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Multicolor Parallel-Oriented Nematic Liquid Crystal Displays Using Optical Compensation Films

IP.com Disclosure Number: IPCOM000120565D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Ong, HL: AUTHOR

Abstract

Disclosed is a parallel-oriented nematic color liquid crystal display (LCD) using optical compensating films to improve the contrast ratio, viewing angle, gray scale performance, and coloration characteristics.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Multicolor Parallel-Oriented Nematic Liquid Crystal Displays Using
Optical Compensation Films

      Disclosed is a parallel-oriented nematic color liquid
crystal display (LCD) using optical compensating films to improve the
contrast ratio, viewing angle, gray scale performance, and coloration
characteristics.

      In the presently disclosed LCD geometry, optical compensating
films are used to improve the optical performance of a
parallel-oriented nematic LCD.  The device geometry is defined as
follows: a general parallel nematic liquid crystal (LC) cell of
thickness d is confined between the planes z = 0 and z = d of
a Cartesian coordinate system. Both surfaces are treated to give a
homogenous alignment with a pretilt angle RS,LC defined with respect
to the surface, which is the xy plane.  The LC director is confined
to the xz plane.  Let no,LC and ne,LC be, respectively, the ordinary
and extraordinary indices of refraction for the LC. The LC's
birefringence is defined as WnLC = ne,LC - no,LC . Two polarizers are
attached; one polarizer is placed in front and the other behind the
panel.  In the presently disclosed LCD geometry, an optical
compensating film is placed between one of the polarizers and the LC
cell (either between the front polarizer and the LC cell or between
the rear polarizer and the LC cell).  Let no,CF and ne,CF be,
respectively, the ordinary and extraordinary indices of refraction
for the compensation film.  The film's birefringence is defined as
WnCF = ne,CF - no,CF .

      In the first geometry, the optical compensation film is made of
material or opposite birefringence (WnCF has a different sign than
WnLC) with the optical axis RS,CF tilted about the same angle as the
LC, RS,CF N RS,LC .  The thickness of the compensation film is chosen
such that dCF x WnCF N - dLC x WnLC .  This is done to
compensate for the difference in the birefringence and to obtain
uniform transmittance of light of different colors which passes
through the exit polarizer.  Various birefringence films can be used
for this device, such as a unidirectionally stretched polyester film,
or a uniaxially drawn polycarbonate...