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Apparatus Configuration and Liquid Crystal Display Operating Mode having High Transmission and High Contrast Ratio for Projection Display Application

IP.com Disclosure Number: IPCOM000118651D
Original Publication Date: 1997-May-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 6 page(s) / 130K

Publishing Venue

IBM

Related People

Howard, WE: AUTHOR [+2]

Abstract

To choose a proper Liquid Crystal Display (LCD) mode for reflective type projection display, (*) proposed a reflective 63 degrees Twisted Nematic-Electrically Controllable Birefringent (TN-ECB) mode using a reflective Twisted Nematic (TN) cell (a mirror was used) and a single polarizer. This configuration is a Normally Black (NB) mode, which is impossible to get good dark state for all three colors of light. In this document, a new apparatus configuration and new LCD operation mode are proposed for projection display application to achieve both high optical transmission and high contrast ratio.

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Apparatus Configuration and Liquid Crystal Display Operating Mode
having High Transmission and High Contrast Ratio for Projection Display
Application

      To choose a proper Liquid Crystal Display (LCD) mode for
reflective type projection display, (*) proposed a reflective 63
degrees Twisted Nematic-Electrically Controllable Birefringent
(TN-ECB) mode using a reflective Twisted Nematic (TN) cell (a mirror
was used) and a single polarizer.  This configuration is a Normally
Black (NB) mode, which is impossible to get good dark state for all
three colors of light.  In this document, a new apparatus
configuration and new LCD operation mode are proposed for projection
display application to achieve both high optical transmission and
high contrast ratio.

      The apparatus configuration using a polarizing beam splitter
and a reflective TN cell (operating in TN-ECB mode) is shown in Fig.
1.  In Fig. 1, no separate polarizer is used.  This configuration
is a Normally White (NW) mode, which, in principle, can achieve a
good dark state for three colors of light if applied voltage is high
enough.

      Fig. 2 shows the optimum transmission of the low-field state
(with operating voltage of 1V) of the configuration showed in Fig. 1
as a function of twist angle.  It indicates that twist angle of 64
degrees gives a highest optimum optical transmission.  The optimum
optical transmission decreases when the twist angle increases from 64
degrees toward 90 degrees.  Fig. 3 shows the optimal contrast ratio
(between operation voltages of 1V and 5V) as a function of twist
angle.  It indicates that optimal Contrast Ratio (CR) increases as
the twist angle increase from 60 degrees toward 90 degrees.  Figs. 2
and 3 tell us that there is a trade-off between optimal optical
transmission and the optimal CR for the twist angle between 60
degrees and 90 degrees.  We would not be able to obtain both high
optical transmission and high CR simultaneously with the
configuration given in Fig. 1.  However, if the configuration shown
in Fig. 1 is slightly modified with a proper optical compensator (a
birefringent film or slat)  placed between polarizing beam splitter
and the TN cell, we can obtain  both high optical transmissio...