JPH0534672A - Projection type displaying device - Google Patents

Abstract

PURPOSE:To offer a projection type displaying device in which the deterioration of the center part of a polarizing plate is restrained, furthermore, the brightness distribution of a projection screen is made uniform by decreasing the light quantity of the center part of the cross section of an incident luminous flux toward the polarizing plate. CONSTITUTION:This device contains the polarizing plate 7 having a light receiving surface to receive light projected from a light source 3 and a polarizing beam splitter 6; a light intensity distribution uniformizing filter 20 which is smaller than the cross section area of the incident luminous flux and which has a translucent area crossing with the optical axis of the incident luminous flux is arranged between the light source 3 and the polarizing plate 7.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a projection type display device having a projection optical system including a polarizing plate having a light receiving surface for receiving a light beam emitted from a light source and a polarizing beam splitter.

[0002]

BACKGROUND ART Such projection display devices include, for example, liquid crystal display devices using a photoconductive liquid crystal light valve or the like.
Such a photoconductive liquid crystal light valve includes a transmissive type in which a photoconductive layer is interposed between a liquid crystal layer and an electrode, and a reflective type in which a reflective layer or the like is further provided between the liquid crystal layer and the photoconductive layer. There is something.

FIG. 5 shows an example of the construction of such a reflection type projection type liquid crystal display device. In the figure, a photoconductive liquid crystal light valve 1 is coupled to the front face of a CRT 2. The CRT writes the image displayed on its front face to the photoconductive layer of each conductivity type liquid crystal light valve via 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, a light beam emitted from a light source 3 such as a metal halide lamp passes through a cold mirror 4, a condenser lens 5 and a polarizing plate 7 and enters a polarizing beam splitter 6. The P-polarized component of this incident light passes through the polarization beam splitter 6. The S-polarized component has its traveling direction bent by the polarization beam splitter 6 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 is in accordance with 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.

In such a high-luminance light source such as a metal halide lamp, since optical elements such as a polarization beam splitter and a polarizing plate are arranged in the housing of the projection type display device, the light passes through the polarizing plate and the polarizing beam splitter. Even if there is excess light that is not polarized (hereinafter referred to as leakage light), it reaches the downstream optical system, and eventually turns into heat. In addition, in order to increase the degree of polarization, it is common to provide a polarizing plate 7 upstream of the polarizing beam splitter 6 and attach the polarizing plate 7 to a polarizing beam splitter having a large heat capacity in order to prevent heat.

However, since the polarizing plate 7 absorbs about 60% of light, its polarization characteristics are deteriorated by heat. The polarization beam splitter has a high light absorption rate and a temperature performance limit. In addition, the light quantity distribution of the light flux from the metal halide lamp is high in the central portion, and the central portion of the light absorption type polarizing plate is deteriorated earlier than the surroundings due to heat. When the light flux is projected through the magnifying projection lens, the central portion becomes brighter.
Further, the light amount distribution of the light flux becomes the illuminance distribution of the actual projection screen, and it is difficult to obtain a uniform light amount distribution in the projected image of the screen. As described above, in the projection-type liquid crystal display device, the luminance unbalance of the projection and the decrease of the contrast are generated due to the light amount distribution of the light flux projected from the light source.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection type liquid crystal display device capable of enhancing the uniformity of brightness in the cross section of a parallel ray bundle for projection.

[0008]

A projection type display device of the present invention is a projection type display device including a polarizing plate having a light receiving surface for receiving light emitted from a light source and a polarization beam splitter, and having a size smaller than a cross-sectional area of an incident light beam. And a light intensity distribution uniformizing filter having a semitransparent region intersecting the optical axis of the incident light flux,
It is arranged between the light source and the polarizing plate.

[0009]

With this structure, it is possible to suppress the deterioration of the central portion of the polarizing plate by reducing the light amount of the incident light flux to the polarizing plate at the central portion of the cross section, and to make the brightness distribution of the projection screen uniform.

[0010]

FIG. 1 shows a projection type display device according to an embodiment of the present invention. The projection type display device includes a polarization beam splitter 6 for receiving light emitted from a light source, a light intensity distribution uniformizing filter 20 arranged between a polarizing plate 7 and the light source 3, and other components are shown in FIG. Are the same as those indicated by the same reference numerals. The light intensity distribution uniformizing filter 20 is attached to the incident surface of the polarization beam splitter 6 across the polarizing plate 7. This improves the heat dissipation effect.

As shown in FIG. 2, the light intensity distribution uniformizing filter 20 has a semi-transparent region 21 consisting of a frosted glass part formed of minute irregularities partially formed on a transparent glass flat plate 20a. The semitransparent region 21 is a semitransparent region that is smaller than the cross-sectional area of the incident light flux and intersects the optical axis of the incident light flux. Further, the semitransparent region 21 may be a reflective film which is partially formed on a transparent glass plate and is made of a metal used for a semitransparent mirror or the like. In this way, the central part of the glass substrate or the like is made into a frosted glass shape, or a filter having a thin aluminum film is prepared and installed in the optical system, whereby the amount of light in the central part can be suppressed. In principle, it may be installed at any position in the optical system, but for the purpose of cooling the polarizing plate 7, it is effective to use the structure shown in FIG. This is because the sandwich structure with glass has a uniform heat distribution and the polarizing plate is not deteriorated by heat.

The semi-transparent area 21 is shown in FIGS.
As shown in (a), for example, a frosted glass portion having the highest translucency, that is, not being opaque but having the lowest transmittance, or a reflection film having a high reflectance is circular in the vicinity of the optical axis of the incident light flux having a circular cross section It may be formed in. Depending on the cross-sectional shape of the incident light beam, it may be elliptical or the like. Furthermore, FIG.
As shown in (b), (c) and FIGS. 4 (b), (c), the semi-transparent region 21 has the highest semi-transparency in the passing portion in the vicinity of the optical axis of the incident light flux having a circular cross section, It is preferable to have a semi-transparency or reflectance distribution in which the transmittance gradually decreases with the radial direction away. The translucency or the reflectance in the translucent region 21 is hierarchical (FIG. 3B, FIG.
(B)) or by reducing the light quantity corresponding to the incident light flux end face (FIGS. 3C and 4C), the heat distribution to the polarizing plate can be made more uniform.

Furthermore, the semitransparent region may be directly provided on the polarizing plate 7 partially without providing it on the glass substrate or the like. That is, according to the present invention, in an optical system having a polarization beam splitter for polarizing light, a filter for homogenizing a light amount distribution obtained by performing a light amount reduction process on a central portion of a glass substrate is provided in front of the polarization beam splitter. I did.

[0014]

According to the present invention, the light amount distribution in the central portion of the cross section of the light flux incident on the polarizing plate is reduced to make the light amount distribution uniform, suppress the deterioration of the central portion of the polarizing plate, and increase the brightness of the projection screen. It is possible to obtain a projection type liquid crystal display device which makes the distribution uniform.

[Brief description of drawings]

FIG. 1 is a schematic view of a reflective projection type liquid crystal display device according to the present invention.

2 is a perspective view of a polarization beam splitter, a polarizing plate, and a light intensity distribution uniformizing filter of the projection type display apparatus of the embodiment shown in FIG.

FIG. 3 is a front view of a light intensity distribution uniformizing filter according to an embodiment.

FIG. 4 is a graph showing translucency corresponding to a radius from an optical axis in an opaque region of the light intensity distribution uniformizing filter shown in FIG.

FIG. 5 is a schematic view of a conventional reflection type projection type liquid crystal display device.

[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: Light intensity distribution uniformizing filter 21 ... Semi-transparent area

Claims (6)

[Claims] 1. A projection type display device including a polarizing plate having a light receiving surface for receiving light emitted from a light source and a polarization beam splitter, wherein an optical axis of the incident light flux is smaller than a cross-sectional area of the incident light flux. A projection type display device, characterized in that a light intensity distribution uniformizing filter having a translucent region intersecting with is disposed between the light source and the polarizing plate. 2. The semi-transparent region has a semi-transparency distribution in which the translucency of the passing portion near the optical axis of the incident light flux is highest and the translucency gradually decreases as the distance from the optical axis of the light flux increases. The projection type display device according to claim 1. 3. The uniform light intensity distribution filter has a transparent glass flat plate, and the semitransparent region is formed of a ground glass part made of fine irregularities partially formed on the transparent glass flat plate. The projection type display device according to claim 1 or 2. 4. The uniform light intensity distribution filter has a transparent glass plate, and the semitransparent region is formed of a reflective film partially formed on the transparent glass plate. 2. The projection display device according to 2. 5. The projection type projector according to claim 1, wherein the light intensity distribution uniformizing filter is attached to the incident surface of the polarization beam splitter with the polarizing plate interposed therebetween. Display device. 6. The semi-transparent region comprises a reflective film partially formed on the polarizing plate.
The projection display device described.