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HIGH-SPEED FERROELECTRIC LIQUID DEVICES WITH OPTIMAL COUPLING OF FIELD AND POLARIZATION

IP.com Disclosure Number: IPCOM000026766D
Original Publication Date: 1993-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 4 page(s) / 154K

Publishing Venue

Xerox Disclosure Journal

Abstract

In many applications, such as optical shutters and print-bars, it is frequently desirable to modulate the optical properties of the liquid crystal by externally controlled means. Electro-optical effects of ferroelectric liquid crystals are obtained through the coupling of externally applied electric field, E, to the spontaneous polarization, P. This coupling gives rise to a torque, T, equal to the vector product of E and P, which rotates the polarization and hence the molecular director, n, as n and P are always orthogonal to each other. The relations of E, P, n and T are shown in Figure 1. The magnitude of T determines, for a given material and temperature, the rotational speed. In the most common application of this electro-optical effect, the liquid crystal is encapsulated in a flat cell made of electroded glass plates. This flat field geometry more or less confines E in the direction normal to the plates. The small component that is off normal, due to the anisotropic character of the liquid crystal can be neglected for most purposes. Sometimes electrodes that can generate in-plane fields are sandwiched between the plates. Nevertheless, as long as the direction of E is fixed in space and P is rotating, there will be a situation in which their coupling is zero. Furthermore, the magnitude of T is not always at the maximum. Under such circumstances, the cell will not switch at the fastest speed that it, in principle, could for a given field. To remedy this deficiency, we propose to drive the ferroelectric liquid crystals with a rotating field obtained as the resultant field of multiple electrode pairs in appropriate phase relationships. When this field is kept orthogonal to the polarization, maximal torque results at all times and the cell switches at full speed.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

HIGH-SPEED FERROELECTRIC Proposed Classification LIQUID DEVICES WITH OPTIMAL
COUPLING
OF FIELD AND
POLARIZATION
Sui-Kong Hark
Joseph J.
Wysocki
Virgil J. Hull

U.S. C1.354/241 Int. C1. G03b 9/28

FIG. I

X

8 v2coso t

FIG. 2

I I

Vlsinot

XEROX DISCLOSURE JOURNAL - Vol. 18, No. 4 July/August 1993 377

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

Page 2 of 4

HIGH-SPEED FERROELECTRIC LIQUID DEVICES WITH OPTIMAL COUPLING OF FIELD AND POLARIZATION (Cont'd)

E<

1,

ot=O

ot = n/2

P

FIG. 3B

ot = (3n)/2

mt=n

FIG. 30

378 XEROX DISCLOSURE JOURNAL - Vol. 18, No. 4 July/August 1993

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

Page 3 of 4

HIGH-SPEED FERROELECTRIC LIQUID DEVICES WITH OPTIMAL COUPLING OF FIELD AND POLARIZATION (Cont'd)

In many applications, such as optical shutters and print-bars, it is frequently desirable to modulate the optical properties of the liquid crystal by externally controlled means. Electro-optical effects of ferroelectric liquid crystals are obtained through the coupling of externally applied electric field, E, to the spontaneous polarization, P. This coupling gives rise to a torque, T, equal to the vector product of E and P, which rotates the polarization and hence the molecular director, n, as n and P are always orthogonal to each other. The relations of E, P, n and T are shown in Figure 1. The magnitude of T determines, for a given material and temperature, the rotational speed. In the most common application of this electro-optical effect, the liquid crystal is encapsulated in a flat cell made of electroded glass plates. This flat field geometry more or less confines E in the direction normal to the plates. The small component that is off normal, due to the anisotropic character of the liquid crystal can be neglected for most purposes. Sometimes electrodes that can generate in-plane fields are sandwiched between the plates. Nevertheless, as long as the direction of E is fixed in space and P is rotating, there will be a situation in which their coupling is zero. Furthermore, the magnitude of T is not always at the maximum. Under such circumstances, the cell will not switch at the fastest speed that it, in principle, could for a given field. To remedy this deficiency, we propose to drive the ferroelectric liquid crystals with a rotating field obtained as the resultant field of multiple electrode pairs in appropriate phase relat...