Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1990-11-16
1993-03-16
Sikes, William L.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 63, 359 68, 359 93, G02F 1133
Patent
active
051949750
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a liquid crystal display device suitable for a high density display.
2. Background Technique
A super twist device has been known to obtain a high density dot matrix display by increasing a twist angle of liquid crystal molecules between electrodes to thereby cause a steep change in transmittance vs. voltage curve (T. J. Scheffer and J. Nehring, Appl., Phys., Lett. 45 (10) 1021-1023 (1984)).
In the above-mentioned technique, however, the value of the product .DELTA.n.multidot.d of the birefringence .DELTA.n of liquid crystal molecules in a liquid crystal display device and the thickness d of the liquid crystal layer was substantially in a range of 0.8-1.2 .mu.m (Japanese Unexamined Patent Publication No. 10720/1985), and a good contrast ratio could not be obtained unless a specified combination of hue such as yellowish green and dark blue, bluish purple and pale yellow and so on was used as a display color.
In the conventional liquid crystal display device, it was impossible to obtain a multicolor display or a fullcolor display by combining it with a multicolor filter because the conventional technique could not provide a monochrome (black and white) display.
On the other hand, there was proposed a system which utilized the similar system and was obtainable a display close to a monochrome display by determining the product .DELTA.n.multidot.d of the birefringence of the liquid crystal and the thickness to be small as about 0.6 .mu.m (M. Schadt et al, Appl. Phys. Lett. 50 (5), 1987, p. 236).
However, the proposed system had such disadvantages that it was dark; the greatest contrast ratio is not so large and the display had a bluish color so that clearness in display was poor.
There was proposed a system to realize a liquid crystal display device capable of displaying a monochrome display and having a high contrast ratio that two liquid crystal cells which have opposite helical sense each other are placed on one another wherein a voltage is applied to either cell and the other cell is merely used as an optical compensation plate (Report of Television Association 11 (27), p. 79, (1987) by Okumura et al., J. J. A. P., 26 (11), L1784 (1987) by Kato et al). However, the proposed system has such drawbacks that the matching of the product .DELTA.n.multidot.d between the two overlaid cells was very severe, hence, it was difficult to improve yield and the characteristic feature to produce a thin and light liquid crystal cell was sacrificed because it was necessary to overlay two liquid crystal cells.
Further, there was a proposal that a film stacked type liquid crystal display device for a monochrome display wherein one of the two overlaid cells was replaced by a uniaxial birefringent film (Japanese Unexamined Patent Publication No. 271415/1988).
As the above-mentioned uniaxial birefringent film, a uniaxial birefringent film having the optical axis in its film plane is generally used. Namely, the generally used uniaxial birefringent film has a nature of n.sub.x >n.sub.y =n.sub.z wherein n.sub.x, n.sub.y and n.sub.z represent three main refractive indices where n.sub.x and n.sub.y represent the refractive indices in the direction of film plane (provided n.sub.x >n.sub.y) and n.sub.z represents the refractive index in the direction Of film thickness.
In the film stacked type liquid crystal display device of the above-mentioned system which used the uniaxial birefringent film having the optical axis in its film plane in order to effect the compensation of the liquid crystal cell, it had disadvantages that a display was colored when it was viewed from an oblique direction, or black and white tones are inversed. Accordingly, it was difficult to produce, with high yield, a liquid crystal display device which has high brightness, good black and white characteristic and a wide viewing angle.
The liquid crystal display device having a bright, black and white display and having a wide viewing angle can realize a monocolor, a multicolor or fullcolor display
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Akatsuka Minoru
Sawada Kazutoshi
Sohda Yuji
Asahi Glass Company Ltd.
Duong Tai V.
Sikes William L.
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