JPH0659235A - Projection type display device - Google Patents

Abstract

PURPOSE:To obtain the projection type liquid crystal display device which can effectively utilize light emitted by a light source. CONSTITUTION:The projection type display device is equipped with a polarizer including a polarization beam splitter 6 through which the light beam flux emitted by the light source 3 is transmitted and uses the S- or P-polarized light component of the light beam flux as projection light, and has a polarizing filter 20 which is arranged between the light source 3 and polarizing element on the center optical axis of the light beam flux and composed of a polarizing plate formed in a convex shape toward the polarizing element slantingly and symmetrically about the center optical axis so that the light beam flux is made incident at a 45 deg. incidence angle and a phase plate 21 which is arranged between the light source 3 and a polarizing filter 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a polarizing element such as a polarizing filter, a polarizing plate or a polarizing beam splitter through which a light beam emitted from a light source is transmitted.
The present invention relates to a projection type display device having a projection optical system that uses a polarization component as projection light.

[0002]

2. Description of the Related Art An example of such a projection type display device is a liquid crystal display device using a photoconductive type liquid crystal light valve (LCLV element) or the like. Such a photoconductive liquid crystal light valve is of a reflective type in which a reflective layer or the like is provided between the liquid crystal layer and the photoconductive layer. FIG. 1 shows an example of the configuration of such a reflection type projection type liquid crystal display device. In the figure, the photoconductive layer side of the photoconductive liquid crystal light valve 1 is coupled to the front face of the CRT 2. The CRT writes the image displayed on its front face to the photoconductive layer of a conductive liquid crystal light valve through the optical fiber layer. The grayscale of the projected image of the liquid crystal layer is formed according to the potential of the photoconductive layer. On the other hand, the luminous flux emitted from the light source 3 such as a metal halide lamp is incident on the polarization beam splitter 6 via the cold mirror 4, the condenser lens 5, the optical elements such as the polarizing plate 7, and the like.
The P-polarized component of this incident light passes through the polarization beam splitter 6. The S-polarized component is the polarization beam splitter 6
Then, the traveling direction is bent and enters the photoconductive liquid crystal light valve 1.

Here, when a projected image is drawn on the liquid crystal layer of the photoconductive liquid crystal light valve 1, the reflected light reflected by the photoconductive liquid crystal light valve 1 depends on the light and shade of the image of the liquid crystal layer. The P-polarized component will be locally included.
Then, only the P-polarized component in the reflected light passes through the polarization beam splitter 6 as it is, so that the image of the P-polarized component is projected on the screen 9 through the projection lens 8.

As described above, the optical elements such as the polarization beam splitter 6 and the polarizing plate 7 are arranged downstream of the high-luminance light source such as the metal halide lamp 3 in the housing of these projection type display devices. Complete polarization separation of the polarization beam splitter is impossible, and in the polarization beam splitters for all wavelengths, at least 2 to 5% or more of leaked light, that is, unpolarized extra light reaches the downstream optical system, Changes to heat. In order to increase the degree of polarization, the polarizing plate 7 is provided with the polarizing plate 7 upstream of the polarizing beam splitter 6 and is attached to the polarizing beam splitter having a large heat capacity as a measure against heat.

[0005]

However, since optical elements such as a polarizing plate and a polarizing beam splitter have a high light absorptivity and a temperature performance limit, they cannot be used at high temperatures. Further, in the projection type display device using the photoconductive type liquid crystal light valve, the leaked light causes deterioration of resolution and contrast.

It is an object of the present invention to provide a projection type liquid crystal display device which can effectively utilize the light emitted from the light source.

[0007]

A projection type display device of the present invention comprises a polarizing element including a polarizing beam splitter through which a light beam emitted from a light source passes, and an S or P polarization component in the light beam is projected onto a projection light. A projection type display device used as, arranged between the light source and the polarizing element on the central optical axis of the light flux, inclined symmetrically with respect to the central optical axis, and convex toward the polarizing element. It is characterized in that it has a polarizing filter formed of a polarizing plate having a shape and in which the light beam is incident at an incident angle of 45 degrees, and a phase plate arranged between the light source and the polarizing filter.

[0008]

According to the present invention, not only the light emitted from the light source can be effectively utilized, but also the leakage light to the polarization beam splitter can be effectively removed and the cooling of the optical element such as the polarization beam splitter or the polarizing plate can be promoted. it can.

[0009]

FIG. 2 shows a projection type display device according to an embodiment of the present invention. This projection display device has a polarization filter 20 disposed between a light source 3 and a polarization beam splitter 6 that receives light emitted from the light source, and near the light receiving surface. The polarization filter 20 is a pair of polarizing plates that are symmetrical with respect to the central optical axis of the incident light beam and are inclined at about 45 degrees, and have a convex shape 20b toward the polarizing beam splitter. Further, this projection display device has a phase plate 21 arranged between the light source 3 and the polarization filter 20. Other components in this display device are the same as those shown in the same reference numerals in FIG. A polarizing plate 7 arranged further near the light receiving surface of the polarization beam splitter 6 is provided to increase the degree of polarization. Since the degree of polarization is increased upstream of the polarization beam splitter 6 in order to use the desired P-polarized component as the projection light in this way, the polarization filter 20 is also called a prepolarizer.

As shown in FIG. 3, such a polarization filter 2
The zero polarizing plate 20b has, for example, a shape having an inclined light receiving surface symmetrical with respect to a plane including the central optical axis of the incident light beam. This can be formed by adhering two rectangular polarizing plates in the plane at each one edge portion thereof. Thus, the polarizing plate 20b is installed on the light source side of the light receiving surface of the polarization beam splitter 6, that is, on the light incident side.

The polarizing plate 20b is, for example, as shown in FIG. 4, a glass flat plate 10 and a polarizing film 1 formed on both surfaces thereof.
It consists of 1. The polarizing film 11 having a predetermined thickness has a refractive index of 2.
TiO ₂ , ZnS, and ZrO _{2 that} are as high as 25 are used. The polarizing film 11 is a pair of layers each having the same film thickness d, and n
> Ng (n = refractive index of the polarizing film 11, ng = glass flat plate 1
(Refractive index of 0) and n · d≈550 / 4 nm. Polarizing films 11 on both sides of the glass plate 10
Was formed in order to increase the degree of polarization.

Here, in the case of the polarizing plate 20b made of a glass flat plate having two rectangular polarizing films, in the projection type display device, air is sent from above or below the drawing of the polarizing plate 20b shown in FIG. The polarizing plate 20b can be cooled by arranging a blowing means such as a fan or an air passage. In the present embodiment, as shown in FIG. 5, the polarizing plate 20b of the polarizing filter 20 has a shape that is open toward the light source 3, that is, convex toward the polarizing beam splitter 6, and is 45 with respect to the optical axis.
The polarizing plate 20b is inclined. In this embodiment,
Light source 3 such as metal halide lamp and pre-polarizer 20
A transparent body that gives a phase difference, that is, a phase plate 21 is installed. The phase plate 21 is, for example, a quarter wave plate. Further, the phase plate 21 may be a liquid crystal shutter using a liquid crystal that emits light. In this embodiment, linearly polarized light is made incident on the quarter-wave plate 21 at an angle θ = 45 ° (the angle formed by the vibration direction of the electric field vector of the incident light of linearly polarized light and the main cross section of the quarter-wave plate). In this case, if the angle θ is −45 °, the emitted light beam becomes circularly polarized light in the reverse rotation, and if the direction of propagation is reversed, that is, if the circularly polarized light beam is incident on the ¼ wavelength plate, The emitted light is converted into linearly polarized light.

Therefore, in FIG. 5, the natural light emitted from the metal halide lamp light source 3 becomes substantially parallel light by the rear reflector 32 and travels downstream. After that, the light passes through the λ / 4 wave plate 21 and reaches the prepolarizer 20. In the prepolarizer 20, due to the above-mentioned action, the polarized light is separated, and a large amount of effective P-polarized light is transmitted to the optical system, and goes to the downstream optical system as it is. On the other hand, the unnecessary P-polarized component is the polarizing plate 20 of the prepolarizer 20 as shown in the figure.
It is reflected twice at b and returns to the light source again. The P-polarized component light passes through the quarter-wave plate and is given a phase difference of π / 2 to be circularly or elliptically polarized light.

The returning light is condensed and returned by the reflector 32 to the linear light source of the metal halide lamp 3, and the reflecting film 33 provided near the linear light source of the metal halide lamp 3.
Is reflected again, and passes from the reflector 32 and again through the quarter-wave plate 21. Here, the phase difference of π / 2 is given again,
This ray has a shape in which the initial vibration direction can be bent by 90 °. As a result, the P-polarized light component cut by the prepolarizer 20 is initially effective.

In this way, the incident angle of the light beam on the polarizing plate 20b of the prepolarizer 20 is set to be near 45 °,
The shape of the polarizing plate 20b is preferably inclined by 45 ° with respect to the central optical axis opened toward the light source 3. As a result, the polarization characteristic is also good, and the ray of the P-polarized component returns to the reflector 32 faithfully. As a result of the experiment, the incident angle of the polarizing plate 20b was set to 4
Even when the angle is changed to 40 ° and 50 ° in addition to 5 °, FIG.
As shown in (1), the reflectance of the unnecessary S-polarized light in the partially polarized light was as high as about 80%, and the favorable reflectance of the P-polarized light to be transmitted was several% or less. As described above, the difference between the reflectance of P-polarized light and the reflectance of S-polarized light in the obtained partial polarized light is large, and the S-polarized light can be used again as the projection light.

In the prepolarizer 20, the polarizing plate 20
When the incident angle of the light beam on b is 45 °, the polarizing plate 20
It is preferable that the surrounding of b is not filled with air having a low refractive index, and the liquid 20a having a refractive index of n = 1.5 is filled in the transparent casing surrounding the polarizing plate 20b to surround the polarizing plate 20b. This is to improve the polarization characteristics. Also, the polarizing plate 20
This is because b can be cooled.

FIG. 7 specifically shows a projection type display device using three CRTs that emit RGB (red, green and blue) light. The apparatus includes R, G, and G CRTs 2 and LCs corresponding to the respective CRTs 2.
LV element 1, total reflection mirror M, G reflection mirror MG, B reflection mirror MB, liquid polarization prism 6, zoom lens 8,
A polarizing plate 7, a prepolarizer 20, a retardation plate 21, an IR cut filter 31, a reflector 32, and a metal halide lamp 3 are provided.

[0018]

According to the present invention, there is provided a projection type display device comprising a polarizing element including a polarizing beam splitter through which a light beam emitted from a light source is transmitted, and an S or P polarization component in the light beam is used as projection light. Polarized light which is arranged between the light source on the central optical axis of the light bundle and the polarizing element, is inclined symmetrically with respect to the central optical axis and has a convex shape toward the polarizing element, and the light bundle is incident at an incident angle of 45 degrees. A polarization filter made of a plate, a phase plate arranged between the light source and the polarization filter,
Therefore, not only the light emitted from the light source can be effectively used but also the polarizing element can be cooled.

[Brief description of drawings]

FIG. 1 is a schematic view of a reflective projection type liquid crystal display device.

FIG. 2 is a schematic view of a reflective projection type liquid crystal display device of the present embodiment.

FIG. 3 is a perspective view of a polarization filter having a polarization beam splitter and a polarizing plate that is symmetrically inclined by 45 degrees with respect to a central optical axis of an incident light beam in a projection display device.

FIG. 4 is an enlarged partial sectional view of a polarizing plate.

FIG. 5 is a schematic view showing a state of an incident light flux on a polarizing filter and a polarizing plate having a light receiving surface inclined with respect to the central optical axis in the present embodiment.

FIG. 6 is a graph showing characteristics of reflectance with respect to an incident wavelength of the polarization filter according to the present invention.

FIG. 7 is a schematic perspective view of a projection type liquid crystal display device of this embodiment.

[Explanation of symbols for main parts]

 1 Photoconductive Liquid Crystal Light Valve 2 CRT 3 Metal Halide Lamp 4 Cold Mirror 5 Condenser Lens 7 Polarizing Plate 6 Polarizing Beam Splitter 8 Projection Lens 9 Screen 20 Polarizing Filter 21 Phase Difference Plate

Claims (3)

[Claims] 1. A projection type display device comprising a polarizing element including a polarizing beam splitter through which a light beam emitted from a light source passes, wherein the S or P polarization component in the light beam is used as projection light. Is disposed between the light source and the polarizing element on the central optical axis of the optical element, is symmetrically inclined with respect to the central optical axis, has a convex shape toward the polarizing element, and the ray bundle is incident at an incident angle of 45 degrees. And a phase plate arranged between the light source and the polarizing filter. 2. The projection type display device according to claim 1, wherein the periphery of the polarizing plate is filled with a liquid. 3. The projection type display device according to claim 1, wherein the polarizing plate is formed by forming polarizing films on both surfaces of a glass plate.