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IMPROVED OPERATION OF MULTI-PLEXED FERROELECTRIC LIQUID CRYSTAL IMAGE BARS

IP.com Disclosure Number: IPCOM000025830D
Original Publication Date: 1988-Jun-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 218K

Publishing Venue

Xerox Disclosure Journal

Abstract

Ferroelectric liquid crystals (FLCs) have high potential for use in displays, image bars, and shutters because these materials operate at higher speeds than conventional materials do; they are bi-stable and offer the possibility of highly multiplexed devices; and they are polar and their operation thus depends upon the sign of applied voltage. A potential disadvantage of these materials is that the threshold for switching does not depend upon voltage alone but upon the product of voltage and its duration. Thus, in multiplexed systems where non-addressed elements are subjected to cross talk, these elements may turn on partially, or even fully, if the cross talk has a voltage-duration product above a threshold value. In some materials, the threshold value is so low that it is difficult to address elements without affecting non-addressed ones, thereby restricting severely the degree of multiplexibili ty.

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Page 1 of 4

(EROX DISCLOSURE JOURNAL

IMPROVED OPERATION OF MULTI- PLEXED FERROELECTRIC LIQUID U.S. C1.350/160 CRYSTAL IMAGE BARS
Joseph J. Wysocki
Sui-Kong Hark
V. Joseph Hull Joseph F. Stephany

Proposed Classification Int. C1. G02f 1/28

TRANSMISSION OF FERROELECTRIC LIQUID CRYSTAL CELL BETWEEN CROSSED POIARIZERS

1

.8

.6

TRANSMISSION (T)

.4

.2

0

0 5 10 15 20 25 30 35 40 45

OPTICAL TILT ANGLE (e)

(DEGREES)

Volume 13 Number 3 May/June 1988 135

[This page contains 1 picture or other non-text object]

Page 2 of 4

IMPROVED OPERATION OF MULTI-PLEXED FERROELECTRIC LIQUID CRYSTAL IMAGE BARS (Cont'd)

Ferroelectric liquid crystals (FLCs) have high potential for use in displays, image bars, and shutters because these materials operate at higher speeds than conventional materials do; they are bi-stable and offer the possibility of highly multiplexed devices; and they are polar and their operation thus depends upon the sign of applied voltage. A potential disadvantage of these materials is that the threshold for switching does not depend upon voltage alone but upon the product of voltage and its duration. Thus, in multiplexed systems where non-addressed elements are subjected to cross talk, these elements may turn on partially, or even fully, if the cross talk has a voltage- duration product above a threshold value. In some materials, the threshold value is so low that it is difficult to address elements without affecting non- addressed ones, thereby restricting severely the degree of multiplexibili ty.

A mode of operation is proposed which relaxes the threshold criterion and promises a higher degree of multiplexibility without severe loss of contrast, but with some loss in absolute light throughput. This mode is of principal use in image-bar applications where a non-linear detector, the photoreceptor, for example, is an integral part of the application. The mode is based upon the frequently observed dependence of the FLC tilt angle upon applied voltage. The tilt angle is typically small at zero applied voltage; it increases with voltage, saturating usually around 10 volts. Application of this tilt angle dependence in the proposed mode of operation is most easily described by an example. Consider a surface-stabilized device in which the helicoidal twist of the FLC is suppressed by closely spaced surfaces. Consider also that the device is operated at a voltage at which the tilt angle is saturated at its maximum value. The FLC molecules at the surface are constrained to one of two stable positions which are selectable by means of the applied voltage. The device incorporates a polarizer and an analyzer, the polarizer attached at an angle corresponding to one of the two surface-stabilized states and the analyzer at 90" to the polarizer direction. With the FLC in this stabilized state, no light passes through the cell. When the FLC is activated, however, the material is switched to the other surface-stabilized state, and light now passes through the device.

The...