Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1989-06-26
1992-06-02
Miller, Stanley D.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 63, G02F 1133
Patent
active
051192209
DESCRIPTION:
BRIEF SUMMARY
TITLE OF THE INVENTION
The present invention relates to liquid crystal display devices which are suitable for use in high level multiplexing drives providing a display which is easy to see.
DESCRIPTION OF THE BACKGROUND ART
Recently, field-effect type liquid crystal display devices having a twisted structure of liquid crystal molecules have been developed, which provide a wide range of high contrast (namely, a wide visual range) and which enabled high level multiplexing drive. In such liquid crystal display devices, liquid crystal molecules are oriented with a twist angle of 180.degree. to 360.degree. and a liquid crystal layer is placed between two polarizers. One of such liquid crystal display devices is disclosed for example in EPO-0131216 A3. In such a liquid crystal display device, the display color appears bluish or yellowish due to birefringence of the liquid crystal.
On the other hand, if two liquid crystal panels are provided one upon another for phase compensation as disclosed for example in U.S. Pat. No. 4,443,065, the background color can be made close to white.
The principle of the method of U.S. Pat. No. 4,443,065 will be briefly described. The hue observed due to birefringence of the liquid crystal is an interference color, which appears because a beam is elliptically polarized in a liquid crystal layer. Consequently, an achromatic color can be obtained by twisting back the once twisted beam. For this purpose, a liquid crystal panel having the same characteristics as a liquid crystal panel used for driving is placed thereon, whereby the liquid crystal panel is used for achromatization (compensation).
However, since such liquid crystal panels include two liquid crystal cells placed one upon another, the entire body of the display device becomes thick, which unfavorably causes a shadow or remote-appearing image or a change in contrast due to parallax (dependent on the observing direction). Further, such liquid crystal panels have a large number of pixels because they are suited for a high level multiplexing drive, and accordingly have a large display area. In addition, since the interference color depends also on the thickness of a liquid crystal layer, a strict control is required for attaining a uniform thickness of the liquid crystal layer and stable characteristics over a wide area. As a result, the manufacturing efficiency is lowered and the manufacturing costs are increased.
On the other hand, in order to adjust the hue in a liquid crystal display device, the method of using a 1/4 wavelength plate or a phase plate is conventionally used as disclosed for example in U.S. Pat. No. 4,232,948 or Japanese Patent Laying-Open No. 600/1980. However, although coloring and achromatization are simply regarded as being based on opposite theories, it is practically difficult to effect achromatization by circular polarization or using a 1/4 wavelength plate. This is so because a liquid crystal layer has complicated light transmitting characteristics although a wavelength plate (.lambda. plate) has effects on specified wavelengths of light. Further, it is difficult to adjust the optical characteristics of the wavelengths plate and of the liquid crystal layer since the quality of display is lowered if the liquid crystal layer does not have stable characteristics over a wide display area. Therefore, phenomena such as the appearance of an other interference color, of a darkened display or a lowered contrast occur. These phenomena unfavorably lower the quality of the display.
There has been proposed another technique which uses a uniaxially stretched film which is polarized as for use in a liquid crystal display device, as disclosed, for example, in Japanese Patent Laying-Open No. 192014/1988 describing the following technique. Since an interference color is liable to appear if a support film is attached to a polarizing film, the polarizing axis and the stretching direction are made to coincide in order to prevent an interference. Accordingly, an already caused interference color of an optical body canno
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Narita Kenichi
Suzaki Takeshi
Duong Tai V.
Fasse W. G.
Kane, Jr. D. H.
Miller Stanley D.
Sanyo Electric Co,. Ltd.
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