JPH0634931A - Projection type display - Google Patents

Abstract

PURPOSE:To provide the compact projection display which uses a reflection type liquid crystal element. CONSTITUTION:In the projection type display consisting of a light source 1, a projection lens 7, and reflection type liquid crystal element 9, 10, and 11, the optical axis 21 of the light source 1 and the center axis 22 of the projection lens 7 are arranged in parallel to eliminate an unnecessary space in the whole optical system, thereby constituting the compact projection type display. Consequently, the compact projection type display can be constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type display for optically enlarging and displaying an image on a screen. In particular, it relates to a projection type display using a reflective liquid crystal element for image reproduction.

[0002]

2. Description of the Related Art Projection-type displays using liquid crystal elements have become popular in recent years because they are easier to handle than projection-type displays using CRTs (Cathod Ray Tubes). However, since the transmissive liquid crystal element has been used, there is a defect that the optical system becomes large. Therefore,
In order to realize a more compact projection type display, a projection type display using a reflection type liquid crystal element instead of a transmission type liquid crystal element is drawing attention.

Conventionally, regarding the construction of a projection optical system of a projection type display using a reflection type liquid crystal element, digest of S. ID 88, pages 102 to 10
Page 5 (Digest of SID88, pp102-105, 1
988) and the like. The configuration of the projection optical system of the conventional projection display will be described with reference to FIG. The main components of the projection optical system include a light source, a liquid crystal element and a projection lens. The projection light 120 generated by the light source 100 to which the parabolic mirror 101 and the fan 111 are attached passes through the cold filter 102, and then the projection light 120 is condensed on the mirror 104 by the condenser lens 103. Further, after being reflected by the mirror 104 and transmitted through a part of the projection lens 105, it is incident on a reflective liquid crystal element mounted around the dichroic prism 106 and is further reflected. The reflected light again passes through the dichroic prism 106 and is projected by a projection lens 105 onto a screen (not shown). The entire optical system is covered by a housing 110. As described above, the central axis 122 of the projection lens 105 and the optical axis 121 of the light source 100 are orthogonal to each other.

[0004]

Generally, in the projection type display as described above, a metal halide lamp or the like is used as a light source. The metal halide lamp is suitable as a light source for a projection display because it has high luminous efficiency and good color rendering. However, since the discharge lamp has a long lamp length, it is necessary to provide a vacant space before and after the lamp as a measure against a high voltage during lighting. For this reason, as shown in FIG. 2, when the lamp is arranged at a right angle to the central axis of the projection lens, the lateral extension of the projection lens becomes large depending on the length of the lamp. As a result, the projection type display becomes large in size, which hinders its portability.

An object of the present invention is to provide a compact projection type display having high portability.

[0006]

The object of the invention is achieved by arranging the central axis of the projection lens and the optical axis of the lamp in parallel.

[0007]

In general, in a projection type display using a light valve such as a liquid crystal element, an image reproduced by the liquid crystal element is optically enlarged and displayed on the screen. At this time, it is necessary to correct various inspections of the projection lens in order to reproduce a clear image on the screen. For this reason, the length of the projection lens becomes longer than the diameter of the projection lens. In some cases, it will be 2 to 3 times. On the other hand, the metal halide lamp used as the light source has a long lamp length as described above. For example, input power 150
With a watt metal halide lamp, the lamp diameter is about 10
While the lamp length is about 90 mm, the lamp length is about 90 mm. Furthermore, since a high voltage is applied at the start of lighting, it is necessary to provide a gap between the electrode end and the cover of the light source section. From the above, a space larger in the length direction than the diameter direction of the metal halide lamp is required. If the center axis of the projection lens and the optical axis direction of the metal halide lamp are made parallel, a long metal halide lamp can be arranged next to the long projection lens.
Therefore, a vacant space is eliminated and the size of the entire optical system is reduced, so that a compact projection display can be realized.

[0008]

Embodiments of the present invention will be described in detail below with reference to the drawings. The optical system of the projection type display is composed of a light source, a projection lens, a liquid crystal element as a light valve, other optical elements, and a housing covering them. Figure 1
1 shows a configuration of an optical system of a projection display according to the present invention. The light source 1 is provided with a reflecting mirror 2 for efficiently using light and a fan 12 for cooling. The dichroic filter of the reflecting mirror 2 reflects only the visible light generated by the light source 1 and removes the infrared light portion. The reflecting mirror 2 is a parabolic mirror, and the light emitting point of the light source 1 is arranged at the focal position thereof. As a result, the projection light 20 generated by the light source 1 and reflected by the reflecting mirror 2 becomes parallel light. The projection light 20 is reflected by the cold mirror 3. The infrared light remaining in the projection light 20 is further removed by the cold mirror 3 and the filter 4. The filter 4 further absorbs and removes the ultraviolet light included in the projection light 20. As the filter 4, a combination of an infrared light absorbing plate or an infrared light reflecting plate and an ultraviolet light absorbing plate is used. The projection light 20 is condensed on the small reflective optical element 6 by the condenser lens 5. The reflective optical element 6 is installed in the projection lens 7. The projection lens 7 is composed of two large projection lens groups 7a and 7b.

The reflective optical element 6 is composed of a plane mirror or a prism. A plane mirror is a transparent substrate such as soda glass or quartz glass or an opaque substrate such as ceramics on which a metal thin film such as aluminum or chromium is formed, or a metal such as aluminum is polished, and if necessary, a metal thin film is further formed and reflected. Those having an improved rate, or those having a dielectric multilayer film formed on the above-mentioned transparent substrate are used. Since the plane mirror can be made thin, it can be easily arranged and is inexpensive and easy to use. In addition, since the polished metal has a high thermal conductivity, it is easy to take measures against the temperature rise that occurs when the high-intensity projected light is condensed. The prism is
A glass such as soda glass or quartz glass that has been polished, and has a reflectance improved by forming a reflective film such as a metal thin film as needed is used. This reflective optical element is provided with a radiator if necessary in order to prevent the temperature from rising due to the irradiation of the high-intensity projection light condensed by the condenser lens. Projection light 20 reflected by the reflective optical element 6
Is collimated by the projection lens group 7 a and is incident on the dichroic prism 8. The reflection-type liquid crystal elements 9 and 1 are provided on the three exit side surfaces of the dichroic prism 8.
0 and 11 are attached respectively. Projection light 20
Is divided by the dichroic prism 8 into light in the wavelength bands of red, green and blue which are the three primary colors of light. The dichroic prism is formed by bonding four glass blocks together, and a dielectric multilayer film that selectively reflects light in a wavelength band corresponding to red among visible light wavelengths is formed on the bonding surface 8a. Therefore, the light reflected by the bonding surface 8a is applied to the reflective liquid crystal element 9 that reproduces a red image. Also,
A dielectric multilayer film that selectively reflects light in a wavelength band corresponding to blue among visible light wavelengths is formed on the bonding surface 8b. Therefore, the light reflected by the bonding surface 8b is applied to the reflective liquid crystal element 11 that reproduces a red image. Light in the wavelength band corresponding to green of the wavelength of visible light is not reflected by any bonding surface and is transmitted as it is to the reflective liquid crystal element 10 which reproduces a green image. At this time, the optical axis of the light entering each reflective liquid crystal element is slightly inclined. The split light is reflected by the reflective liquid crystal element.
At this time, the image information is taken into each divided light in the form of light intensity modulated by each reflective liquid crystal element. After being reflected, the projected light becomes white light due to the joint surface of the dichroic prism 8 described above, but the optical path of the reflected light is different from the optical path of the incident light due to a slight tilt of the optical axis. The tilt angle is selected according to the size of the optical system,
Angles of between approximately 0.1 and 10 degrees are preferred. As a result, the projection light 20 that has become white light is condensed by the projection lens group 7a described above, not on the reflective optical element 6 but on the opening of the aperture 12. The projection light 20 that has passed through the aperture 12 enters the projection lens group 7b while spreading, and is projected on a screen (not shown) to display a magnified color image.

As the reflective liquid crystal element, a thin film transistor having a reflective electrode, a non-linear two-terminal element (MIM, etc.) glass substrate, or a single crystal silicon substrate having a MOS transistor formed thereon is provided between a transparent glass substrate and an opposing transparent glass substrate. , A polymer-dispersed liquid crystal, a smectic A liquid crystal, a cholesteric / nematic liquid crystal or other scattering liquid crystal, or a phase-controlled nematic liquid crystal or other liquid crystal layer is formed. Further, a matrix type liquid crystal element having no active element is also used for the pixel.

Further, it goes without saying that a light modulation element other than the liquid crystal element, for example, a solid element such as PLZT, a modulation element by a combination of a foil electrode and an oil film, or the like can be used.

The above-mentioned three reflective liquid crystal elements 9,
Silicon gel having a refractive index equal to that of glass, which is a material for the windows of the dichroic prism and the reflection type liquid crystal element, is injected between 10, 11 and the dichroic prism 8 to reflect the surface of the window material of the dichroic prism and the reflection type liquid crystal element. Is eliminated or reduced. Alternatively, an antireflection film is formed on the surface of the window material of the dichroic prism and the reflective liquid crystal element to remove or reduce surface reflection. The antireflection film may be for white light, or may be for the wavelength of each split projection light.

The optical system of the projection display described above is covered by the housing 14 except for the screen. In the optical system of the projection display described above, the central axis 22 of the projection lens 7 and the optical axis 2 of the metal halide lamp 1
Arrange so that 1 is parallel. By adopting this parallel arrangement, the size of the housing 14 that covers the optical system is reduced. Compared with the arrangement of FIG. 2, the size can be reduced to about 60%. Therefore, it is possible to realize a compact projection display which is more portable than before.

By using only one reflection type liquid crystal element without using a dichroic prism, a more compact projection type display for monochrome display can be realized. Furthermore, by forming a color filter on a glass substrate that serves as a window material for the reflective liquid crystal element, a single reflective liquid crystal element can display a color image without using a dichroic prism.

Although a metal halide lamp is used as a light source in this embodiment, it is obvious that the present invention can be applied to other discharge type lamps such as a xenon lamp and a mercury lamp. Further, it can be applied to a lamp using a filament such as a tungsten / halogen lamp.

[0016]

According to the present invention, it is possible to realize a compact projection type display excellent in portability.

[Brief description of drawings]

FIG. 1 is a configuration of an optical system of a projection display according to the present invention.

FIG. 2 is a configuration of an optical system of a projection type display of a conventional example.

[Explanation of Codes] 1 ... Light source, 2 ... Reflecting mirror, 3 ... Cold mirror, 4 ... Cold filter, 5 ... Condenser lens, 6 ... Reflective optical element, 7 ... Projection lens, 8 ... Dichroic prism,
9, 10, 11 ... Reflective liquid crystal element, 12 ... Aperture,
13 ... Fan, 14 ... Housing, 21 ... Optical axis of light source, 22 ...
The central axis of the projection lens.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Omura 4026 Kujimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Co., Ltd. Inside Hitachi Media Media Research Laboratories

Claims (1)

[Claims] 1. A projection type display comprising a light source, a projection lens and a liquid crystal element, wherein the optical axis of the light source and the central axis of the projection lens are arranged substantially parallel to each other.