JPH0458242A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a device in which a projected image is bright and display quality is excellent by using a composite prism in which the separation and the composition of three primary colors are performed by two dichroic surfaces having small incident angle of luminous flux and having no intersection part. CONSTITUTION:The luminous flux emitted from a light source device passes through a polarizing plate 104 and is condensed on a minute mirror 105 arranged to be a little deviated from the focusing position of a projection lens 106, reflected at the angle of about 45 deg., turned into nearly collimated beam of light by the lens 106 and then passes through the composite prism 107 to be spectrally splitted to three primary colors. The luminous fluxes spatially and temporally modulated by active matrix system reflection type liquid crystal panels 108, 109 and 110 corresponding to the light of the respective colors are made incident on the prism 107 again and composited to be the color light. The luminous flux including color image information passes the lens 106 and is temporarily condensed near the minute mirror and analyzed by a polarizing plate 111, then formed into an image on a screen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection type liquid crystal display device that displays video images and the like on a screen.

[Prior Art] Projection type liquid crystal display devices generally convert image information electrically written into an active matrix type liquid crystal light valve into an optical image and enlarge and project it on a screen, making it compact and high definition. A device using reflective liquid crystal pulp that makes this possible is being developed. An example of the configuration of a projection type liquid crystal display device using a conventional reflective type liquid crystal light pulp is shown in Figure 2, in which a dichroic prism 201 is used to separate the three primary colors of white light and combine the liquid crystal panel modulated light. . Since the optical system is a non-optical projection system, the angle of incidence with respect to the dichroic color light separation surface is different between the light flux that enters the dichroic prism from the projection lens side and the light flux that enters the dichroic prism from the reflective liquid crystal panel. Further, the light beam is almost parallel light in order to prevent the polarization direction from changing due to the influence of the dichroic surface.

[Problem to be Solved by the Invention] However, in the above-mentioned conventional technology, since the light beam incident on the dichroic prism is almost parallel light, the shadow of the deficient part of the dichroic film on the line segment where the dichroic color light separation plane intersects is reflected in the projected image. The angle of incidence on the dichroic surface is different for the light beam heading toward the liquid crystal panel and the light beam reflected from the liquid crystal panel, so the spectral characteristics change due to the angle dependence of the spectral characteristics of the dichroic film. The amount of light will be lost accordingly.

In addition, the spectral characteristics of a dichroic surface with a 45-degree incidence generally vary greatly depending on the polarization direction of the incident light, and when the polarization direction entering the liquid crystal panel and the polarization direction extracted from the reflected light are orthogonal, the characteristics for each polarization direction will differ. The amount of light will be lost by the difference. In addition, two of the light beams containing image information reflected from the reflective liquid crystal panels corresponding to the three primary colors are mirror-inverted and one is not, so at least two types of panels are required. It has many problems. The present invention is intended to solve these problems, and its purpose is to provide a projection type display device that has excellent display quality, reduces light loss, and can be used with only one type of liquid crystal panel. be.

[Means for Solving the Problems] In the projection type liquid crystal display device of the present invention, the color light separation/synthesizer is a composite prism having at least two dichroic color light separation surfaces, and the white light incident on the composite prism is first color separated. The angle of incidence on the dichroic surface is 2
1 to 31 degrees, and the angle at which the light flux transmitted through the dichroic surface is incident on the dichroic surface where the next color is separated is 10 to 17 degrees, and the light flux reflected by each dichroic surface is between the glass material and the air. The light beam is reflected again by the optically flat surface that is the interface between the two dichroic surfaces, and then is emitted, and the light beam that has passed through the two dichroic surfaces is emitted without being reflected even once.

[Function] According to the above configuration of the present invention, since the angle of incidence of the light beam on the dichroic surface is relatively small, the difference in spectral characteristics between S-polarized light and p-polarized light is small, and the spectral characteristics change with respect to changes in the angle of incidence. Since the change is small, the loss of light amount is extremely small. Furthermore, since there is no intersection of dichroic surfaces, the incident light beam is spatially uniformly dispersed. Also, since the light beams of each of the three primary colors passing through the compound prism are either reflected twice or never reflected within the compound prism,
The reflective liquid crystal panels used may all be of the same type.

[Example] (Example 1) FIG. 1 is a structural plan view showing a first example of a projection type liquid crystal display device according to the present invention. spherical reflector 101,
A light beam emitted from a light source device composed of a white light source lamp 102 and a condensing lens 103 passes through a polarizing plate 104 and is condensed onto a micromirror 105 placed slightly away from the focal point of the projection lens 106. It is reflected at an angle of approximately 45 degrees. The reflected light beam is turned into substantially parallel light by the projection lens 106, passes through a compound prism 107, and is separated into three primary colors. Active matrix reflective liquid crystal panels 108, 109, 1 corresponding to each color light
The light beam spatially and temporally modulated by the light beam 10 enters the composite prism 107 again and undergoes color light synthesis. The light beam containing this color image information passes through the projection lens 106 and is once condensed in the vicinity of the micromirror.
The light is analyzed and imaged on a screen. Note that the transmission axis of the polarizing plate 104 is such that the incident light on the micromirror 105 is S-
Since the light is adjusted so that it enters as polarized light, the direction of polarization will not be changed by the micromirror 105. In addition, since the polarizing plate 111 is arranged in a crossed nicol relationship with the transmission axis of the polarizing plate 104, the projection lens 106, the compound prism 107, the surfaces of the reflective liquid crystal panels 108, 109, 110, etc. Since the reflected unmodulated light is absorbed by the polarizing plate 111 and only the modulated light from the reflective liquid crystal panels 108, 109, 110 is extracted, a relatively high contrast ratio can be easily obtained.

FIG. 3 is a plan view showing an example of the configuration of a composite prism. Blue light reflective dielectric multilayer! It is composed of a triangular prism 31 on which 34 is deposited, a triangular prism 32 on which a red light reflective dielectric multilayer film 35 is deposited, and a square prism 33. The triangular prism 32 and the quadrangular prism 33 are in contact with each other, and are adhered with optical glue. When the white light 36 is incident on this composite prism, it first enters the blue light reflective dielectric multilayer M34 at around 25.7 degrees and only the blue light is reflected, and the reflected blue light is totally reflected by the optical plane of the triangular prism. After that, it is emitted.

The transmitted light flux enters the triangular prism 32, and then enters the red light reflective dielectric multilayer film 35 at an angle of about 12.9 degrees, and only the red light is reflected. The reflected red light is totally reflected by the optical plane of the triangular prism and then exits. The transmitted light flux, ie, the green light, passes through the square prism 33 and exits. Note that the optical path lengths for each of the three primary color lights are all equal.

Figure 4 shows the blue reflective dielectric multilayer film 34 inside the composite prism.
This is a characteristic diagram showing an example of the spectral reflection characteristics of the glass material, and the refractive index of the glass material is 1.52, and the refractive index of each of the high dielectric constant film and low dielectric constant film in the dielectric multilayer film is 2.2.1. This is the characteristic for case 7. The characteristics 41 for p-polarized light and the characteristics 42 for S-polarized light are slightly different, but the incident angle is 25.
Since it is relatively small at around 7 degrees, for example, when the incidence is 45 degrees, the difference in characteristics between p-polarized light and S-polarized light is at least about 30 ni+
It's pretty small compared to what it is. Also, although not shown in the figure, the change in characteristics with respect to changes in the incident angle is also smaller than in the case of 45-degree incidence, for example, and this is due to the fact that the refractive index of the dielectric film is n, the film thickness is t, and the interface of II When the traveling angle of the light is θ, the optical path difference of the light reflected by the dielectric film can be expressed as 2nt-cosθ, and it can be seen that the smaller θ is, the smaller the amount of change in the optical path length with respect to the change in θ. It is clear that there is little change in .

Figure 5 shows the red light reflective dielectric multilayer film 3 inside the composite prism.
5 is a characteristic diagram showing an example of the spectral reflection characteristics of No. 5, and the refractive index of each of the glass material, high dielectric constant film, and low dielectric constant film is the same as that of the blue light reflective dielectric multilayer film. The angle of incidence is 12.
Since it is even smaller at around 9 degrees, the characteristic for p-polarized light 5
The difference between the characteristics 52 for 1 and S-polarized light is extremely small, and the change in spectral characteristics due to the amount of change in the incident angle is also very small.

(Embodiment 2) FIG. 6 is a structural plan view showing a second embodiment of a projection type liquid crystal display device according to the present invention. A substantially parallel light beam emitted from a light source device constituted by a parabolic rotating surface reflector 601 and a light source lamp 602 is reflected by a mirror 603 and then becomes polarized light by a polarizing plate 604 and enters a composite prism 605 . The light beams separated into three primary colors by the dichroic surface are modulated by reflective liquid crystal panels 606, 607, and 608, and then combined by a composite prism. Thereafter, the light beam analyzed by the polarizing plate 609 passes through the projection lens 610 and forms an image on the screen. Note that the transmission axis of the polarizing plate 604 is aligned so that the transmitted polarized light is incident on the dichroic surface as S-polarized light or p-polarized light, so the direction of polarization hardly changes. Furthermore, since the polarizing plate 609 is arranged in a crossed nicol relationship with respect to the polarizing plate 604, only the light beam modulated by the liquid crystal panel is transmitted, making it easy to obtain a high contrast ratio.

(Embodiment 3) FIG. 7 is a structural perspective view showing a third embodiment of the projection display device of the present invention. Elliptical rotating surface reflector 70
2 and a light source lamp 701 is reflected by a mirror 703, and then
The light enters a composite prism 704 and is separated into three primary color lights. And each color light is reflected by a reflective liquid crystal light valve 705,
The light is modulated by 706 and 707, that is, the amount of spatially reflected light changes depending on the image information, and is taken out.The light enters the composite prism again, where color light synthesis is performed, and the light is emitted. After that, the light beam that almost converges on the projection lens 708 and passes through it forms an image on the screen surface, and the liquid crystal light valve 705,
Color images electrically input to 706 and 707 are displayed.

FIG. 8 is a sectional view showing the structure of the liquid crystal light valve used in this embodiment and its vicinity. The liquid crystal light valve mainly uses polarizing plate 803 and 1/4 wavelength plate 805.
, a reflective liquid crystal panel 806, and the angle between the transmission axis of the polarizing plate 803 and the main cross section of the 174-wavelength plate 805 is approximately 45 degrees. Unpolarized light 807 exiting through glass material 801 first becomes polarized light by polarizing plate 803, and then becomes circularly polarized light by quarter-wave plate 805.

The reflective liquid crystal panel 806 is a panel that uses an active matrix method to electrically control the retardation of liquid crystal in each pixel, and therefore can electrically control the polarization state of incident polarized light. If the circularly polarized light is not modulated, the circularly polarized light incident on the reflective liquid crystal panel 806 is reflected by the reflective electrode, becomes reversely circularly polarized light, enters the quarter-wave plate 805, and then becomes linearly polarized light. All of the light is absorbed by the polarizing plate 803.

Further, when the light is modulated, the light is transmitted through the polarizing plate 803 depending on the degree of modulation. In other words, since this reflective liquid crystal light valve is a light valve that extracts modulated light, the reflected light from the advance film, the interface of each layer, and the glass surface in the reflective liquid crystal panel 806 and 1/4
The light reflected from the surface of the wavelength plate 805 on the reflective liquid crystal panel 806 side can be absorbed by the polarizing plate 803, and a high contrast ratio can be easily obtained. Note that the quarter-wave plate 805, polarizing plate 803, and glass material 801 are bonded to each other with optical glue 802 and 804, and their respective refractive indexes are approximately equal, so there is almost no reflection from the bonded surfaces, and there is no loss of light quantity or decrease in contrast ratio. Does not occur.

In this embodiment, since it is a tilting optical system, it is suitable for a front projection type display device.

[Effects of the Invention] As described above, according to the present invention, a color light separation/synthesizer in a projection type liquid crystal display device using a reflection type liquid crystal light valve can be used by using two dichroic surfaces with a small incident angle of light flux and no intersection. Since a composite prism that separates and combines the three primary colors is used, the light utilization efficiency is high, resulting in a bright projected image and good display quality. Furthermore, since each of the three primary colors is reflected twice by the optical surface within the composite prism, or is not reflected at all, the same type of panel can be used as the liquid crystal panel, which is advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 1 is a plan configuration diagram showing a first embodiment of a projection display device according to the present invention. FIG. 2 is a plan view showing an example of the configuration of a projection display device using a conventional reflective liquid crystal panel. FIG. 3 is a plan view showing an example of the configuration of a composite prism used in a projection display device according to the present invention. FIG. 4 is a spectral reflection characteristic diagram showing an example of the characteristics of the blue light reflecting surface in the composite prism. FIG. 5 is a spectral reflection characteristic diagram showing an example of the characteristics of the red light reflecting surface in the composite prism. FIG. 6 is a plan configuration diagram showing a second embodiment of the projection type display device according to the present invention. FIG. 7 is a perspective view showing a third embodiment of the projection display device according to the present invention. FIG. 8 is a sectional view showing the configuration of a reflective liquid crystal light valve used in the third embodiment of the projection display device according to the present invention. Light Source Lamp Polarizer Projection Lens Complex Prism Reflective Liquid Crystal Panel Blue Light Reflective Dielectric Multilayer Red Light Reflective Dielectric Multilayer Above Figure 2 Figure 5 Figure 6 Figure 2 Figure 4 Figure 7 Figure 8 figure

Claims (2)

[Claims] (1) Mainly a white light source device, a color light separation/combiner that serves both color light separation and color light synthesis, a reflective liquid crystal light valve corresponding to each of the three primary color lights, and a lens that projects the luminous flux modulated by the liquid crystal light valve. In the projection type liquid crystal display device, the color light separation/synthesizer is a composite prism having at least two dichroic color light separation surfaces, and two of the three primary color lights separated or combined by the composite prism are A projection type liquid crystal display device characterized in that one color is reflected twice within a composite prism, and one color is not reflected once, and the optical path lengths for each of the three primary colors are equal. (2) The composite prism is composed of two triangular prisms, one quadrangular prism, and two dichroic color light separation surfaces, and the angle at which the white light incident on the composite prism first enters the dichroic surface where the colors are separated is The angle at which the light flux transmitted through the dichroic surface is incident on the dichroic surface to be color separated is 10 to 17 degrees, and the light flux reflected by each dichroic surface is between the glass material and the air. 2. The projection type liquid crystal display device according to claim 1, wherein the light is emitted after being reflected again by an optically flat surface that is an interface between the two.