JPH08106074A - Picture projection device - Google Patents

Abstract

PURPOSE: To obtain a single lens type picture projection device capable of obtaining a very bright and high-contrast color projected picture by using plural reflection type spatial optical modulators. CONSTITUTION: This picture projection device is constituted of plural reflection type spatial optical modulators, plural polarizing beam splitters arranged opposite the respective readout surface of the modulators, a light source optical system 4, a projection optical system 7, and a color separation optical system and a color synthesis optical system which have dichroic optical elements respectively. The dichroic optical elements in the color separation optical system and in the color synthesis optical system which separate and synthesize readout light respectively are arranged on the same plane. Therefore, the picture projection device where not only the brightness of the projected picture is made compatible with the contrast of the picture but also the reduction of cost is contrived is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type color image projection apparatus.

[0002]

2. Description of the Related Art In recent years, for the purpose of projecting a color image on a large screen with high brightness, images corresponding to each color of red, green, and blue are written in three reflection type optical writing liquid crystal light valves and each reflection is performed. An image projection apparatus has been developed which reads out an image written with a light flux of a corresponding color from a pattern optical writing liquid crystal light valve and projects a color image on a screen.

First, the structure of a reflective optical writing liquid crystal light valve will be described. There are two types of reflective optical writing liquid crystal light valves, one of which changes the scattering state of light and the other of which changes the polarization state of light in order to display an image. In the following, description will be given focusing on a system that changes the polarization state of light.

FIG. 6 is a sectional view showing the structure of a reflective optical writing liquid crystal light valve. Transparent substrates 101a, 101b such as glass or plastic for sandwiching liquid crystal molecules
Is provided with transparent electrode layers 102a and 102b and alignment film layers 103a and 103b on the surface thereof. Transparent substrate 101
a and 101b are the alignment film layers 103a and 103b,
The liquid crystal layer 104 is sandwiched between the spacers 109 by controlling the gap through the spacers 109. Further, a photoconductive layer 105, a light shielding layer 106, and a dielectric mirror 107 are laminated and formed on the transparent electrode layer 102a on the writing side by light between the alignment film layer 103a and the transparent substrate 101a on the writing side. Non-reflective coating layers 108a and 108b are formed on the cell outer surface of the transparent substrate 101b on the side. Liquid crystal layer 1
As the liquid crystal 04, nematic liquid crystal or ferroelectric liquid crystal is used. In particular, a reflective liquid crystal light valve using a ferroelectric liquid crystal has an extremely high operating speed of several hundred Hz or more. A reflective optical writing liquid crystal light valve using a ferroelectric liquid crystal is known as a device that processes an input image by thresholding and binarizes it. Is also known to be possible.

FIG. 7 is a block diagram of an image projection apparatus using a conventional reflective optical writing liquid crystal light valve. In particular, the case of a monocular type with one projection lens is shown. Light source 2
The white light emitted from the light source 05 is efficiently radiated forward using a reflector 206 arranged behind the light source 205, and converted into a substantially parallel light flux by the condenser lens 204. This light beam is polarized beam splitter 203
When incident on, only the s-polarized component is reflected and enters the dichroic prism 202. By the dichroic prism 202 in which the red reflecting surface 209R and the blue reflecting surface 209B are combined in a cross shape, the light flux having only the s-polarized component is separated into three primary colors of red, green and blue. Each of the color-separated light fluxes is a reflection type optical writing liquid crystal light valve 201R, 201G, 2 on which an image for each color is displayed.
The reading surface of 01B is illuminated as reading light. Then, each reflective optical writing liquid crystal light valve 201R, 201G, 20
The reading light reflected by 1B is again incident on the dichroic prism 202 to be color-synthesized, and then is incident on the polarization beam splitter 203. This polarization beam splitter 2
In 03, only the p-polarized light component of the color-combined light flux is transmitted and displayed as a color image on the display screen 208 by the projection lens 207.

[0006]

However, the conventional image projection apparatus has the following problems. (1) Since a perfectly parallel light beam cannot be obtained, the extinction ratio of the polarization beam splitter 203 becomes poor, and a projected image with good contrast cannot be obtained.

Usually, the light flux obtained by the condenser lens 204 is substantially parallel, but it is not perfectly parallel light. Therefore, not only a light beam that enters the polarization splitting surface 210 of the polarization beam splitter 203 at a predetermined angle (usually 45 degrees in most cases) but also a light beam that enters at an angle deviating from the predetermined angle. The polarization beam splitter 203 can obtain a very good extinction ratio for a light beam incident on the polarization splitting surface 210 at a predetermined angle. However, the extinction ratio deteriorates as the incident angle deviates from a predetermined angle with respect to the luminous flux that deviates from that angle. As a result, the contrast of the image projected on the display screen 208 is reduced.

(2) On the contrary, if the contrast is improved,
No bright projected image can be obtained. Contrary to the above (1), in order to improve the contrast of the projected image, the polarization splitting surface 21 of the polarization beam splitter 203 is as much as possible.
It is necessary to make a light beam enter at a predetermined angle with respect to zero.
For that purpose, it is necessary to bring the light beam incident on the polarization beam splitter 203 closer to a parallel light beam. But,
The only way to make the light flux closer to a parallel light beam is to use a pinhole for the light source 205 having a finite size so as to make the size of the light source apparently smaller. As a result, the light amount of the parallel light flux decreases, and a bright projected image cannot be obtained on the display screen 208.

As described in (1) and (2) above, there is a trade-off relationship between the brightness of the projected image and the contrast, and it has been extremely difficult to achieve both at the same time. Therefore,
An object of the present invention is to solve the above-mentioned conventional problems, by making the brightness and contrast of a projected image compatible with each other.
Moreover, it is to obtain an inexpensive image projection device.

[0010]

In order to solve the above-mentioned problems, in the first configuration of the present invention, a plurality of reflective spatial light modulators for displaying an image by changing the polarization state, and each of the reflective spatial light modulators are provided. A polarizing beam splitter arranged to face the reading surface of the reflective spatial light modulator, a light source optical system having a white light source for illuminating the reading surface of the reflective spatial light modulator, and the reflective spatial light modulation. A plurality of reading lights having a wavelength characteristic corresponding to the reflective spatial light modulator, which has a projection optical system for projecting an image displayed on the display and a dichroic optical element, and emits white light emitted from the light source optical system. And a color combining optical system that has a dichroic optical element and combines again the plurality of the reading lights reflected by the reflective spatial light modulator, and separates and combines the reading lights. Yes, the above color separation A dichroic optical element in the academic system and a dichroic optical element in the color synthesizing optical system is disposed in the same plane.

In the second configuration, in the first configuration, the dichroic optical elements in the same plane in the color separation optical system and the color combining optical system are shared. Further, in the third configuration, in the first configuration, a plurality of dichroic optical elements in the color separation optical system and the color synthesis optical system are integrated.

As a fourth structure, the above 1 to 3
In the configuration, the reflective spatial light modulator uses liquid crystal as a light modulation material.

[0013]

For the sake of simplicity, the case of a color image projection device that divides white light into three primary colors will be described below. In the first configuration, a polarization beam splitter optimized for each corresponding color of red (R), green (G), and blue (B) is used as a reading surface of a reflective optical writing liquid crystal light valve corresponding to each color. It is provided facing to. In this case, the wavelength at which each polarization beam splitter should achieve a predetermined performance is 300n as in the conventional case.
It is not the entire visible light range with a range of about m, but at most 10
Only in the range of about 0 nm.

The performance (especially extinction ratio) of the polarization beam splitter largely depends on the degree to which the angle of the light beam incident on the polarization splitting surface deviates from a predetermined angle and the wavelength range of the incident light beam. For example, the extinction ratio becomes better as the wavelength range of the incident light beam such as a laser becomes narrower or the angle of the light beam incident on the polarization splitting surface becomes closer to a predetermined angle.

In the present invention, the wavelength range incident on each polarization beam splitter is narrowed to about one-third of that in the conventional case, so that the angle of the light beam incident on the polarization splitting surface deviates from the predetermined angle. The extinction ratio can be improved. This means that the contrast is improved in the projected image having the same brightness as the conventional one.

Conversely, when the extinction ratio equivalent to the conventional one is sufficient, the angle of the light beam incident on the polarization splitting surface is
It may be further away from the predetermined angle than in the past. That is,
By increasing the amount of light, it is possible to obtain a projected image having the same contrast and improved brightness as in the conventional case, even if the light beam incident on the polarization beam splitter is not as parallel as the conventional case.

Furthermore, by disposing the dichroic mirrors used for color separation and color combination in the same plane,
Can be held by the same machine parts. As a result, not only the number of mechanical parts is reduced, but also the number of adjustment points is reduced, so that the cost can be reduced. Also, in the second configuration, since one that uses separate dichroic mirrors for color separation and color composition is shared, the number of optical components and the mechanical components that hold them are reduced compared to the first configuration, and the cost is further reduced. Down is possible.

In the third structure, for example, two dichroic mirrors can be combined in a cross shape to form a dichroic prism so that they can be integrated. Therefore, the number of optical parts and the mechanical parts for holding them can be different from those in the first structure. Also, the cost can be reduced.

From the above, the brightness of the image projected on the display screen and the contrast of the image can be compatible with each other. In addition, it is possible to reduce the cost by reducing the number of optical components and mechanical components that hold them.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment FIG. 1 is a configuration diagram of a first embodiment of the image projection apparatus of the present invention. The first embodiment of the present invention has a configuration in which different dichroic mirrors are used as color separation and color combining optical systems.

The light source optical system 4 is not strictly described, but may be any optical system capable of generating white light and a substantially parallel light beam. As an example thereof, as described in the prior art, it is possible to use a light source, a reflector and a condenser lens. Examples of the light source that emits white light include a xenon lamp, a metal halide lamp, and a halogen lamp. As the reflector, a hyperboloidal mirror or an ellipsoidal mirror is used. Here, when a hyperboloidal mirror is used, a condenser lens is not necessary.

The light flux emitted from the light source optical system 4 enters the red separation dichroic mirror 8R1 and the blue reflection dichroic mirror 8B1 which are color separation optical systems in this order. Normally, the red reflection dichroic mirror 8R1 and the blue reflection dichroic mirror 8B1 are arranged at an angle of 45 degrees with respect to the incident optical axis. However, needless to say, the angle need not be 45 degrees, and may be changed according to the arrangement of the optical system as long as the dichroic mirror is designed at an angle used. First, the red component in the red reflection dichroic mirror 8R1 is changed to the blue reflection dichroic mirror 8R1.
The blue component is reflected at B1, and the remaining green component is transmitted. As a result, the white luminous flux is separated into three colors of red (R), green (G), and blue (B).

The light beams separated into RGB are reflected by mirrors 5R, 5G and 5B, respectively, and then enter polarization beam splitters 3R, 3G and 3B designed for each color. Here, only the s-polarized light component of each of the RGB light fluxes is reflected, and the reading surface of the reflective optical writing liquid crystal light valves 1R, 1G, 1B for each color is illuminated as reading light.

Reflective optical writing liquid crystal light valve 1R, 1
G and 1B have the structure shown in FIG. 6, liquid crystal is used as the light modulation material, and a spatial light modulator that displays an image by changing the polarization state is used. And FIG.
Although not shown, an image prepared for each color is projected by projecting an image displayed on a CRT or a liquid crystal television on the writing surface of the reflective optical writing liquid crystal light valve 1R, 1G, 1B for each color. Is given. By this, s
The reading light that is incident as polarized light changes its polarization state according to the image given to the writing surface and is reflected.

From the above, the image for each color can be read out from the reflective optical writing liquid crystal light valves 1R, 1G and 1B. At this point in time, since the read image is only phase-modulated, the intensity-modulated image can be obtained by transmitting only the p-polarized component by each polarization beam splitter 3R, 3G, 3B. .

Then, this image is incident on the red reflection dichroic mirror 8R2 and the blue reflection dichroic mirror 8B2 which are color combining optical systems. Here, the red reflection dichroic mirror 8R2 is the red reflection dichroic mirror 8R1.
Are located in the same plane as. The same applies to the blue reflection dichroic mirrors 8B2 and 8B1. And
The blue reflection dichroic mirror 8B2 receives the reading light reflected by the blue and green reflection type optical writing liquid crystal light valves 1G and 1B, and the red reflection dichroic mirror 8R2 receives the red reflection type optical writing liquid crystal. The reading light reflected by the light valve 1R enters. The direction of incidence of each readout light is opposite to that of the readout light separated by the color separation optical system. as a result,
In the reverse process of separating the light flux of white light into each RGB,
The RGB images are combined.

The combined image is incident on the projection lens 7 which is a projection optical system, and a color image can be projected on the display screen. Here, it goes without saying that each reflective optical writing liquid crystal light valve 1R, 1G, 1B is arranged at a position where an image is formed on the display screen by the projection lens 7. Further, it is assumed that the images prepared for each RGB are aligned in advance.

In the above configuration, the wavelengths at which the respective polarization beam splitters 3R, 3G, 3B should fulfill the predetermined performance are in the range of about 300 nm as in the case of using one polarization beam splitter described in the prior art. Not in the entire visible light range, but in the range of at most about 100 nm of each RGB.

When the design value of the incident angle of the polarization beam splitter is 45 degrees with respect to the polarization splitting surface, the width of the incident angle at which the extinction ratio is 100 or more over the entire visible light range is about ± 2.
Up to ~ 3 degrees. However, the wavelength range used is 100
In the case of designing with a limit of about nm, the width of the incident angle at which an extinction ratio of 100 or more is obtained is about ± 3 to 4 degrees, which is considerably wide. In other words, by increasing the amount of light,
Even if the light beam incident on the polarization beam splitter is not as parallel as the conventional light beam, it is possible to obtain the same degree of contrast as the conventional one.

On the contrary, if the amount of light is the same as the conventional one and the width of the incident angle is about ± 2 to 3 degrees, an extinction ratio of about 200 or more can be obtained. As a result, it is possible to obtain a projected image having a higher contrast than the conventional one on the display screen. Further, FIG. 2 shows an example of the spectral transmittance of the blue reflection dichroic mirror. As can be seen from FIG. 2, the wavelength range in which normal p-polarized light and s-polarized light are transmitted is deviated by about 30 to 40 nm. In the reflective optical writing liquid crystal light valve, all of the read light that is incident with s-polarized light is converted into p-polarized light and reflected, and the brightest image is obtained when the display screen is illuminated.
(Conversely, it may be incident with p-polarized light and reflected with s-polarized light.) However, in the conventional case, a portion where the transmittances of p-polarized light and s-polarized light are deviated does not contribute to display. Therefore, if the spectral transmittance of the blue reflection dichroic mirror 8B1 for s-polarized light and the spectral transmittance of 8B2 for p-polarized light are set to be substantially equal to each other, the efficiency becomes very high and a bright projected image can be obtained. Red reflection dichroic mirror 8R1, 8R2
The same applies to.

From the above, it was difficult in the past.
The brightness and the contrast of the image projected on the display screen can be compatible with each other. Moreover, by arranging the red reflection dichroic mirrors 8R1 and 8R2 and the blue reflection dichroic mirrors 8B1 and 8B2 in the same plane, they can be held by the same mechanical component. As a result, not only the number of mechanical parts is reduced, but also the number of adjustment points requiring complicated optical axis adjustment is reduced, which enables cost reduction.

In this embodiment, red reflection dichroic mirrors 8R1 and 8R2 are used. However, considering the layout of the entire optical system, the light source optical system 4 or the projection lens 7 may be replaced by the red reflection dichroic mirrors 8R1 and 8R8.
It goes without saying that a red transmissive dichroic mirror can be used by disposing it in the direction opposite to the reflective optical writing liquid crystal light valve 1R with respect to R2. Similarly, for the blue reflection dichroic mirrors 8B1 and 8B2, a blue transmission dichroic mirror can be used by changing the arrangement of the optical system.

(2) Second Embodiment FIG. 3 is a block diagram of the second embodiment of the image projection apparatus of the present invention. The second embodiment of the present invention has a configuration in which a common dichroic mirror is used in the color separation optical system and the color synthesis optical system. Other than that, the description is omitted because it is the same as the first embodiment.

The red reflection dichroic mirrors 8R1 and 8R2 that are on the same plane in FIG. 1 are commonly used as one red reflection dichroic mirror 6R in FIG. The same applies to the blue reflection dichroic mirror 6B. As a result, this is the first function of the optical system.
This is the same as the embodiment, but the number of optical components and mechanical components can be reduced, so that the cost can be reduced. Further, in the first embodiment, by using different dichroic mirrors for the color combining optical system and the color separating optical system, p
The loss due to the difference between the spectral transmittances of the polarized light and the s-polarized light was covered. However, in the present embodiment, the same thing can be performed by shifting the spectral transmittance between the upper half and the lower half of one dichroic mirror.

Therefore, also in the second embodiment, as in the first embodiment, it is possible to obtain a projected image in which both contrast and brightness are compatible, and it is possible to reduce the cost. (3) Third Embodiment FIG. 4 is a configuration diagram of a third embodiment of the image projection apparatus of the present invention. The third embodiment of the present invention has a configuration in which dichroic prisms are used as the color separation optical system and the color combining optical system. Other than that, the description is omitted because it is the same as the first and second embodiments.

The light beam emitted from the light source optical system 4 first enters the dichroic prism 2. The dichroic prism 2 is obtained by combining the red reflection dichroic mirror and the blue reflection dichroic mirror in the first and second embodiments in a cross shape and integrating them into a prism shape. Needless to say, instead of the prism shape, the mirror shape may be integrated. Further, either the color synthesizing optical system or the color separating optical system may be integrated.

The red light component incident on the dichroic prism 2 is reflected by the red reflection surface 9R, the red component is reflected by the blue reflection surface 9B, and the remaining green component is transmitted, whereby red (R) and green ( G) and blue (B) are separated. In addition, reflective optical writing liquid crystal light valves 1R, 1
When the read lights reflected by G and 1B are incident on the dichroic prism 2 again, the RGB images are combined in the reverse process of separating the white light flux into the RGB.

By the way, the light source optical system 4 radiates a substantially parallel light beam, but a perfect parallel light beam cannot be obtained. Therefore, the distance from the light source optical system 4 to the reflective optical writing liquid crystal light valves 1R, 1G, and 1B (illumination system optical path length)
Also, as the distance (lens back) from the reflective optical writing liquid crystal light valves 1R, 1G, 1B to the projection lens 7 becomes longer, the light flux diffuses and the light amount loss increases.
However, in the present invention, both the optical path length of the illumination system and the lens back are shorter than those in the first and second embodiments, so that the loss of the light amount due to the diffusion of the light flux is reduced.
Therefore, a very bright image can be obtained.

Further, the dichroic prism 2 in which the red-reflecting and blue-reflecting dichroic mirrors are combined in a cross shape and integrated, the number of optical components and mechanical components is further reduced as compared with the second embodiment. Therefore, the cost required for adjusting the optical axis can be greatly reduced.

Therefore, also in the third embodiment, similarly to the first and second embodiments, it is possible to obtain a projected image in which both contrast and brightness are compatible, and it is possible to reduce the cost. The content described above is an example in which a reflective optical writing liquid crystal light valve is used as the reflective spatial light modulator.
Crystal (Bi ₁₂ SiO ₂₀ ) and lithium niobate (LiNbO)
Needless to say, such as may be used.

Although not shown, a writing element such as a CRT or a liquid crystal television is used as a means for writing an image in the reflective spatial light modulator, and the image is displayed on the writing surface of the reflective spatial light modulator. It goes without saying that a configuration in which the writing element and the reflective spatial light modulator are integrated by using a fiber plate or the like may be used other than the method of forming an image.

In the above embodiment, only the s-polarized light component reflected by the polarization beam splitter is radiated as the read light to the read surface of the reflective spatial light modulator, and the read light that has entered the polarization beam splitter again is transmitted. The display screen was irradiated with only the p-polarized light component. However,
The reverse configuration is also possible. FIG. 5 shows a configuration example of another arrangement of the reflective spatial light modulator. In this figure, only the part of the reflective spatial light modulator for green 1G is focused, but the same applies to the reflective spatial light modulators corresponding to other colors. Only the p-polarized light component transmitted through the polarization beam splitter 3G is applied to the read surface of the reflective spatial light modulator 1G as read light, and only the s-polarized light component reflected by the polarization beam splitter 3G among the reflected read light is displayed on the display screen. Needless to say, the configuration may be such that the image is projected onto.

Further, in the above embodiment, only the s-polarized light of the read light is used by the polarization beam splitter. However, as shown in FIG. It goes without saying that a brighter projected image may be obtained by arranging a reflective spatial light modulator for the polarization component and using two reflective spatial light modulators for each color. Yes.

In the above embodiment, white light is separated into three primary colors of red, green and blue, but it goes without saying that two or four or more colors may be used if there are a plurality of separated colors.
Further, in the above embodiment, the red reflection dichroic mirror and the blue reflection dichroic mirror are arranged in this order when viewed from the light source optical system 4, but it goes without saying that they may be arranged in the reverse order.

[0045]

As described above, it is possible to obtain an image projection apparatus which can reduce the cost as well as make the brightness and the contrast of the image projected on the display screen compatible with each other.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of an image projection apparatus according to the present invention.

FIG. 2 is a diagram showing an example of a spectral transmittance of a blue reflection dichroic mirror.

FIG. 3 is a configuration diagram of a second embodiment of the image projection apparatus according to the present invention.

FIG. 4 is a configuration diagram of a third embodiment of the image projection apparatus according to the present invention.

FIG. 5 is a configuration diagram of another arrangement of the reflective spatial light modulator according to the present invention.

FIG. 6 is a cross-sectional view showing the structure of a reflective optical writing liquid crystal light valve.

FIG. 7 is a configuration diagram of a conventional image projection device.

[Explanation of symbols]

1R, 1G, 1B reflective optical writing liquid crystal light valve 2 dichroic prism 3R, 3G, 3B polarizing beam splitter 4 light source optical system 5R, 5G, 5B mirror 6R red reflective dichroic mirror 6B blue reflective dichroic mirror 7 projection lens 8R1, 8R2 Red reflection dichroic mirror 8B1, 8B2 Blue reflection dichroic mirror 9R Red reflection surface 9B Blue reflection surface 101a, 101b Transparent substrate 102a, 102b Transparent electrode layer 103a, 103b Alignment film layer 104 Liquid crystal layer 105 Photoconductive layer 106 Light-shielding layer 107 Dielectric mirror 108a, 108b Non-reflective coating layer 109 Spacers 201R, 201G, 201B Reflective optical writing liquid crystal light valve 202 Dichroic prism 203 Polarizing beam splitter 204 Condenser Lens 205 Light source 206 Reflector 207 Projection lens 208 Display screen 209R Red reflective surface 209B Blue reflective surface 210 Polarized light separating surface

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Iwaki 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronics Industry Co., Ltd.

Claims (4)

[Claims] 1. A plurality of reflective spatial light modulators for displaying an image by changing the polarization state, and a polarizing beam splitter arranged so as to face the reading surface of each of the reflective spatial light modulators. A light source optical system having a white light source for illuminating the reading surface of the reflective spatial light modulator, a projection optical system for projecting an image displayed on the reflective spatial light modulator, and a dichroic optical element, A color separation optical system that separates white light emitted from the light source optical system into a plurality of readout lights having wavelength characteristics corresponding to the reflection type spatial light modulator, and a dichroic optical element, and the reflection type spatial light. A color combining optical system that combines again the plurality of the reading lights reflected by the modulator, and separates and combines the respective reading lights; a dichroic optical element in the color separating optical system; and a color combining optical system in the color combining optical system. Dichro An image projection apparatus characterized in that it is in the same plane as the optical element. 2. The image projection apparatus according to claim 1, wherein the color separation optical system and the color combination optical system have common dichroic optical elements in the same plane. 3. The image projection apparatus according to claim 1, wherein a plurality of dichroic optical elements in the color separation optical system and the color combination optical system are integrated. 4. An image projection apparatus, wherein the reflective spatial light modulator according to claim 1 uses liquid crystal as a light modulation material.