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. To perform a color display, it is sufficient to irradiate a plurality of liquid crystal display elements with different monochromatic lights and to project and synthesize the images. In order to combine multiple images and avoid color shift, the projection optical system must have high precision, and multiple laser writing optical systems are required, making the device extremely expensive. There wasn't.

Furthermore, regarding a method for displaying at least three colors with one liquid crystal light valve, Japanese Patent Application No. 60-2262
41 'Color Thermal Writing Liquid Crystal Light Valve'. According to the above invention, the liquid crystal light valve has a built-in color filter made 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, and the color filter has a built-in color filter. It can be formed into very fine widths and has excellent light and heat resistance. A multi-color filter, in which a color filter consisting of a diffraction grating giving an optical phase difference is arranged periodically in a plane of at least the Zffl type, diffracts only the visible light in a specific wavelength range of the projected light, and displays the color on the projection screen. In addition to displaying functions, it also scans the writing laser beam with a light intensity below the threshold for writing on the liquid crystal light valve.
By receiving the diffracted light, the mutual positional relationship between the color filter and the writing light can be known, and writing can be performed with high positional accuracy. here,
Among the diffraction gratings of a multicolor filter, if the groove direction of at least one type of diffraction grating used as a position reference is formed to be different from the groove direction of other diffraction gratings, the threshold value for writing the writing laser beam into the liquid crystal light valve When scanning with the following light intensity, 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 can be received separately from other diffracted lights. The electrical signal obtained by this method 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 the writing position reference clock signal, then
To write to each color filter position, each pixel can be written with high positional accuracy by setting an appropriate delay time from the position-based clock signal and giving the laser beam a sufficient amount of light to write on the liquid crystal light valve. becomes possible.

(Problems to be Solved by the Invention) However, in the method according to the invention described above, there are cases in which the position-based color filter for extracting the clock signal is irradiated with the amount of laser light necessary for writing, and cases in which it is irradiated with the amount of light below the writing threshold. The intensity of the clock signal obtained may differ depending on the case, and even when the writing laser beam is incident on a color filter different from the position reference, the amount of light may wrap around the position reference color filter and the desired color may not be generated. , which had the disadvantage of causing color shift in some areas.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color thermal writing liquid crystal projection display that eliminates the above-mentioned drawbacks, provides a large screen with high precision, and is capable of displaying at least three colors.

(Means for Solving the Problems) According to the present invention, a liquid crystal light valve, a monochromatic light source,
In a thermal writing liquid crystal projection display comprising an optical scanning writing optical system and a projection optical system for projecting an image drawn on the liquid crystal light valve by the optical scanning writing optical system, the monochromatic light source has polarization planes perpendicular to each other. The liquid crystal light valve is composed of a plurality of monochromatic light sources, and the liquid crystal light valve has three types of color filters, each consisting of a diffraction grating, which is provided with an optical phase difference so as to diffract visible light in a specific wavelength range in the zero-order direction, in a periodic manner within the plane. The optical scanning writing optical system includes a monochromatic light source, a light modulator that modulates a plurality of monochromatic lights from the monochromatic light source, and a two-dimensional three-color stripe color filter arranged in three-color stripes. a lens that converges the plurality of monochromatic lights; and a polarizing filter that detects one of the plurality of monochromatic lights reflected and diffracted by the color filter in the liquid crystal light valve. A color thermal device comprising: a light receiver; a circuit that generates a clock signal from an electrical signal obtained from the light receiver; and a circuit that provides an image input signal to the optical modulator in synchronization with the clock signal. A writeable liquid crystal projection display is obtained.

(Principle and operation of the invention) Two laser beams are used: a laser beam that scans with a light intensity below a threshold value for extracting a clock signal, and a laser beam that writes on a liquid crystal light valve with a light intensity above the threshold value. If only the laser light for extracting the clock signal can be detected from among the diffracted light obtained by entering the liquid crystal light valve, the above-mentioned problems can be solved. Using laser beams with different directions, the light diffracted from the liquid crystal light valve is passed through a polarizing plate, and only the laser beam for extracting the clock signal is extracted and detected, thereby producing a clock signal without fluctuations in intensity level and without interference. can get.

(Embodiment) FIG. 1 is a diagram showing an embodiment of a color thermal writing liquid crystal projection display according to the present invention. Laser light 30.30' from the laser light source 1 and laser light R2 passes through the frimeter lenses 3, 3' and becomes parallel light, and the plane of polarization of the laser light 30' is rotated by 90° by the half-wave plate 4. As a result, the plane of polarization becomes orthogonal to the laser beam 30. Laser light 30.3
0' is then combined into one laser beam 31 by the polarizing beam splitter 5. This combined laser beam 31 is scanned by an optical scanner 6 onto a liquid crystal light valve 9 while being focused through a lens 8. At this time, the light reflected and diffracted from the liquid crystal light valve 9 passes through a lens 8 and a polarizing filter 16, and then is detected by a photodetector 17. When the polarization axis of the polarizing filter 16 is made to coincide with the polarization axis of either of the laser beams 30 and 30', only the reflected and diffracted light of one of the laser beams can be detected. Therefore, when the laser beam 30 is used as a writing beam and the laser beam 30' is used as a clock number 2 detection beam, the laser beam 30' is scanned over the liquid crystal light valve 9 with a light intensity below the threshold value, and the diffracted light is sent to the detector 17. A clock signal can be extracted by detecting the clock signal, and this clock signal is sent to the signal processing circuit 21, and after processing with the image and old name from the control circuit 20, the laser light source 2 is driven by the drive circuit 22. . The laser light source 2 emits a laser beam 30 with an amount of light above a threshold value, and the liquid crystal light valve 9 is scanned together with the laser beam 30' to write an image based on the image signal. At this time, the liquid crystal light valve 9 of the laser beam 30
The reflected and diffracted light is stopped by the polarizing filter 16 and is not detected by the photodetector 17.

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 coated with a reflective film 81 on the surface of a substrate 80 having rectangular irregularities with a depth d.
When 83. is incident, mainly the O-order diffracted light 83. +1st order diffracted light 84
．． −1st order diffracted light 85 is diffracted. +1st order diffracted light 84.
The −1st-order diffracted light 85 is diffracted in different directions depending on the wavelength, and the diffraction direction depends on the pitch of the diffraction grating. The wavelength distribution of the O-order diffracted light 83 returning in the specular reflection direction depends on the depth d.

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

77 = cos” (2yr n d/in)
- (1) Equation (1) has a maximum value of 1 when the depth ed of the lattice satisfies the following expression.

d=mλ/ 2 n (m is an integer) − (2) Moreover, the minimum value O is obtained when the depth d of the grating satisfies the following formula.

d-(2m+1)λ/4n (m is an integer) (3) In Figure 7, the refractive index n is 1.5°, and the depth ad of the diffraction grating is (a) 290 nm, ( b)
520nfn, (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. 2 is a diagram showing a specific example of a multicolor filter for color thermal writing liquid crystal light pulp used in the present invention. Multi-color filter: 41 red, 42 green. blue 43
When the refractive index of the liquid crystal is 1.5, the depth of the diffraction grating is 290 nm and 520 nm, respectively.

240 nm, the lattice constant of the diffraction grating is 2− and 10−
One pixel is formed with a size of ×30−. Therefore 30
Red, green, and blue filters can be arranged in too many pixels on a mm square glass substrate. However, the lattice constants of the diffraction gratings do not have to be the same for all three types.

To imprint 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. By changing the depth and repeating the process twice, a diffraction grating of a three-color color filter may be formed. In addition, 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. The refractive index of the glass substrate is 1.47. The wavelength of the writing laser beam is 0.83
/Jm, the first-order light diffraction efficiencies of the diffraction gratings corresponding to red, green, and blue color filters are 8.3% and 9.9%, respectively.
2% and 0.3%, it is necessary to receive the first-order diffracted light and obtain the reference signal for the writing position from the red or green one.
It is appropriate to use the second-order diffraction light, and in FIG.
4 and 46. The multi-color filter has three colors: red, green, and blue, as well as blue-green and purple.

It is possible to use three colors (yellow) or four colors (blue-green, purple, yellow, and red), and in order to obtain a position-based signal, the direction of the grooves in the diffraction grating of one or two color filters is set to the other. The groove direction may be different from that of the diffraction grating.

FIG. 3 is a perspective view of a specific example of a color thermal writing liquid crystal light valve used in the present invention. The color thermal writing liquid crystal light valve 1 has the following features compared to the liquid crystal light valve shown in FIG.
The difference is that the diffraction grating 55 shown in FIG. 2 is completely engraved on the glass substrate 54 on the writing laser beam 52 side. glass base 54
As a light absorption film 56, a II-VI group compound semiconductor film containing Cd, a ■-■ group compound semiconductor film containing Te, two absorption films, and one multi-interference film are formed by vapor deposition or the like, and a reflection film is further formed on the light absorption film 56. An AM film is deposited as a film 57, and a polymer film, an SiO film or the like by oblique vapor deposition is formed thereon as a liquid crystal alignment film 58. Also,
On the other substrate 61, an ITO (indium tin oxide) film is attached as a transparent electrode film 60, and a liquid crystal alignment film 58 is further formed. As the liquid crystal 59, a smectic liquid crystal such as OCRP (octyl cyano biphenyl), DCBP (octyl cyano biphenyl), or a mixed material thereof can be used.

Writing in the color thermal writing liquid crystal light valve 51 constructed in this manner is performed in the same manner as in the conventional art by irradiating the laser beam 52. For example, when using red, green, and blue color filters for color image generation,
To obtain a red image, write with a laser beam on the liquid crystal area 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 are obtained by additive color mixing. Furthermore, by controlling the amount of laser light for writing and providing gradation, full-color images can be realized.

Regardless of the non-yXB nature of the optical scanning writing optical system, it is necessary to know the positional relationship between the laser beam 52 and each color filter in order to select the position of each color filter and irradiate the laser beam 52 to write on the liquid crystal. There is.

For this purpose, the laser beam 52 scans with a constant light amount below the threshold value for writing into the liquid crystal light valve 51 during the horizontal scanning period by the optical polarizer 53 . When the laser beam 52 scans the diffraction grating corresponding to the red and blue filters, +
1st order diffracted light 63. When the −1st-order diffracted light 64 is reflected and diffracted and scanned over a diffraction grating corresponding to a green filter, +1st-order diffracted light 65 and −1st-order diffracted light 62 shown by dotted lines are reflected and diffracted. In this way, the ±1st order diffracted light 65.62 from the diffraction grating corresponding to the green filter is the other ±1st order diffracted light 63.
, 64 and the polarizing plate 68 . Light receiver 66
It is possible to separate and receive the light. However, ±1st order diffracted light 65
．． The electrical signal obtained from the light receiver is obtained only when the laser beam 52 scans the green color filter used as the position reference, so this is used as the position reference clock. It can be a signal. Writing in each color filter position is red,
When there are green and blue image signals, this 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 on the liquid crystal light valve.

FIG. 4 is a diagram showing an example of an electrical signal obtained by receiving first-order diffracted light. It is possible to obtain a clock signal for controlling the writing position with a constant modulation amplitude regardless of changes in the amount of writing light.

(Effects of the Invention) As described in detail above, the present invention allows the clock signal for controlling the writing position to be constantly obtained from the filter of a specific color with the position reference regardless of the presence or absence of the amount of writing light. , each pixel is written in the position of the color filter with high precision, and a high chroma color display that prevents color mixing is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a color thermal writing liquid crystal projection display according to the present invention, and FIG. 2 is a diagram showing a specific example of a multicolor filter for a color thermal writing liquid crystal light valve used in the present invention. FIG. 3 is a perspective view showing a specific example of a color thermal writing liquid crystal light valve used in the present invention, FIG. 4 is a diagram showing a receiver signal obtained by the present invention, and FIG. 5 is a diagram showing a conventional liquid crystal light valve. Sectional view, No. 6
7 and 7 are diagrams showing the principle of wavelength selection of the diffraction grating used in the present invention. 1.2... Laser light source, 4... Half wavelength plate, 5
... Polarizing beam splitter, 6... Optical scanner, 9.
・・LCD light valve, 3, 3', 8.11.12
... Lens, 10... Projection light source, 16... Polarizing plate, 17... Photodetector.

Claims (1)

[Claims] A thermal writing liquid crystal projection display comprising a liquid crystal light valve, a monochromatic light source, an optical scanning writing optical system, and a projection optical system that projects an image drawn on the liquid crystal light valve by the optical scanning writing optical system, The monochromatic light source is composed of a plurality of monochromatic light sources with orthogonal polarization planes, and the liquid crystal light valve is formed from a diffraction grating that has an optical phase difference so as to diffract visible light in a specific wavelength region in the zero-order direction. Three types of color filters are arranged periodically within the plane.
The optical scanning writing optical system includes a color stripe color filter, and includes a monochromatic light source, a light modulator that modulates a plurality of monochromatic lights from the monochromatic light source, and a light deflector that deflects the plurality of monochromatic lights two-dimensionally. a light receiver comprising a lens that converges the plurality of monochromatic lights, and a polarizing filter that detects one of the plurality of monochromatic lights reflected and diffracted by the color filter in the liquid crystal light valve; A color thermal writing liquid crystal projection display comprising a circuit that generates a clock signal from an electrical signal obtained from the light receiver, and a circuit that provides an image input signal to the optical modulator in synchronization with the clock signal. .