JPH03132746A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To make incident color light without color unevenness on each color modulating liquid crystal light valve and to display a high quality image without color unevenness on a screen by combining two types of dichroic mirrors whose wavelength selecting characteristics are changed according to an incident angle, and carrying out color separation. CONSTITUTION:In consideration of angled luminous flux emitted from a light source, and dichroic mirror dependency, two types of dichroic mirrors are used: their wave length characteristics are shifted on the optical paths A and B. Therefore, the wave length characteristic of reflected light and transmitted light on the sides of the optical paths A and B are equalized. The diffusion angle of the light emitted from the light source 1 varies with a lamp and a reflector, but since two types of dichroic mirrors are combined and used according to the light source 1, color unevenness can be prevented. Thus, color light without color unevenness can be made incident on each color modulating liquid crystal valve. Each direction of the color separated light is changed by a reflection mirror 6 and made incident on each of color modulating liquid crystal valves 7R, 7G, and 7B.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a projection type liquid crystal display device that uses a plurality of liquid crystal light valves for image formation and displays images by projecting the images.

[Prior Art] Conventionally, a projection type liquid crystal display device using a plurality of liquid crystal light valves uses a combination of two dichroic mirrors to separate the white light from the projection light source into three primary colors, and separates blue light and green light. was reflected at an incident angle of 45 degrees, and the remaining red light was transmitted to extract the three primary colors, which were then modulated, combined, and projected to display an image.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, the projection light source does not become an ideal point light source, and even if the light is focused, it tends to diffuse, and when the light enters the dichroic mirror, it cannot be accurately detected. Since it is not incident at 45 degrees,
Due to the angular dependence of dichroic mirrors, color unevenness occurs in both reflection and transmission depending on the incident angle. The problem is that the uneven colored light is modulated by a liquid crystal light valve and synthesized by a dichroic prism, and the uneven color is displayed as is on the screen.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide a projection type liquid crystal display device that displays high-quality images without color unevenness on a screen.

[Means for Solving the Problems] The projection type liquid crystal display device of the present invention includes three liquid crystal light valves for image formation, a dichroic mirror system for separating light into three primary colors, and a color image composition. A projection type liquid crystal display device comprising a dichroic prism, a light source, and a projection lens, characterized in that the dichroic mirror system is a combination of dichroic mirrors having different wavelength selection characteristics.

[Operation] By using a dichroic mirror that has different wavelength selection characteristics for the large incident angle part and the small incident angle part of light from a light source that tends to diffuse, the wavelength characteristics of reflected light and emitted light are made to be the same, thereby eliminating color unevenness. This makes it possible to allow color-free light to enter the liquid crystal light valve.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a projection type liquid crystal display device of the present invention.

White light emitted from a light source 1 such as a halogen lamp, a xenon lamp, or a metal halide lamp is collected by a parabolic reflector 2, enters a heat ray cut filter 3, becomes only visible light, and enters a dichroic mirror system. Here, a combination of an elliptical mirror or a spherical mirror and a condensing lens may be used as the condensing means. However, since the light source 1 is not a point light source, the light is not completely parallel, and the intensity of the light in the direction of diffusion is high.

In this way, the focused light enters a dichroic mirror system for color separation. The dichroic mirror system for color separation is
It is composed of a blue reflective dichroic mirror 4, a green reflective dichroic mirror 5, and a reflective mirror 6. The blue reflective dichroic mirror 4 consists of two types, a blue reflective dichroic mirror 4A and a blue reflective dichroic mirror 4B, and the green reflective dichroic mirror 5 consists of two types, a green reflective dichroic mirror 5A and a green reflective dichroic mirror 5B.

FIG. 2(a) is a wavelength characteristic diagram of the blue reflective dichroic mirror 4, where the solid lines indicate the blue reflective dichroic mirror 4A,
The dotted line is the characteristic of S-polarized light of the blue reflective dichroic mirror 4B. FIG. 2(b) is a wavelength characteristic diagram of the green reflective dichroic mirror 5, where the solid line is the characteristic of the P polarized light of the green reflective dichroic mirror 5A, and the dotted line is the characteristic of the P polarized light of the green reflective dichroic mirror 5B. In each case, the horizontal axis represents the wavelength, and the vertical axis represents the transmittance, and the incident angle is 45 degrees. Hereinafter, when the wavelength is expressed numerically, it is assumed that the transmittance is 50%.

In this color separation, as mentioned above, the light from light source 1 is not parallel light but has a tendency to diffuse, so between optical path A and optical path B in the optical path diagram of Fig. As a result, the angle of incidence on optical path B becomes larger than 45 degrees.

Figure 3(a) is a characteristic diagram showing the angle dependence of a general blue reflective dichroic mirror (500 [nm1).
Figure (b) shows a general green reflective dichroic mirror (5
90 [nIfi]). FIG.

As can be seen from this figure, when the incident angle changes, the wavelength selection characteristics change. When the angle of incidence increases, the reflected light shifts to the short wavelength side, and when the angle of incidence decreases, it shifts to the long wavelength side. The transmitted light corresponds to the reflected light and is shifted respectively.

In other words, regarding green light, yellowish green light is incident on the green modulation liquid crystal light valve 7G on the optical path A side, and bluish greenish light is incident on the optical path B side.

In the present invention, the light flux emitted from the light source 1 at an angle and the angle dependence of the dichroic mirror are taken into consideration.
Two types of dichroic mirrors with shifted wavelength characteristics are used on the optical path A side and the optical path B side. (See FIGS. 2(a) and 2(b)) Therefore, the wavelength characteristics of the reflected light and the transmitted light on the optical path A side and the optical path B side are approximately equal.

In this example, when the diffusion angle is ±5 degrees, the blue reflective dichroic mirror 4A has a density of 505 [nml, the blue reflective dichroic mirror 4B has a density of 495 [nml], and the green reflective dichroic mirror 5A has a density of 588 [nml].
l, green reflective dichroic mirror 5B is 569 [n
ml combination, the color unevenness on the screen was minimized. Furthermore, the chromaticity of the three primary colors displayed on the screen is determined by approximately the average value of the wavelength characteristics of the two types of dichroic mirrors combined. Blue light is approximately 500 [nml or less wavelength region, green light is approximately 510 [no+J to 58]
0 [n@J wavelength range, red light is approximately 590 [nm
1 or more wavelength regions. Note that the diffusion angle of the light emitted from light source 1 differs depending on the lamp handle, and by using a combination of two types of dichroic mirrors corresponding to light source 1 from one device to another, it is possible to eliminate color unevenness. It is.

In this way, color light without color unevenness is incident on the modulation liquid crystal light valve of each color. The separated color lights each change their direction by a reflecting mirror 6, and are sent to a liquid crystal light valve 7R for modulating each color.

Injects into 7G and 7B.

The liquid crystal light pulps 7R, 7G, and 7B for modulating each color use an active matrix liquid crystal panel, apply a signal voltage for each color, and control the transmittance for each color depending on the magnitude of the voltage to form an image. Here LCD Light Pulp 7R
, 7G, and 7B perform the function of a shutter that controls the transmittance of incident light, so they can be used not only as an active matrix liquid crystal panel or a time-division drive liquid crystal panel, but also as long as they are liquid crystal panels whose transmittance is varied by a signal voltage. . Furthermore, it is also possible to replace it with a valve whose transmittance can be controlled mechanically, electromagnetically, or the like.

Since the liquid crystal light pulps 7R, 7G, and 7B are in a normally black mode (transmits when a voltage is applied), polarizing elements (not shown) with the same polarization axis are used on the light input and output sides. ing. The blue modulation liquid crystal light valve 7B and the red modulation liquid crystal light valve 7R correspond to S-polarized light (direction parallel to the drawing), and the green modulation liquid crystal light valve 7G corresponds to P-polarization (direction perpendicular to the drawing). . This is to minimize the attenuation of colored light and display a bright image without overlapping the wavelength separation characteristics of the guichroic mirror system for color separation and the 80 wavelength synthesis characteristics of the guichroic prism for color synthesis.

The colored lights modulated by the liquid crystal light pulps 7R, 7G, and 7B enter the dichroic prism 8, are combined, and are enlarged and projected onto a screen by the projection lens 11 to display a color image.

The dichroic prism 8 is configured such that the red reflective surface 9 and the blue reflective surface 10 are orthogonal to each other. This is a rectangular prism with dielectric multilayer films deposited on both sides of the right angle, and four films are pasted together around the right angle.

The spectral characteristics of the red reflective surface 9 are such that it transmits the blue wavelength region of the S-polarized light component, reflects the red wavelength region, and transmits the blue-green wavelength region of the P-polarized light component (the solid line in FIG. S
The dashed line is the P polarization characteristic). Blue reflective surface 1
The spectral characteristics of 0 transmit the red wavelength region of the S-polarized light component, reflect the blue wavelength region, and transmit the yellow wavelength region of the P-polarized light component (the dashed line in Figure 4 indicates the S-polarized light characteristic The two-dot chain line is the P polarization characteristic).

The projection lens 11 can display a bright image by using a lens with a small F value.

Even if the order of color separation is changed, the mode of the liquid crystal panel is changed, or the polarization characteristics are S-polarized or P-polarized, the present invention enables image display without color unevenness. Needless to say. Furthermore, the present invention is also effective in color synthesis systems using dichroic mirrors in addition to dichroic prisms.

[Effects of the Invention] As described above, according to the present invention, by performing color separation by combining two types of dichroic mirrors with different wavelength selection characteristics depending on the incident angle, color light without color unevenness can be modulated for each color. This allows the light to enter the liquid crystal light valve, which has the effect of allowing high-quality image display without color unevenness on the screen.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of a projection type liquid crystal display device of the present invention. FIG. 2(a) is a wavelength characteristic diagram of a blue reflective dichroic mirror, and FIG. 2(b) is a wavelength characteristic diagram of a green reflective dichroic mirror. FIG. 3(a) is a characteristic diagram showing the angular dependence of the blue reflecting dichroic mirror, and FIG. 3(b) is a characteristic diagram showing the angular dependence of the green reflecting dichroic mirror. FIG. 4 is a wavelength characteristic diagram of the red reflecting surface and the blue reflecting surface of the dichroic prism. 1... Light source 4... Blue reflective dichroic mirror 4A... Blue reflective dichroic mirror A 1st FIII 4 B ・ 5 ・ A B R G B 8 ・ 11 ・ Blue reflective dichroic mirror B Green reflective dichroic mirror Green reflective dichroic mirror A Green reflective dichroic mirror B Red modulation liquid crystal light valve Green modulation liquid crystal light valve Blue modulation liquid crystal light valve Dichroic prism projection lens or higher

Claims (1)

[Claims] In a projection type liquid crystal display device consisting of three liquid crystal light valves for image formation, a dichroic mirror system for separating light into three primary colors, a dichroic prism for color image synthesis, a light source and a projection lens, A projection type liquid crystal display device, wherein the dichroic mirror system is a combination of dichroic mirrors having different wavelength selection characteristics.