Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1989-06-06
1992-08-04
Hille, Rolf
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 63, 359 73, 359 93, 359 96, G02F 113
Patent
active
051364069
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a liquid crystal display device for a high density display.
BACKGROUND TECHNOLOGY
A super twist element has been known to obtain a high density dot matrix display by increasing a twist angle of liquid crystal molecules between both electrodes to thereby cause an acute change in voltage-transmittance characteristic (T. J. Scheffer and J. Nehring, Appl., Phys., Lett. 45 (10) 1021-1023 (1984)).
In accordance with the above-mentioned technique, a value of the product .DELTA.n.multidot.d of the birefingence .DELTA.n of liquid molecules in a liquid crystal display device and the thickness d of the liquid crystal layer is substantially within 0.8 .mu.m-1.2 .mu.m (Japanese Unexamined Patent Publication 10720/1985). Accordingly, a good contrast could not be obtained unless a specific combination in a display color such as yellowish green and dark blue, bluish purple and pale yellow and so on is used.
In the known-liquid crystal display device, it was impossible to obtain a multicolor display or a full color display by combining it with a microcolor filter because the conventional device could not effect a monochrome (black and white) display.
There is a proposed system to obtain a display close to a black and white display by determining the product .DELTA.n.multidot.d of the double refractive index of liquid crystal molecules and the thickness of the liquid crystal layer to be as small as nearly 0.6 .mu.m by using a technique similar to the above-mentioned technique (M. Schadt et al. Appl. Phys. Lett. 50(5), 1987, p.236).
However, the proposed technique had such disadvantages that a display is dark; the greatest contrast ratio is not large and the display has a bluish color so that clearness in display is poor.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display device capable of realizing a display close to a monochrome display, excellent viewing angle characteristics and a high contrast ratio.
It is another object of the present invention to provide a liquid crystal display device capable of realizing the same monocolor, multicolor or full color display as that effected by a conventional 90.degree. twisted nematic (TN) device by forming a fine color filter inside or outside the cell.
The foregoing and the other objects of the present invention have been attained by providing a liquid crystal display device comprising a first liquid crystal layer of a nematic liquid crystal having positive dielectric anisotropy and including a chiral material which is interposed between a pair of substrates each having an aligning layer which are arranged substantially in parallel, a voltage applying means to apply a voltage across transparent electrodes of the pair of substrates which interpose the first liquid crystal layer therebetween, a second liquid crystal layer of a nematic liquid crystal including a chiral material which is interposed between another pair of substrates each having an aligning layer, the second liquid crystal layer being adjacent to the first liquid crystal layer, and a pair of polarizing plates arranged outside the first and second liquid crystal layers, characterized in that the second liquid crystal layer contains dye; the product .DELTA.n.sub.1 .multidot.d.sub.1 of the anisotropy of refractive index .DELTA.n.sub.l of liquid molecules in the first liquid crystal layer and the thickness of the first liquid crystal layer d.sub.1 is in a range of 0.7-2.0 .mu.m; the axial direction of liquid crystal molecules of the first liquid crystal layer in an area close to the second liquid crystal layer is crossed at substantially a right angle to the axial direction of liquid crystal molecules of the second liquid crystal layer in an area close to the first liquid crystal layer; the twist angle of the liquid crystal molecules in the first liquid crystal layer is in a range of 200.degree.-300.degree.; the twist angle of the liquid crystal molecules in the second liquid crystal layer is substantially the same
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Akatsuka Minoru
Endo Yukiio
Kato Kazunori
Ohgawara Masao
Sawada Kazutoshi
Asahi Glass Company Ltd.
Hille Rolf
Tran Minhloan
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