JPH05150209A - Image display device and its display method - Google Patents

Abstract

PURPOSE:To provide the large-area color display device which generates an image of high quality with high contrast and chroma and small color blurring and facilitates its maintenance, inspection, adjustment, etc. CONSTITUTION:Laser light corresponding to the primary colors of light is used as the source light of the color display device and, preferably, polarized in one direction; and the beams of respective laser devices 110-112 are put together into one axis by using optical devices 107-109, etc., such as half-mirrors; and this beam is given proper divergence by an optical device 105 and irradiate a reflection type two-dimensional optical switch device 103 such as a light valve and its reflected light is projected on a screen 101. A display device 104 such as a CRT operating the two-dimensional optical switch device and the respective laser devices 110-112 are connected to a video controller 117 by cables 113-116 so that the respective lasers emit laser light pulses at proper timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention two-dimensionally changes optical reflection characteristics by light having image information from the outside, and irradiates this with light from the outside as probe light to obtain an image according to the reflection characteristics. The present invention relates to a device for reflecting light (reflection-type two-dimensional optical switch device), a projection-type image display device having such a reflection-type two-dimensional optical switch device and a projection light source, and an image display method used in the device.

[0002]

2. Description of the Related Art As a conventional electric image display device, a cathode ray tube (CRT) such as a cathode ray tube has been known. CR
T is for deflecting an electron beam emitted from an electron gun in an arbitrary direction by the action of an electric field, a magnetic field, or the like, thereby displaying an image. Since this method is extremely simple and a clear image can be obtained, it is still a major part of the display device even more than 70 years after its invention.

In recent years, with the development of video software, there is a tendency for a display device having a larger screen and higher image quality. In this respect, it is hard to say that CRT is excellent. This is because a vacuum device is required to obtain an image by scanning with an electron beam, and in consideration of its durability, a CRT of considerably large size is required. For example, in the case of a diagonal of 30 inches, the thickness of the glass of the CRT becomes more than 1 cm, and the total weight easily exceeds 100 kg.

In order to solve this difficulty, a projection type display device (projection display) has been proposed and spread in recent years. This projection type display device, particularly a device using one type of two-dimensional light amplification device called a light valve, generally has a configuration as shown in FIG. 10, and is a relatively small device, for example, 100 inches. The above large screen can be obtained.

As shown in FIG. 10, a projection display device using a light valve currently on the market generally corresponds to the three primary colors of light of red (R), green (G) and blue (B). Using three dedicated CRTs and their associated light valve devices, they are combined into one screen by the optical system and enlarged and displayed. Therefore, the three light valves and the optical system attached thereto are required to have highly accurate alignment accuracy, specifically, about 1 μm.

In such a projection display device, an image is displayed by an image display device such as a CRT, and a light valve having a diagonal of about 3 to 10 inches is irradiated with the image to display a two-dimensional image on the light valve. The light incident on the light valve and reflected according to the image information is enlarged and displayed on a screen of about 100 inches on a screen 4 to 5 m away. For this reason, a 100-inch display screen is rough, and a light valve for display before enlargement is used so as not to give a blurred display, which is capable of high-definition display. However, in order to suppress the manufacturing cost of the ordinary light valve, for example, it is simply formed by laminating a photoconductive thin film such as amorphous silicon or CdSe and an electro-optical material such as liquid crystal. Was used.

In such a light valve, if the resistivity of the photoconductive layer is low, the electrons generated by the photoelectromotive force generated by the partial irradiation of light may diffuse into the surroundings, resulting in a blurred image. In order to avoid this problem, a sufficiently high resistivity is required as in the photosensitive drum used in an electrostatic copying machine. However, when a material having such a high resistance is used, the pixel The unit product of resistance and capacitance is large, and the light valve cannot keep up with the image speed.

Further, the conductivity of such a photoconductive material is extremely non-linear with respect to incident light, and it is very difficult to display a subtle shading. In particular, since the light incident on the light valve contains image information in an analog manner, gradation display was extremely difficult.

An image display of a conventional light valve display device will be described with reference to FIG. The device comprises a light source 203, display devices 214 to 216 such as a CRT, light valve devices 211 to 213 attached thereto, and a complicated optical device.

First, a light source (usually a metal halide lamp) 203 produces an extremely highly parallel light beam by an optical device 204, which passes through an ultraviolet filter 205 and an infrared filter 206,
It is incident on the polarized semi-transparent film 207. Then, here, a part of the light is reflected and goes toward the bottom of the drawing, and the green filter 208
Thus, only the green color is transmitted and is incident on the light valve 211, is reflected according to the image information, is transmitted through the green filter, and is then incident on the polarization semi-transmissive film 207 again, and a part thereof proceeds to the upper part of the drawing. Of course, there are many light rays that cannot be transmitted because they are reflected by this semipermeable membrane.

On the other hand, the other part of the light incident on the polarized semi-transparent film 207 from the light source direction passes through this, reflects red light, and reaches the mirror 209 transparent to blue light. Then, here, the red color is reflected and goes to the light valve 212 on the lower side of the drawing, and the other colors are transmitted and goes to the light valve on the left side of the drawing. Then, only the blue color reaches the light valve 213 by the blue filter 210.

The red light and the blue light thus reaching each light valve receive a signal corresponding to the image information from the light valve, travel in the reverse direction of the original light path, and are partially transposed by the semipermeable membrane 207. The reflected light travels to the optical device 202 together with the green light and is magnified to the screen 20.
Projected to 1.

The biggest problem with this method is that since the spectrum of the light source is almost white light, and the three colors RGB are extracted from it, most of the light is used for images. Without it, it becomes heat. For this reason, the screen of the existing light valve display device is dark, and an image cannot be displayed under normal room lighting. Therefore, it is necessary to darken the room when displaying an image.

In order to obtain a brighter screen, it is conceivable to use a stronger light source or to widen the transmission spectrum width of the color filter, but the former method causes further heat generation of the device. It is not economical due to the increase in power consumption and the burden on the device for cooling. On the other hand, the latter method narrows the range of colors that can be obtained.

In the conventional light valve display device, since a color filter is used when performing color display, the range of displayed colors is narrower than that of a conventional CRT in consideration of the brightness of the screen. FIG. 7 shows the variety of colors obtained by various display devices. The * mark in the center represents white light. White light is light that is a mixture of light of all wavelengths. And as you go around,
The monochromaticity of light is strengthened, resulting in bright light. The outermost curve shows monochromatic light. Each triangle inside this curve represents the range of colors available on each display. As is clear from the figure,
A conventional light valve display (written as a color filter light valve) is a smaller triangle than a CRT. This is because the light transmitted through each of the RGB three-color filters has a wide spectrum width. The light expressed by the three RGB colors is limited to the inside of a triangle having the three colors as vertices. Further, if the bandwidth of the filter is narrowed in order to enrich the color, the amount of light passing through the filter is reduced and the image becomes dark.

On the other hand, the CRT, which is shown by a dotted triangle in the figure, is considerably larger than the light valve display. This is because the CRT emits light due to the optical transition of inner shell electrons of d orbit and f orbit in the light emitting material excited by the electron beam, and this light emission has an extremely sharp line spectrum. As described above, a display device that uses a color filter such as a light valve display is inferior to a CRT in terms of freedom of color expression and screen brightness.

On the other hand, it is also conceivable to use a light source containing three primary colors having an ideal narrow spectral width, for example, a three-color cold cathode fluorescent tube used in a direct-view LCD, in a light valve display device. In reality, there is no suitable light source because the light source is required to be a point light source due to the necessity of projection.

Further, in terms of finally synthesizing RGB three-color screens, high accuracy is required, and maintenance / maintenance /
Adjustment is extremely time-consuming. In particular, the setting changes slightly depending on humidity and temperature, so in the temperate zone where large demand is expected, conversely there is a great problem in actual use due to the large change in temperature and humidity. There is. In particular, it is extremely difficult to make all the parallelism of light rays having an optical axis system equal to or more than 3 inches and exactly align them on one axis. Also, three such thick optical axes run inside the device, which is the biggest bottleneck in downsizing the device. For the above reasons, it is extremely difficult to obtain an image of 100 inches or more with the conventional light valve display device.

Further, the price of the optical system which requires such a high degree of adjustment is low, and it occupies half of the cost of the apparatus. In addition, the maintenance and inspection requires professional-grade technology, which is difficult for general consumers as well as home electronics sales staff. Therefore, in order to manufacture a low-priced light valve display, the optical system needs to be simple and easy to adjust.

[0020]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the above-described light valve display device. That is, in the present invention,
We propose a projection device that is easy to maintain, inspect, and adjust. It is also desirable that it be low in price. More preferably, it is desirable that it is small and has no problem in installation. For example, in the case where a large amount of heat is generated, many restrictions are added to the place of installation.

Another object of the present invention is to propose a driving method / display method for such a device. In particular, to sufficiently bring out rich color reproducibility, gradation display technology is required more than ever before. The present invention proposes an excellent gradation display technique and a device therefor.

[0022]

In order to solve the above problems, the present invention adopts the following technical ideas. That is, in order to improve the gradation display property of the light valve, the digital gradation method is adopted instead of the analog gradation method.
Therefore, the present invention describes a preferred embodiment of the digital gradation method to be adopted.

Further, in contrast to the conventional light valve having a problem in response speed, there is provided a new light valve device which maintains high speed responsiveness and has little image blurring and blurring. The advantage of high-speed response is indispensable for the digital gradation method.

Further, in the past, the probe light (incident light) to the light valve was broad spectrum and low quality light selected by a color filter, but the present invention uses it as a light beam having a narrower spectrum width. Overcoming, for example, by using laser light. Then, an optical device which is completely different from the conventional method is provided in order to ensure the ease of maintenance, inspection and adjustment, which is one of the further objects of the present invention.

First, the second solution will be described below. As described above, the conventional light valve is a laminated body of uniform thin films and has no boundary between pixels. Therefore, unless a very high resistance material is used, the pixel will be blurred. However, using a high resistance material has a contradiction that the response speed is lowered. Further, the light valve is required to reflect the probe light, but the metal, which is the most easily used reflector, cannot be used because of its low resistance. Therefore, a dielectric multilayer reflective film is used as the reflective film, but its reflection efficiency is 90% or less, and the unreflected light is not absorbed but is transmitted through the reflective film and the underlying amorphous silicon or CdS
Since it reaches the photoconductive layer such as e, it is necessary to purposely form a light-shielding film on the photoconductive layer with the same high resistance semiconductor material.

In the present invention, the technical idea used for such a conventional light valve is greatly revised. First, a metallic material is used as the reflective material. By using a metal material as the reflecting material, not only the reflection efficiency of the probe light can be increased, but also all the unreflected light is absorbed in the metal, so that it is not necessary to provide a light shielding film or the like. However, the use of a low resistance metal material as the reflective material means that the pixels must be provided independently. Therefore, in the present invention, a reflective film is formed for each pixel to interrupt the conduction between the reflective films.

FIG. 5 shows a cross section of a light valve incorporating the technical idea of the present invention. Transparent substrate 501 as in the past
A uniform transparent conductive film 502 is provided on the above, and a uniform transparent conductive film 507 is similarly provided on the other transparent substrate 508, whereby the liquid crystal material 506 is sandwiched. .. If the liquid crystal material is a light-scattering liquid crystal such as a dispersion type (polymer) liquid crystal, the configuration shown in FIG. 5 is sufficient, but if the liquid crystal material is a TN liquid crystal or a ferroelectric liquid crystal, it is necessary to perform an alignment treatment. Moreover, it is necessary to provide an alignment film on the surface of the substrate.

In the present invention, the transparent conductive film 50 is different from the conventional one.
2 is provided independently of the photoconductive layer 504. Then, an insulator 503 is formed between the photoconductive layers to be insulated. A metal reflection film 505 is independently provided on the photoconductive layer and the insulator. With such a structure, a light valve excellent in high-speed response is formed. The ratio of dark resistance to bright resistance of the photoconductive layer is preferably 10 ³ or more. This depends on the light irradiation method. For example, when an image is input to a light valve by a CRT, it is expected that this resistance ratio will be large if the fluorescence emission time of the CRT is short. On the other hand, even CRTs with long fluorescence emission time and liquid crystal displays (LC
In the case of performing the scanning in the line-sequential mode such as D) or the plasma display (PDP), 10 ³ or less may be sufficient.

When light is irradiated while a voltage is applied between the transparent conductive films 502 and 507, the resistance of the photoconductive layer is lowered and the transparent conductive film 507 opposed to the reflective film (also acting as an electrode) 505. Capacitance occurs between them. When the light irradiation is completed, the photoconductive layer has a high resistance, but since a voltage is applied between the transparent conductive layers, the charge accumulated on the reflective film 505 remains.

If the image information is to be cancelled, if the voltage between the transparent conductive films is set to 0, the resistance of the photoconductive layer is not infinite, so the charge on the reflective film 505 gradually decreases. In order to more positively remove charges, light irradiation may be performed on the entire surface while the voltage is 0. Further, if necessary, one of the transparent conductive films may be formed in a stripe shape so that a voltage is independently applied. Responsiveness and
The light valve device has excellent light reflectivity (contrast).

Next, the light valve display device provided by the present invention will be described. In a conventional light valve display device, a light valve corresponding to three colors of RGB has a structure in which light is continuously irradiated. Therefore, the optical device is complicated and effective, as described above. On the other hand, in the present invention, it is proposed that the screen corresponding to each of the RGB colors is temporally divided to be performed on one screen. That is, a red (R) screen is projected at a specific time, a green (G) screen is projected at the next time, and a blue (B) screen is projected at the next time. By repeating this, a color image is visually obtained.

For that purpose, each color laser as a light source and a device (two-dimensional optical switch device) for optically switching by changing the reflectance of light by an electric method such as a light valve are closely connected. We must work together.

A conceptual diagram of the image display device of the present invention is shown in FIG. Although the basic structure of the present invention is shown in FIG. 1, various devices other than the above must be added for actual operation. Hereinafter, the device shown in FIG. 1 will be described for the purpose of explaining the technical idea of the present invention.

First, unlike the prior art, three color laser light sources 110 to 112 are prepared in the present invention. This laser light source is required to generate laser light in a pulsed manner or monochromatic light having parallelism equivalent to that. Therefore, this light source is not limited to a simple laser oscillation device, but may be a device in which a laser oscillation device is combined with a laser amplification device. Further, the laser oscillation device may be combined with a wavelength conversion device such as a non-linear optical device. In this case, coherent light (second harmonic wave, third harmonic wave, and fourth harmonic wave) having a frequency twice, three times, or four times the laser oscillation frequency is extracted. Similarly, it is also possible to extract the sum or difference of the frequencies by synthesizing two laser beams of different wavelengths generated by using one or more laser oscillators by utilizing the nonlinear optical effect. Is.

The extremely highly parallel and thin beam emitted by such a device is reflected by an optical device 10 such as a mirror.
7 to 109 aligns on one axis. The operation of aligning the optical axes is relatively easy. Because at this stage these laser lights do not contain any image information, the light is very parallel and
This is because the beam is also thin. In the conventional light valve display device, the light reflected by the light valve is aligned on one axis, but in that case, the parallelism of the beam is extremely bad because of the diffraction of the light due to the image information and the like. ,
Since the optical axis itself was also large, it was very difficult to align the optical axis.

Then, the optical axis which has become one axis is the optical device 10.
5, the light beam is expanded to an appropriate size. The optical device 105 does not need to use expensive and precise optical equipment as used conventionally, and may be a single lens.
This is because at this stage the beam is already aligned with one axis and its parallelism is no longer needed. Therefore, for example, a lens having extremely large chromatic aberration may be used.

After that, the beam passes through the optical device 102, enters the two-dimensional optical switch device 103 such as a light valve, and is reflected in accordance with the image information displayed by the display device 104 such as a CRT. The light beam containing the reflected image information again enters the optical device 102, is reflected, and is projected on the screen in front. The image may be projected on the screen as in FIG. 1 or may be passed through an optical device for further magnification. In this case, the optical device needs to use a high quality lens with less chromatic aberration and barrel aberration, which is the same as in the case of the conventional projector.

As the display device 104, in addition to the CRT, L
A CD or PDP may be used, and when an LCD is used, an inexpensive simple matrix type may be used instead of the expensive active matrix type. In particular, it is desirable to use a flat panel display such as an LCD or PDP for downsizing the device. Further, since the PDP or the active matrix type LCD can respond at high speed, high quality moving images can be expressed.

When connecting these display devices and the light valve, as shown in FIG. 6 (A), the light valve is brought into close contact with the display screen.
There are two possible methods of forming an image of the displayed image on the light valve by the optical system 604. In the former case, a material such as glass is sandwiched between the display screen and the light valve, but the image may be blurred even though it is said that they are brought into close contact with each other. In the latter case, such a problem is extremely small, but since it uses an optical system, it requires a volume. In the figure, 601a and 601b are light valves, 602
a and 602b mean CRTs, and 603a and 603b mean fluorescent screens of CRTs. Although the case of the CRT is described in FIG. 6, the same applies to an LCD or a PDP.

The light incident on the light valve is TN from the liquid crystal.
In the case of liquid crystal or STN liquid crystal, it is required to be polarized light, and conventionally, polarized light is obtained by using a non-coherent light source and a polarizing plate. However, there is a problem in that the amount of light is extremely reduced when transmitted through the polarizing plate, resulting in a dark screen. However, when a laser is used, if the polarization direction of the laser is aligned in one direction in advance, almost 100% of the light can be transmitted to the polarizing plate of the light valve.

In the present invention, it can be said that the advantage of utilizing a coherent light source such as a laser lies in this part. However, since the dispersion type liquid crystal (also referred to as polymer liquid crystal) that utilizes the scattering of light does not require polarization, it does not change whether it is coherent light or non-coherent light.

Further, since the laser light is an extremely ideal monochromatic light, its expressible (combinable) color is superior to the conventional CRT. The situation is shown in FIG. The triangle that is shown as a laser light valve in the figure
FIG. 2 is a diagram showing a color region that can be displayed according to the present invention, where a He--Ne laser (red), Nd: Y is used as a light source
Second harmonic of AG (green), Ar ⁺ ion laser (blue)
Is used. It can be seen that more versatile display is possible compared to the conventional light valve display device and CRT. In particular, it is excellent in displaying a green color, which is difficult to display in a conventional CRT.

As described above, in the present invention, one sheet of 2
Since the two-dimensional optical switch device is operated in a time-sharing manner to display images of RGB colors, the two-dimensional optical switch device and each laser device must operate in close cooperation.
Therefore, these are connected to the image control device by cables 113 to 116. In the past, only each light valve was connected to this image controller.

Next, the display method according to the present invention will be described. FIG. 2 shows the basic operation of the present invention. In this example, an analog voltage is applied to the light valve.

In the display device 104, each pixel is scanned in the so-called line quasi-order mode in order from the upper row to the lower row, and the pixel A is above the pixel B. The voltage states of the pixels are shown in “pixel A” and “pixel B”, but the details thereof are omitted here. On the other hand, the state of pulse oscillation of the laser is shown by "Laser G" (green emission laser), "Laser B" (blue emission laser), and "Laser R" (red emission laser) in the figure. As is clear from the figure, the lasers emit light in a pulsed manner in order at intervals.

For example, paying attention to the state where the red laser emits light, the period is extremely short. For example, if one frame is 30 msec, the theoretical maximum period is 10 m.
sec, and it is desirable that it is actually 5 msec or less. This limitation arises primarily from display 104 image processing problems and the response speed limitations of the liquid crystal material used in the light valve. Further, in order to ensure display, it is necessary that the image is not rewritten while the laser light is being irradiated. In a sense, it can be said that the laser light irradiation is performed between the rewriting of images.

In order to take out the pulsed laser light, continuous wave laser light may be taken out in a pulsed form by an optical shutter device or may be carried out by exciting the laser in a pulsed form. Alternatively, the oscillation state of the laser may be controlled in a pulsed manner by the Q switch. In the digital gradation method described later, it may be necessary to control the pulse width of the laser. Generally, it is almost impossible to control the pulse width by the pulse excitation or the Q-switch method, so it is preferable to use a mechanical or electrical optical shutter.

In the example of FIG. 2, when the green laser is irradiated, the pixel A is in the voltage state of "4" and the pixel B is
Is in the voltage state of "1". Furthermore, when irradiated by the blue laser, both are in the "2" voltage state.
When irradiated with the red laser, both are in the voltage state of "3". In this way, color display can be performed. In reality, the voltage varies from place to place due to non-uniformity, and the pixel voltage changes over time for various reasons, and these were taken into consideration in order to perform clear gradation display. Correction is necessary.

For example, considering the time from the charging of the pixel to the irradiation of the laser beam, the pixel A in the upper part of the screen has a longer time than the pixel B, and
During that time, since the voltage is continuously applied to the transparent conductive film, the voltage increases greatly when the laser is irradiated. In addition, when the transparent conductive film of the light valve is processed into stripes and the voltage applied to each stripe is applied in synchronization with the line-sequential scanning of the display device, the voltage drops as time elapses. A has a more significant voltage drop than pixel B. For that purpose, it is necessary that the ratio of the dark resistance and the light resistance of the photoconductive layer is sufficiently large. Specifically, a ratio of more than the number of rows is required. For example, 1
For a display of 000 lines, a resistance ratio of 1000 or more is required.

Further, in the example of FIG. 2, the pixel voltage is set to 0 every time the laser light of each color is irradiated. For that purpose, for example, a uniform light beam may be applied to the light valve in a state where the voltage between the transparent conductive films is removed. This is because the light valve having the structure shown in FIG.
This is because there is no other method than to remove the charges accumulated in 5 by natural discharge or by making light incident from the outside again to make the semiconductor region 504 conductive.

Although the gradation display method as described above is called analog gradation, the degree and reliability of gradation display are low in analog gradation, and it is not suitable for various kinds of display as in the present invention. Therefore, an example of display display by a digital gradation method suitable for the present invention will be shown below.

FIG. 3 shows an example of digital 4-gradation display. In FIG. 3 (A), one frame is divided into three, and the first 1/3 is assigned to the red image, the middle 1/3 is assigned to the blue image, and the last 1/3 is assigned to the green image. There is. For example, pixel A has red, blue, and green respectively "4", "1", and "3", and pixel B has respectively
If color display of "2", "3", and "1" is performed, pixel A is irradiated during the first irradiation of the red laser four times.
4 times, and the pixel B may be turned on twice. Similarly, when the blue laser irradiates, the pixel A may be in the ON state once, the pixel B may be in the ON state three times, and when the green laser is in the irradiation, the pixel A may be in the three times and the pixel B may be in the ON state once. In this case, the voltage shown in the figure may be applied. The figure shows that there is a voltage drop due to spontaneous discharge. Also in this case, it is necessary to operate so that the voltage of the pixel becomes 0 with the irradiation of the laser beam.

Regarding such a gradation display method, Japanese Patent Application Nos. 3-157502 and 3-1 which are the inventions of the present inventors.
57603, 3-157604, 3-15760.
5, 3, 3-157606, and 3-157607.

FIG. 3B shows a gradation display method of the same method, but in the same manner, when performing 4-gradation display, laser light irradiation is performed in G, B and R during the first ¼ frame. In the following, there is shown a method of irradiating all of the above, and repeating this three more times. Again, by applying a voltage as shown in the figure, red, blue and green are respectively supplied to the pixel A.
For “4”, “1”, “3”, and pixel B,
Color display of "2", "3", and "1" can be performed.

What must be noted in any of the methods is that the pixel (depending on the image information of the display device) is
That is, the applied voltage does not directly reflect the light transmittance of the pixel. For example, if 16 gradation display is performed at 30 frames / second by the method of FIG. 3, the laser pulse interval is only 2.5 msec. In particular, when a super twisted nematic (STN) liquid crystal or a twisted nematic (TN) liquid crystal, which has a slow response to a voltage, is used, the liquid crystal cannot follow the change in the voltage, as shown by the broken line in the figure. It may show transmission characteristics. In this case, when it is completely unexpected, it will be in the ON state, and, for example, there will be a gradation error and color mixing. In particular, FIG.
When the laser beams are frequently changed and irradiated as in (B), color mixing is intense.

To solve this problem, the driving speed may be lowered until the liquid crystal can follow, or a material having a sufficiently high operating speed such as a ferroelectric liquid crystal or an antiferroelectric liquid crystal may be used. However, a reduction in driving speed means a reduction in gradation and also causes a deterioration in image quality, so the speed cannot be reduced unnecessarily. Also, 1 frame 30 msec
If 64 gradations are to be displayed under the above condition, the pulse interval is 150 μsec, and even the ferroelectric liquid crystal, which boasts the highest speed, can barely follow. Therefore, there is a need for electro-optical materials that respond faster.

Although FIG. 4 also relates to the digital gradation system, it relates to a system other than the above. Here, a plurality of pulse widths or pulse wave heights of the laser to be irradiated are prepared, and the brightness is changed by the combination thereof. In FIG. 4, all 8
An example of gradation display is shown. In FIG. 4 (A), the widths of three consecutive laser pulses gradually increase in order. Further, in FIG. 4B, the wave heights of three consecutive laser pulses gradually double. Thus, for example, in pixel A, G, B, and R are
For “5”, “3”, “2”, and pixel B,
It is possible to perform gradation display of "1", "3", and "6".

Generally, in normal laser operation,
It is not easy to change the pulse width or the pulse height, and therefore, it must be done by adding some device to the laser oscillation device.

For example, a pulse width or a pulse height can be changed by mounting an element whose electrical characteristics are changed electrically inside or outside the laser oscillator.
A liquid crystal can be used as such an element.
However, great care must be taken when including such elements. For example, if such an element is provided inside the laser oscillator (between the resonators) in an attempt to change the pulse width of the laser, the emitted light is not amplified in the opaque state, and laser oscillation does not occur, but it is transparent. In this state, laser oscillation occurs, and once the oscillation starts, the energy increases sharply. For example, it is not uncommon for the gain of laser light to reach 10 or more during one round trip of the resonator. In that case, if the transparency of the optical switch element inside the resonator is not high, a part of the light may be absorbed and burned out.

Therefore, when changing the pulse width of the laser, it is desirable to mount the optical shutter outside the resonator. Further, in such a case, it is difficult to use a laser in pulsed oscillation due to its operating principle, so that it is used in a continuous oscillation (CW) state.
In that case, if the optical shutter is in the OFF state, the laser light becomes heat without being used for the image,
Loss occurs. In order to reduce this loss, it is advisable to make the irradiation time of the laser light longer than the time spent for rewriting an image in the two-dimensional optical switch device.

On the other hand, in the case of changing the pulse height of the laser pulse, it is almost impossible to control it by providing an electro-optical device inside the resonator. Is desired. For example, in the ON state, by providing six electro-optical elements having twice the transmittance as in the OFF state, six stages (1, 1/2, 1/4, 1/8, 1/16, Three
It is possible to adjust the light amount of ½), and as a result, it is possible to display 64 gradations. In this case, a material having relatively low transparency such as liquid crystal can be used. Also,
When the laser is oscillated by a method such as pulse excitation or the Q-switch method, the light emission is used very efficiently except for the portion not used by the electro-optical element.

[0062]

【Example】

[Embodiment 1] An embodiment of the present invention using an Ar ⁺ laser as a blue light source, a second harmonic of an Nd: YAG laser as a green light source, and an emission of a He-Ne laser as a red light source will be described below. .. In FIG. 8, 804 is a discharge tube filled with Ar gas, 805 is a crystal rod of Nd: YAG, and 807 is a He-Ne discharger. KDP, KTP or LiNbO on the extension of Nd: YAG rod
Non-linear optical element 806 such as ₃ is inserted, and Nd: YAG
Second harmonic of lasing laser light of 1.06 μm (532
nm). The non-linear element may be an organic non-linear optical material. Excitation by a krypton arc lamp may be used for excitation of Nd: YAG, but if near-infrared light of a semiconductor laser is used as an excitation light source, it is compact and easy to cool.

Reflecting mirrors are provided at both ends of these light emitting bodies in the long axis direction to form a resonator. Although not shown in the drawing, the side surface of each light emitting body is covered with a reflecting material so as to efficiently reflect the emitted light and perform laser oscillation. Among these mirrors, 801 to 803 are total reflection mirrors, and 811 and 813 are half mirrors. Also, 81
Reference numeral 2 is a material that is totally reflective to infrared light and transparent or translucent to visible light. In the present invention, since it is necessary to oscillate each laser in a pulsed and electrically controlled manner, Pockels cells 808 to 810 are provided inside each resonator to electrically switch. It is structured to do.

With the Ar ⁺ laser, the oscillation wavelength is 476.
There are three types, 5 nm, 488 nm and 514.5 nm. Three
Since the color reproducibility is poor in the state in which the two oscillated lights are mixed, it is desirable to remove light of unnecessary wavelengths. Therefore, although not shown in the figure, a color filter is provided outside the resonator to select output light, or wavelength selectivity is exhibited inside the resonator by an optical interference effect like an etalon. It is desired to eliminate unnecessary wavelength oscillation itself depending on the element.

As described above, the respective color lights output from the three oscillating devices are converted into optical elements 81 such as prisms and half mirrors.
4-817 collects as one ray on one axis. If the Pockels cells in each laser oscillator are turned on at the same time, mixed light of three colors (white light) is output. However, in the present invention, since each Pockels cell is turned on separately, strictly speaking, Will output each color separately. Oscillation light from these laser devices is incident on the light valve as probe light via the optical device.

Example 2 An example of an apparatus for carrying out the present invention using a dye laser is shown in FIG. Also, the mechanism for changing the pulse height of the output pulse by the liquid crystal optical shutter will be described. The dye laser is known as a wavelength tunable laser that oscillates when excited by various ultraviolet lasers, flash lamps, and the like, and it is also extremely useful because it can easily oscillate each color by changing the dye. For example, in the example of Example 1, in order to oscillate each color, some had to perform discharge excitation and some had to perform lamp excitation. However, since the dye laser can oscillate in the same manner from blue to red, the structure of the device is simple. As a pigment, red is rhodamine B (605-
635 nm), green is sodium fluorescein (53
0-560 nm), blue is 7-hydroxycoumarin (45
0-470 nm) may be used. Of course, other various dyes can be used.

When these dyes are excited by light to resonate, a light emission having a considerably broad spectrum is generated, but since it is not sufficient for use in the present invention as it is, a diffraction grating or a prism, A wavelength selection element such as an etalon is inserted to select the oscillation wavelength. When used as a wavelength tunable laser for spectroscopy, a diffraction grating having a narrow oscillation wavelength width and good spectral characteristics is used. However, in the present invention, the oscillation wavelength width may be broader by a factor of 10 or more as compared with such spectroscopy. Furthermore, the oscillation wavelength does not have to be variable, but rather easy maintenance is required.
Etalon is suitable.

In this embodiment, as the excitation light source of the dye laser, a nitrogen laser 90 which can be obtained by a relatively small device can be obtained.
1 was used. A nitrogen laser can normally oscillate ultraviolet light having a pulse width of about 10 nsec and a wavelength of about 330 nm by pulse discharge. Therefore, the timing of pulse discharge is adjusted to the timing of oscillation of each color and further the timing of image processing of the liquid crystal panel. Therefore, the repetition frequency of the nitrogen laser is determined according to the image information. For example, by the method of FIG.
If a display of 30 frames per second and 8 gradations is performed, the oscillation repetition frequency of the nitrogen laser is 270 Hz.
(= 30 frames / second × 3 colors × 3 pulses / color) is required.

As shown in the figure, the dye laser has a dye cell 905, an optical shutter 916 in which an etalon (wavelength selection element) and a Pockels element are combined, a total reflection mirror 915, and a half mirror 914, respectively. The ultraviolet light obtained from the nitrogen laser is processed into an elongated shape by an optical device such as a cylindrical lens (not shown), and the dye lasers 905 (B), 906 (G), 907 ( The dye cell of R) is irradiated. Then, the light output from each dye laser is collected on one axis by the mirrors 908 to 912.

Further, as shown in the lower part of FIG. 9, the laser light aligned on one axis passes through an optical element in which three optical shutters are superposed. A liquid crystal optical shutter may be used for this optical element. However, each optical shutter is required to have a structure that transmits half of the light even when it is in the OFF state. To do this, each optical shutter is finely processed to
A window may be formed in an area of 0%. For example, if the transmitted light amount when all three optical shutters are in the ON state is 1, the transmitted light amount when one shutter is OFF is half, and when the two shutters are OFF. The amount of transmitted light is 1/4. When the three optical shutters are turned off, the amount of transmitted light is 8
It becomes one-third. By varying the light quantity in this way, gradation display as shown in FIG. 4 becomes possible. Then, the laser beam passes through the lens 918 and is applied to the light valve.

In the above cases, the transparency of the optical switch element 917 must be carefully considered. Since the laser beam is a strong pulsed light, if there is a partially opaque portion, the damage due to burning or the like spreads from that portion and spreads over the entire element. Therefore, the strength of the laser (power density or energy density) and the resistance of the optical switching element must be taken into consideration.

For example, when the beam diameter of the laser is 1 mm and the image is enlarged and projected on a screen of 1 m, the energy density of the laser beam is at least 100 times that of a conventional projection display device (beam diameter is 1 cm). If it is a pulse of about 100 nsec, the peak output is 1 of that of a conventional projection display device by irradiating a cw-like light source.
It has a power density of 100 million times.

Therefore, when it is a problem to directly enter such strong light into the optical switch element, an optical system such as a lens is inserted in the preceding stage to lower the energy density of the beam. Good. For example, the beam diameter is 1
When it is expanded 0 times, the energy density is reduced to 1/100. Further, in the present invention, at this stage, the laser light emitted from each laser is aligned on one axis and does not include any image information, so that the operation of aligning the optical axis is extremely easy. The optical system may be simple. For example, in FIG. 9, the order of the lens 918 and the optical switch element 917 may be simply exchanged. However, in that case, since the area of the laser beam with which the optical switch is irradiated is large, it becomes difficult to avoid the defect if the optical switch is defective.

[0074]

As is apparent from the above description, according to the present invention, a completely new light valve projection display device is manufactured. The conventional light valve projection display device has a configuration in which the optical axis is adjusted after adding image information, whereas the light valve projection display device of the present invention is configured after the optical axis is adjusted. Since the image information is added, there is little blurring of the screen,
The feature is that an extremely clear image can be obtained. Moreover, even when the optical axis is displaced due to vibration or temperature cycle, the adjustment is easy, and it is suitable for use in ordinary households. Further, from the technical idea of the present invention, it is obvious that the light valve projection display device according to the present invention may be a front projection type or a rear projection type (rear panel type).

Further, since the light valve projection display device of the present invention uses an ideal monochromatic laser beam, it has excellent color reproducibility and its brightness is strong, so that it can be used in a room of normal brightness. There is nothing wrong with displaying the image.

Further, in the light valve projection display device of the present invention, in addition to the conventional analog gray scale display system, a new digital gray scale system which has not existed in the past can be adopted. It is not inferior to any gradation display method. Further, in the present invention, the purpose is especially for color display, but this gradation display method can be used as a digital gradation display method not only for color images but also for single color display.

As described above, the present invention is an epoch-making invention accompanied by a number of new concepts which the conventional light valve projection display device does not have. Similarly, the light valve shown in the present invention is not only suitable for the display method of the present invention, but also has the flexibility that it can be applied to the conventional light valve projection display. The characteristics are sufficiently improved, and higher quality image quality can be obtained even when used in the same display method as the conventional one.

[Brief description of drawings]

FIG. 1 shows a basic configuration of a projection display device of the present invention.

FIG. 2 shows an example of an analog gradation display system according to the present invention.

FIG. 3 shows an example of a digital gradation display method according to the present invention.

FIG. 4 shows an example of a digital gradation display system according to the present invention.

FIG. 5 shows a cross-sectional structure of a light valve device according to the present invention.

FIG. 6 shows an arrangement example of a light valve device in the present invention.

FIG. 7 shows color reproducibility in various display methods.

FIG. 8 shows an example of an optical system according to the present invention.

FIG. 9 shows an example of an optical system according to the present invention.

FIG. 10 shows an example of a conventional projection display device.

[Explanation of symbols]

101 ... Screen 102, 105 ... Optical device 103 ... Light valve device 104 ... Primary display device (CRT, LCD, PDP)
Etc.) 107, 108, 109 ... Mirror 110, 111, 112 ... Laser device 113, 114, 115, 116 ... Signal cable 117 ... Image control device

Claims (6)

[Claims] 1. An optical system capable of aligning a plurality of laser lights on one axis, a two-dimensional optical switch device, and an image projection screen, and irradiates the laser light on one axis to the optical switch device and reflects the laser light. An image display device characterized by projecting light on a screen. 2. The method according to claim 1, wherein each laser beam is polarized in one direction, and the two-dimensional optical switch device is a liquid crystal matrix device having no polarizing plate on the laser light incident side. Image display device. 3. An image display device having at least one pulsed laser light generator and a reflective two-dimensional optical switch device, wherein each laser light generator and two-dimensional optical switch device is a device for controlling an image. An image display device characterized by being connected. 4. A first transparent conductive film formed on a transparent substrate, a plurality of semiconductor photosensors formed on the transparent conductive film so as to be isolated from each other, and a conductive film connected to the photosensors. A first substrate having: a second substrate on which a second transparent conductive film is formed; a liquid crystal material sandwiched between the first substrate and the first substrate;
A device for irradiating the back surface of the substrate with light having image information, a device for irradiating the back surface of the second substrate with light for a probe, and a first transparent conductive film and a second transparent conductive film. An image display device comprising: a device for applying a voltage therebetween. 5. An image display device having a pulsed laser light generator and a reflection type two-dimensional optical switch device, a process of rewriting an image on the two-dimensional optical switch device, and a pulsed laser after the image rewriting is completed. An image display characterized by having a process of irradiating light, a process of erasing an image on a two-dimensional optical switch device after laser light irradiation, and a process of rewriting an image on the two-dimensional optical switch device thereafter. Method. 6. A light valve optical device comprising a transparent substrate having a transparent conductive material film formed on two surfaces and a liquid crystal material sandwiched by the transparent substrate, wherein a voltage in one direction is applied between the transparent conductive materials. And a step of irradiating a light beam having image information, then a step of irradiating a probe light, and then a light beam having no image information is radiated in a state where the voltage between the transparent conductive material films is removed. An image display method comprising the steps of: