JPH0820631B2 - Thermal writing liquid crystal projection display - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat writing liquid crystal projection display, and more particularly to a heat writing liquid crystal projection display capable of high-definition display using a liquid crystal light valve.

[Conventional technology]

In recent years, in image processing using a computer, newspaper page editing, or LSI design, a highly accurate and partially rewritable display is desired. With the CRT (cathode ray tube) used in the past, it is difficult to raise the resolution to 2000 or more, and the scanning speed of the electron beam also increases, which causes flickering on the screen. In addition, the display device using the storage tube has a low screen brightness in order to prevent the deterioration of the phosphor, and the device cannot be erased partially, and the device is expensive.

Further, as a high-precision display having a resolution of 2000 or more, there is a display in which liquid crystal is thermally written by laser light.

FIG. 3 is a cross-sectional view of a liquid crystal light valve for explaining such a conventional example.

As shown in FIG. 3, laser light is emitted to the liquid crystal light valve 30.
An image can be recorded by scanning with 31, and the above image can be displayed by causing the projection light 32 to enter and reflect. The liquid crystal light valve 30 includes a glass substrate 33 having a light absorption film 35, a light reflection film 36, and a liquid crystal alignment film 38, a transparent electrode film 37, and a liquid crystal alignment film 38.
A liquid crystal material 39 such as a smectic liquid crystal is sandwiched between the glass substrate 34 and the glass substrate 34. When the laser light 31 enters the liquid crystal light valve 30, the laser light 31 is absorbed by the light absorption film 35 and converted into heat, and this heat is reflected by the light reflection film 36 and the liquid crystal alignment film.
The temperature of the liquid crystal material 39 is raised along the line 38. Further, the above-mentioned smectic liquid crystal changes to a nematic phase or a liquid phase by increasing the temperature. Therefore, when the laser light 31 is removed, the frozen scattering nuclei in the liquid crystal random liquid crystal molecule alignment state produced by quenching are read out by the projection light 32 and displayed as pixels on the screen.

[Problems to be solved by the invention]

However, since the conventional thermal writing liquid crystal projection display displays the scattered and non-scattered pixels of the liquid crystal by the schlieren optical system, the image contrast depends on the scattered state of the liquid crystal, and the contrast is essentially reduced. It has the drawback that it cannot be raised.

Further, although the output of the writing laser beam may be increased as a means for increasing the contrast, there is a drawback that the display device itself becomes large when a high output laser device is used. Further, although the contrast can be increased even if the writing speed is slowed, this also has a disadvantage that it takes a lot of time to display one screen.

It is an object of the present invention to provide a thermal writing liquid crystal projection display that improves the contrast of images and improves the writing speed.

[Means for solving problems]

The thermal writing liquid crystal projection display of the present invention comprises a liquid crystal light valve, an optical scanning writing optical system, a polarizer and an analyzer, and projects the image drawn on the liquid crystal light valve by the optical scanning writing optical system. Has an optical system,
The polarization axes of the polarizer and the analyzer are arranged to be approximately 45 degrees with respect to the liquid crystal horizontal alignment direction of the liquid crystal light valve.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A to 1C are perspective views showing various states of a liquid crystal cell for explaining the principle of the present invention.

FIG. 1 (a) shows the case where the liquid crystal molecules in the liquid crystal cell 1a are vertically aligned (homeotropic) in which the glass substrates 1b and 1c are vertically aligned, and FIG. 1 (b) shows the horizontal alignment (homogeneous). In the case of), FIG. 1 (c) shows the case where the image is written by the laser beam in the scattering state, respectively, and a polarizing plate (not shown: left and right sides of the liquid crystal cell 1a) corresponding to the polarizer and the analyzer, respectively. Are arranged on both sides of the liquid crystal cell 1a, and the polarization axes of these polarizing plates (double-headed arrow)
This shows the optical (polarization) characteristics of the incident light when they are arranged so that the angle between the liquid crystal horizontal alignment direction [vertical direction in FIG. 1 (b)] is 45 °. Here, the incident light is natural light, but when transmitted through a polarizing plate arranged on the left side of the liquid crystal cell 1a, it is converted into linearly polarized light having a polarization direction of 45 ° with respect to the horizontal alignment direction of the liquid crystal and enters the liquid crystal cell 1a. To do.

That is, liquid crystal has a refractive index anisotropy having an optical axis in the major axis direction of liquid crystal molecules. However, as shown in FIG. 1A, in the case of vertical alignment, the incident linearly polarized light passes through the liquid crystal cell 1a as it is without changing the polarization state. Therefore, even if this light passes through the right-sided polarizing plate (analyzer) that has the same polarization axis as the left-sided polarizing plate (polarizer), its transmission is eliminated except for the slight absorption of the right-sided polarizing plate. The light intensity does not change.

On the other hand, as shown in FIG. 1 (b), in the case of horizontal alignment,
When linearly polarized light having a polarization direction of 45 ° with the liquid crystal horizontal alignment direction is incident, a phase shift occurs between the ordinary and extraordinary light components, and the transmitted light is generally elliptically polarized light. The amount of this phase shift depends on the birefringence of the liquid crystal and the thickness of the liquid crystal layer, and the amount of phase shift is 45 degrees with respect to the long axis direction of the liquid crystal molecules.
It becomes the largest at ゜. For example, when the phase shift is 90 ° and 270 °, the transmitted light of the liquid crystal cell 1a becomes circularly polarized, and when the phase shift is 180 °, it becomes linearly polarized with the polarization direction rotated by 90 °.

When the polarizing plate (analyzer) is arranged on the right side of the liquid crystal cell 1a having the same polarization axis as the polarizing plate (polarizer) arranged on the left side of the liquid crystal cell 1a, the transmitted light of the polarization state is transmitted. The amount of light decreases depending on the polarization state. For example, when the phase shift is 90 ° and 270 °, the amount of transmitted light becomes half because of circularly polarized light, and when the phase shift is 180 °, the amount of transmitted light becomes zero because of orthogonal linearly polarized light. In the case of general elliptically polarized light, the amount of transmitted light decreases according to the polarization state.

Next, the relationship with the thermal writing liquid crystal projection type display of the present invention will be described. A liquid crystal light valve described later represented by the liquid crystal cell 1a is shown in FIG. 1 when an erasing voltage for erasing a written image is applied. The vertical orientation of (a) is shown, and this state becomes a white screen on the screen. Also, the liquid crystal cell 1a
FIG. 1 (b) shows the horizontal orientation when the film is gradually cooled, but this state is not used for direct display. Then, the writing pixel shows the scattering state of FIG. 1 (c), and this state becomes black on the screen. The scattering state of the writing pixel does not become a completely isotropic scattering state due to the addition of the alignment regulating force by the glass substrates 1b and 1c and the surrounding liquid crystal state, and has a horizontal alignment component and a vertical alignment component. Therefore, the conventional projection using the Schlieren optical system, that is, the method of projecting only regular reflection on the screen has a limit in improving the contrast. Conversely, since the writing pixel has a horizontal orientation component, when linearly polarized light is incident, the transmitted light becomes elliptically polarized light, as in FIG. 1 (b). Therefore, when projection is performed using linearly polarized light in addition to the Schlieren optical system, the horizontal alignment component of the scattering pixels causes a phase shift in the incident linearly polarized light, and the transmitted light is changed to elliptically polarized light. Therefore,
Since the analyzer can reduce only the amount of light transmitted through the scattering pixels, the contrast of the image can be improved.

The present invention is based on the above principle, and by using a polarizer and an analyzer, high contrast projection display is possible. That is, the projection optical system of the thermal writing liquid crystal projection display of the present invention comprises a polarizer and an analyzer in addition to the conventional Schlieren optical system, and the polarization axes of the polarizer and the analyzer are relative to the horizontal alignment direction of the liquid crystal. By setting the direction to approximately 45 °, the phase shift of the scattering pixels is greatly changed and the amount of transmitted light is reduced, so a thermal writing liquid crystal projection type capable of displaying a high-contrast image without significantly changing the device configuration. You can get a display.

FIG. 2 is a block diagram of a thermal writing liquid crystal projection display for explaining one embodiment of the present invention.

As shown in FIG. 2, the liquid crystal light valve 1 is of the same reflection type as the conventional liquid crystal light valve, but the optical scanning optical system 2 includes a laser light source and a scanning mirror for two-dimensionally scanning the laser light 3. Including this, as the scanning mirror, galvanometer scanner and resonant scanner,
A polygon mirror scanner or the like can be used. To write an image on the liquid crystal light valve 1, the laser beam 3 is two-dimensionally scanned and a switching operation corresponding to the image data is performed. Further, the writing lens 4 for writing an image on the liquid crystal light valve 1 is provided with a laser beam 3
Is a lens for condensing so as to have an energy density necessary for writing, and in this embodiment, a −θ lens is used in order to give linearity to scanning.

On the other hand, the projection optical system includes a light source 5 which is a white light source such as a halogen lamp or a xenon lamp, projection lenses 7 and 8 and a reflection mirror 10 which form a Schlieren optical system, and a polarizing plate 9. With this configuration, only the reflected light (regularly reflected light) from the non-scattering pixels among the scattering and non-scattering pixels written in the liquid crystal light valve 1 is projected as the projection light 11 on the screen 12 to obtain a black and white image display. be able to. The above-mentioned polarizing plate 9 also serves as a polarizer and an analyzer here, and is arranged so that the polarization axis thereof is in the direction of 45 degrees with respect to the liquid crystal horizontal alignment of the liquid crystal light valve 1. However, the incident light 6 obtained from the two projection lenses 7 and 8 from the light source 5 is incident on the liquid crystal light valve 1 as linearly polarized light by the polarizing plate 9, but the phase changes only in the scattering pixel portion due to the birefringence of the liquid crystal. The reflected light becomes elliptically polarized light. Therefore, the light quantity of the scattering pixels, that is, the light quantity of the portion projected as a black pixel on the screen can be further reduced by the polarizing plate 9 which also functions as an analyzer, so that a high-contrast image is projected on the screen 12. be able to.

According to the above-described thermal writing liquid crystal projection display of the present embodiment, the light quantity of the scattering pixels can be reduced to 1/3, display of a high-contrast image three times or more can be realized without significantly changing the device configuration, and If the contrast is the same as that of the conventional pixel, there is an advantage that it can be displayed at a speed twice or more.

Although the present embodiment has been described with respect to the reflective liquid crystal light valve, a transmissive liquid crystal light valve can be similarly applied. Further, although the polarizing plate is used as the polarizer and the analyzer, an optical element for obtaining linearly polarized light from indefinite polarized light such as a polarizing beam splitter may be used,
If a polarizer is provided between the light source 5 and the liquid crystal light valve 1 and an analyzer is provided between the liquid crystal light valve 1 and the screen 12, the same result can be obtained.

〔The invention's effect〕

As described above, the thermal writing liquid crystal projection display of the present invention uses the projection optical system utilizing polarized light in addition to the conventional Schlieren optical system to increase the image contrast several times or more than the conventional one and There is an effect that the speed can be improved.

[Brief description of drawings]

1 (a) to 1 (c) are perspective views showing various states of a liquid crystal cell for explaining the principle of the present invention, and FIG. 2 is a thermal writing liquid crystal for explaining one embodiment of the present invention. FIG. 3 is a configuration diagram of a projection display, and FIG. 3 is a sectional view of a liquid crystal light valve for explaining a conventional example. 1 ... Liquid crystal light valve, 2 ... Optical scanning optical system, 3 ...
Laser light, 4 ... Writing lens, 5 ... Light source, 6 ... Incident light, 7,8 ... Projection lens, 9 ... Polarizing plate, 10 ... Reflecting mirror, 11 ... Projection light, 12 ... Screen .

Claims (1)

[Claims] 1. A liquid crystal light valve, an optical scanning writing optical system, and a projection optical system having a polarizer and an analyzer for projecting an image drawn on the liquid crystal light valve by the optical scanning writing optical system. The heat writing liquid crystal projection display, wherein the polarization axes of the polarizer and the analyzer are arranged at an angle of about 45 degrees with respect to the liquid crystal horizontal alignment direction of the liquid crystal light valve.