JPH04142530A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To display an image of high picture quality which has no irregularity on a screen by using a dichroic prism which varies continuously in wavelength selectivity with an angle of incidence for a means for color image composition. CONSTITUTION:The white light emitted by a light source 1 is passed through a parabolic reflector 2 and a cut filter 3 to extract only nearly parallel visible light, which is made incident on the dichroic mirror system and separated into red light, green light, and blue light. The respective color-separated color lights are made incident on liquid crystal light valves 7R, 7G, and 7B for color modulation; and condenser lenses are arranged on the incidence sides of the respective valves to improve the brightness and reduce the illuminance irregularity. The respective modulated color lights are made incident on the dichroic mirror and multiplexed, and projected on the screen to display a color image. This prism has its astigmatism removed and dielectric multi-layered film coats are varied and equalized in wavelength selectively according to the inclination of the main light beam of a projection lens to generate no color shade. Further, the optical path length is made short corresponding to the refractive index, so the back focus of the projection lens is shortened and the projection image of high quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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 two color separation dichroic mirrors 22 to separate white light from a projection light source 21, as shown in FIG. Using a combination of mirrors 23 and 23, green light and red light are reflected at an incident angle of 45 degrees, and the remaining blue light is transmitted to extract the three primary colors.Each color light is modulated by a liquid crystal light valve 24, and 2 is used as color image synthesis means. Three colors are synthesized using a combination of a dichroic mirror 25 for color synthesis and a mirror 23, and the image is displayed by enlarging and projecting the image using a projection lens 26.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, when a liquid crystal light valve becomes high-definition, when trying to use a projection lens whose principal ray is parallel without astigmatism, other projection lens It is not suitable for practical use because its performance deteriorates, its size becomes large, and its price becomes extremely high.

Therefore, if a projection lens with a tilted principal ray is used, the dichroic mirror of the color image synthesis means included in the projection lens system becomes an optical system that is non-rotationally symmetrical with respect to the optical axis of the projection lens, causing astigmatism and reducing resolution. , resulting in deterioration of image quality such as a decrease in contrast ratio. Furthermore, if a projection lens with an inclined principal ray is used, the angle of incidence on the dichroic mirror varies depending on the location and the wavelength selection characteristics vary, resulting in problems such as color unevenness.

The present invention is intended to solve these problems, and its purpose is to display a high-resolution, high-quality image without color unevenness on a screen, and to provide a projection system that is compact, lightweight, and inexpensive. type liquid crystal display device.

[Means for Solving the Problems] A projection type liquid crystal display device of the present invention includes a liquid crystal light valve for image formation, a dichroic mirror system for color separation of light, means for color image synthesis, and a light source. and a projection type liquid crystal display device comprising a projection lens, characterized in that the means for color image synthesis uses a dichroic prism whose wavelength selection characteristics are continuously changed.

[Function] In the projection type liquid crystal display device having the above configuration, the modulated light from each liquid crystal light valve corresponding to each primary color is
The images are combined by a color image combining means consisting of a combination of a plurality of dichroic prisms and reflective prisms, and are enlarged and projected onto a screen in front of the projection lens. At this time, even if the principal ray of the projection lens is tilted, the dichroic prism forms an optical system that is rotationally symmetrical with respect to the optical axis, thereby eliminating astigmatism. Furthermore, by changing the wavelength selection characteristics of the dielectric multilayer coating of the dichroic prism according to the inclination of the principal ray of the projection lens, the wavelength selection characteristics are made equal and color unevenness does not occur. In addition, in an optical system using a dichroic mirror, most of the space that used to be air with a refractive index of about 1.0 can be replaced by air with a refractive index of about 1.0.
By filling the lens with glass having a refractive index of 5, the optical path length can be shortened by a value corresponding to the refractive index of the glass, thereby shortening the back focus of the projection lens. Therefore, the projected image will be of high quality, and the projector can be made smaller, lighter, and less expensive.

[Example code] 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, xenon lamp, metal halide lamp, etc. is collected by a parabolic reflector 2, enters an infrared and ultraviolet cut filter 3, and only approximately parallel visible light is extracted. . Here, a combination of an elliptical mirror or a spherical mirror and a condensing lens may be used as the condensing means.

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-green reflective dichroic mirror 4, a green reflective dichroic mirror 5, and a reflective mirror 6.

First, among the white light incident on the blue-green reflective dichroic mirror 4, red light (approximately 600±20 [nm1 or more wavelength range) is transmitted, and blue-green light (approximately 600±20 [nm1 or more wavelength range)] is transmitted.
m] wavelength range below) is reflected. The transmitted red light is redirected by a reflective mirror.

The reflected blue-green light enters the green reflecting dichroic mirror 5, and the green light (approximately 500±20 to 600±20
[r+m] wavelength range) is reflected, and blue light (approximately 500
±20 (wavelength range of nml or less) is transmitted. In FIG. 2, the wavelength characteristics of the blue-green reflective dichroic mirror 4 are shown by a solid line, and the wavelength characteristics of the green-reflecting dichroic mirror 5 are shown by a dotted line. Note that the characteristics of the red region of the green reflecting dichroic mirror 5 can be freely determined. The polarized light component is a characteristic of the P polarized light component, as will be described later. The wavelength is plotted on the horizontal axis and the transmittance is plotted on the vertical axis, and the incident angle is 45 degrees. Hereinafter, when the wavelength is expressed numerically, it is assumed that the transmittance is 50%. In this embodiment, since a metal halide lamp was used as the light source 1, the blue-green reflective dichroic mirror 4 was set at 59 mm according to its light emission characteristics.
3 [nm], green reflective dichroic mirror 5 is 50
7 [nm].

The color-separated light beams enter respective color modulation liquid crystal light valves 7R, 7G, and 7B. Since each color light is almost parallel light, the condenser lens (not shown) is connected to the liquid crystal light valve 7R according to the inclination of the principal ray of the projection lens.
, 7G, and 7B light incident side to improve brightness and reduce uneven illuminance.

The liquid crystal light valves 7R, 7G, and 7B for each color modulation use active matrix liquid crystal panels, apply signal voltages for each color layer, and control transmittance for each color depending on the voltage magnitude to form an image. Here, LCD light bulb 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 valves 7R, 7G, and 7B are TN type in normally white mode (transmittance decreases when a voltage is applied), polarizing elements (not shown) whose polarization axes are orthogonal are used on the light input and output sides. ) is used. The polarizing element is P-polarized light (horizontal to the drawing) in a dichroic mirror system.
The image synthesis and projection optical system supports S-polarized light (direction perpendicular to the drawing). This is achieved by using a medium with a high refractive index relative to the vapor deposition surface (with a refractive index of approximately 1
．． 5) This is because when more light is incident, the wavelength separation characteristics are better for the S polarization component as shown in Figure 3, and with a mirror, almost the same characteristics can be obtained regardless of which polarization component. It's for a reason. With this configuration, a bright image with good color reproducibility is displayed. Furthermore, since the polarizing element generates heat when using a polarizing plate that absorbs light, it is installed at a distance so as not to affect the liquid crystal light valve, and is forcedly cooled by an air cooling fan.

In addition, the pre-polarizer is connected to light source 1 and liquid crystal light valve 7R,
Heat countermeasures can be taken by inserting it between 7G and 7B and removing unnecessary polarized light components, or by using a polarizing element that does not absorb.

The light of each color modulated by the liquid crystal light valves 7R, 7G, and 7B enters a dichroic prism, which is a means for color image synthesis, is synthesized, and is enlarged and projected onto a screen by a projection lens 11 to display a color image. .

A dichroic prism serving as a means for color image synthesis is composed of a green reflective dichroic prism 8, a blue reflective prism 9, and a reflective prism 10.

The red light modulated by the red modulation liquid crystal light valve 7R passes through the green reflective dichroic prism 8, further passes through the blue reflective dichroic prism 9, and reaches the projection lens 11. Further, the green light modulated by the green modulation liquid crystal light valve 7G is reflected by the green reflective dichroic prism 8, transmitted through the blue reflective dichroic prism 9, and reaches the projection lens 11. Further, the blue light modulated by the blue modulation liquid crystal light valve 7B is reflected by the reflection prism 10, further reflected by the blue reflection dichroic prism 9, and reaches the projection lens 11.

FIG. 4(a) is a wavelength characteristic diagram of the green reflective dichroic prism 8, in which the solid line is the characteristic of the central portion, the dotted line is the characteristic of the optical path A portion, and the dashed line is the characteristic of S-polarized light in the optical path 8 portion.

FIG. 4(b) is a wavelength characteristic diagram of the blue reflecting dichroic prism 9, in which the solid line is the characteristic of the central portion, the dotted line is the characteristic of the optical path A portion, and the dashed line is the characteristic of S polarized light in the optical path 8 portion.

In each case, the horizontal axis represents the wavelength, and the vertical axis represents the transmittance, and the incident angle is 45 degrees.

In this color image synthesis, since the principal ray of the projection lens 11 is not parallel but has an inclination, the optical path A of the principal ray in FIG.
At section A and section 8 of optical path, the angle of incidence at section A of optical path is smaller than 45 degrees, and the angle of incidence at section 8 of optical path is larger than 45 degrees.

Figure 5 (a) is a characteristic diagram showing the angle dependence of a green reflective dichroic prism (590 [nm1) for boat fishing, and Figure 5 (b) is a characteristic diagram showing the angle dependence of a blue reflective dichroic prism (500 [n1l) for boat fishing]. FIG. 2 is a characteristic diagram showing the angle dependence of .

Each is a characteristic of the S polarization component. As can be seen from this figure, when the incident angle changes, the wavelength selection characteristics change. The reflected light shifts toward shorter wavelengths as the angle of incidence increases, and shifts toward longer wavelengths as the angle of incidence decreases. The transmitted light corresponds to the reflected light and is shifted respectively. In other words, regarding green light, yellowish green light is imaged on the screen on the optical path A side, and bluish greenish light is imaged on the optical path B side.

In the present invention, the inclination of the principal ray of the projection lens 11,
Considering the angular dependence of the dichroic prism, the optical path A
A dichroic prism whose wavelength selection characteristics are continuously changed from the first part to the third part of the optical path is used. (Figure 4(a)
and FIG. 4(b)) Therefore, the optical path A part and the optical path 3
The wavelength characteristics of the reflected light and the transmitted light at the part are almost equal.

In this example, when the principal ray maximum inclination angle is ±8 degrees,
The wavelength selection characteristics of the green reflective dichroic prism 8 are 593 (r+II!) at the center and 578 [r+II!] at the optical path A section.
nml, 608 [nm] in the 3rd part of the optical path, 507 [rvl] in the center of the blue reflective dichroic prism 9, 495 [nm] in the A part of the optical path,
By using a dichroic prism that was continuously controlled to have an optical wavelength of 519 [nm] in three parts of the optical path, color unevenness on the screen was minimized. In other words, reflection and transmission are performed with the same wavelength characteristics as at the center, whether at the incident angle at the optical path section A or at the incident angle at the optical path section 3.

Furthermore, the chromaticity of the three primary colors displayed on the screen is approximately determined by the wavelength characteristics of the color separation dichroic mirror system and the center of the dichroic prism.

Blue light has a wavelength range of approximately 507 [nm] or less, green light has a wavelength range of approximately 507 [nm] to 593 [nm], and red light has a wavelength range of approximately 593 [nm] or more.

If you want to further increase the color purity of green and achieve the desired white balance, insert a green filter (for example, transmits the wavelength range from 510 to 560 [nm]) on the light incident side of the green modulation liquid crystal light valve 7G. This becomes possible.

The maximum inclination angle of the principal ray of the projection lens 11 varies depending on the design concept such as lens performance, size, price, etc., and varies from a few degrees to several degrees, and the wavelength selection characteristics of the dichroic prism ( If the wavelength characteristics (wavelength characteristics from optical path section A to optical path section 3) are optimally selected, it is possible to eliminate color unevenness with any projection lens 11.

Such wavelength selection characteristics can be achieved by partially changing the distance from the evaporation source, that is, by setting the evaporator so that the evaporation surface is oblique to the evaporation source. It is created by vapor deposition in the same way as the coat. At this time, as the distance from the deposition source changes, the film thickness changes and the wavelength selection characteristics change, and furthermore, by continuously controlling the film thickness within the evaporation surface, the wavelength selection characteristics also change continuously. A dichroic prism is formed by forming this film on the slope of a right-angle prism and bonding it to the slope of another right-angle prism to form a cube.

The reflective prism 10 equalizes the optical path length from the three-color liquid crystal light valve with a blue-red edge to the projection lens 11, and the reflective surface uses a combination of total internal reflection and an A1 reflective coating or a dielectric multilayer coating to increase the reflectance. It's increasing. Furthermore, the light entrance and exit surfaces of these prisms are coated with anti-reflection coatings to increase brightness.

The projection lens 11 can display a bright image by using a lens with a small F value. Furthermore, since the principal ray can be tilted, and a dichroic prism with a refractive index of about 1.5 is included in the optical path, the back focus can be shortened, making it possible to reduce the size, weight, and cost. Astigmatism hardly occurs because it is rotationally symmetrical about the optical axis.

FIG. 7 is a plan view showing another embodiment of the present invention, showing only the color image synthesis portion. The three primary colors of red, green, and blue light enter the respective color modulation liquid crystal light valves 7R, 7G, and 7B, are modulated, and then enter the dichroic prism 31, which is a means for color image synthesis. This dichroic prism 31 is made by pasting together four right-angled prisms, and has a configuration in which a red reflective surface 32 and a blue reflective surface 33 intersect in a cross shape. Similar to the embodiment described above, the wavelength selection characteristics in the optical path A section and the optical path 3 section are changed with respect to the central part.

The angle of incidence is small in the part where the optical path A is incident on the red reflective surface 32, and the angle of incidence is large in the part where the optical path B is incident on the red reflective surface 32, so the red reflective surface 32 is on the short wavelength side in the part of the optical path A. The wavelength selection characteristics from the optical path A part to the optical path 8 part are continuously changed so that the wavelength is shifted to the long wavelength side in the optical path part 8 part. In addition, the angle of incidence is large in the portion where the optical path A is incident on the blue reflective surface 33, and the angle of incidence is small in the portion where the optical path B is incident on the blue reflective surface 33.
The blue reflecting surface 33 continuously changes the wavelength selection characteristic from the optical path A part to the optical path 8 part so that it shifts to the long wavelength side in the optical path A part and shifts to the short wavelength side in the optical path 8 part.

In this way, the selection characteristics are the same from part A to part B of the optical path,
Image display without color unevenness is performed through the projection lens 11.

The present invention is effective for all projection type liquid crystal display devices that separate white light into a plurality of colors, modulate each color, combine them, and project them. It goes without saying that even if the mode of the liquid crystal panel changes (including reflective type), the present invention allows image display without color unevenness.

[Effects of the Invention] As described above, according to the present invention, since a dichroic prism whose wavelength selection characteristics are continuously changed according to the incident angle is used as a means for color image synthesis, color unevenness on the screen can be reduced. It is possible to display high-quality images that are not available before.

In addition, it is possible to eliminate astigmatism in the projection lens and display high-definition images, and because the principal ray can be tilted and the back focus can be shortened, the projection lens and main body can be made smaller, lighter, and less expensive.

These effects are particularly great when displaying high-definition or even higher-definition images because the size of the liquid crystal light valve increases and the density increases.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of a projection type liquid crystal display device of the present invention. (The optical path A and the optical path B are also shown at the same time.) FIG. 2 is a wavelength characteristic diagram of a blue-green reflective dichroic mirror and a green reflective dichroic mirror. FIG. 3 is a wavelength characteristic diagram showing the polarization characteristics of a dichroic prism. FIG. 4(a) is a wavelength characteristic diagram of a green reflective dichroic prism, and FIG. 4(b) is a wavelength characteristic diagram of a blue reflective dichroic prism. FIG. 5(a) is a characteristic diagram showing the angular dependence of the green reflecting dichroic prism, and FIG. 5(b) is a characteristic diagram showing the angular dependence of the blue reflecting dichroic prism. FIG. 6 is a plan view of a conventional projection type liquid crystal display device. FIG. 7 is a plan view showing another embodiment of the projection type display device of the present invention. 1 ・ 2 ・ 3 ・ 4 ・ 5 ・ 6 ・ RGB 8 ・ 9 ・ Light source, parabolic reflector, infrared and ultraviolet cut filter, blue-green reflective dichroic mirror, green reflective dichroic mirror, reflective mirror, red modulation liquid crystal Light valve, green modulation liquid crystal light valve, blue modulation liquid crystal light valve, green reflective dichroic prism, blue reflective dichroic prism, reflective prism, projection lens, dichroic prism, red reflective surface, blue reflective surface or higher

Claims (1)

[Claims] In a projection type liquid crystal display device comprising a liquid crystal light valve for image formation, a dichroic mirror system for color separation of light, a means for color image synthesis, a light source, and a projection lens, A projection type liquid crystal display device characterized in that the means uses a dichroic prism whose wavelength selection characteristics are continuously changed.