US4927242A — Dual frequency, optically active liquid crystal c…

Claim 1

Independent Claim 205 words

A liquid crystal optical device comprising a liquid crystal panel including two opposed transparent base plates, each having at least one electrode disposed thereon, and a liquid crystal material sealed between the two base plates, said liquid crystal material having a dielectric anisoptropy which becomes zero at a crossing frequency ("fc") of 100 KHz or below at working temperatures, the dielectric anisotropy which being positive at frequencies lower than fc ("fl") and negative at frequencies higher than fc ("fh"), and a liquid crystal driving circuit for selectively applying signals of frequency fh and fl during successively repeating writing periods, T 1 , T 1 including a first signals applying period T 2 and a second signal applying period T 3 , such that T 1 =T 2 +T 3 , wherein the driving circuit selectively applies in T 2 a signal fl or a signal fh for placing the panel in one of the OFF or ON states, the liquid crystal material aligned parallel with an electric field or inclined with an electric field or inclined with respect to the electric field, and applies in T 3 a signal for placing the liquid crystal material in an initial driving state aligned with the electric field.

Claim 2

Dependent Claim 205 words

A liquid crystal optical device comprising a liquid crystal panel including two opposed transparent base plates, each having at least one electrode disposed thereon, and a liquid crystal material sealed between the two base plates, said liquid crystal material having a dielectric anisoptropy which becomes zero at a crossing frequency ("fc") of 100 KHz or below at working temperatures, the dielectric anisotropy which being positive at frequencies lower than fc ("fl") and negative at frequencies higher than fc ("fh"), and a liquid crystal driving circuit for selectively applying signals of frequency fh and fl during successively repeating writing periods, T 1 , T 1 including a first signals applying period T 2 and a second signal applying period T 3 , such that T 1 =T 2 +T 3 , wherein the driving circuit selectively applies in T 2 a signal fl or a signal fh for placing the panel in one of the OFF or ON states, the liquid crystal material aligned parallel with an electric field or inclined with an electric field or inclined with respect to the electric field, and applies in T 3 a signal for placing the liquid crystal material in an initial driving state aligned with the electric field.

Claim 3

Dependent Claim 295 words

A liquid crystal optical shutter comprising a liquid crystal panel including two opposed transparent base plates each having at least one electrode disposed thereon and a liquid crystal material sealed between the two base plates, said liquid crystal material including an optically active liquid crystal material and having a dielectric anisotropy which becomes zero at a crossing frequency ("fc") of 100 KHz or below at working temperatures, the dielectric anisoptropy being positive at a low frequency ("fl") lower than fc and negative at a high frequency ("fh") higher than fc, polarizers disposed on each side of said liquid crystal panel with the axis of polarization extending substantially perpendicular to each other, and liquid crystal driving circuit means for selectively applying signals of frequency fh and frequency fl during a repetitive period of time T 1 , T 1 including a first signal applying period T 2 and a second signal applying period T 3 such that T 1 =T 2 +T 3 , wherein the driving circuit selectively applies in T 2 a low frequency signal fl for placing the panel in the OFF condition with the liquid crystal material in an initial driving state aligned parallel to an electric field with no transmittance of incident light, or a high frequency signal fh and the liquid crystal material inclined with respect to the electric field for placing the panel in an ON condition with light transmittance and applied in T 2 a low frequency signal fl for placing the liquid crystal panel in the initial driving state, the base plates spaced apart a distance d and the liquid crystal material having a helical pitch so that the liquid crystal molecules are twisted between said plates at an angle of twist between 270° and 630° .

Claim 4

Dependent Claim 295 words

A liquid crystal optical shutter comprising a liquid crystal panel including two opposed transparent base plates each having at least one electrode disposed thereon and a liquid crystal material sealed between the two base plates, said liquid crystal material including an optically active liquid crystal material and having a dielectric anisotropy which becomes zero at a crossing frequency ("fc") of 100 KHz or below at working temperatures, the dielectric anisoptropy being positive at a low frequency ("fl") lower than fc and negative at a high frequency ("fh") higher than fc, polarizers disposed on each side of said liquid crystal panel with the axis of polarization extending substantially perpendicular to each other, and liquid crystal driving circuit means for selectively applying signals of frequency fh and frequency fl during a repetitive period of time T 1 , T 1 including a first signal applying period T 2 and a second signal applying period T 3 such that T 1 =T 2 +T 3 , wherein the driving circuit selectively applies in T 2 a low frequency signal fl for placing the panel in the OFF condition with the liquid crystal material in an initial driving state aligned parallel to an electric field with no transmittance of incident light, or a high frequency signal fh and the liquid crystal material inclined with respect to the electric field for placing the panel in an ON condition with light transmittance and applied in T 2 a low frequency signal fl for placing the liquid crystal panel in the initial driving state, the base plates spaced apart a distance d and the liquid crystal material having a helical pitch so that the liquid crystal molecules are twisted between said plates at an angle of twist between 270° and 630° .

Claim 5

Dependent Claim 32 words

The liquid crystal optical device of claim 1, wherein the liquid crystal material is a composition comprising an optically inactive nematic liquid crystal and an optically active liquid crystal material added thereto.

Claim 6

Dependent Claim 37 words

The liquid crystal optical device of claim 1, wherein the helical structure of the molecules of the liquid crystal composition sealed in said liquid crystal panel are twisted at an angle of twist of 270° to 990°.

Claim 7

Dependent Claim 18 words

The liquid crystal optical device of claim 4, wherein the angle of twist is between 270° and 630°.

Claim 8

Dependent Claim 34 words

The liquid crystal optical device of claim 1, wherein said two base plates have surfaces which have been treated to enable the liquid crystal molecules adjacent to said surface to be oriented parallel thereto.

Claim 9

Dependent Claim 21 words

The liquid crystal optical device of claim 1, wherein the two polarizers having polarizing axes extending substantially perpendicular to each other.

Claim 10

Dependent Claim 24 words

The liquid crystal optical device of claim 1, wherein the signal fl is applied for the entire writing period of time T 1 .

Claim 11

Dependent Claim 35 words

The liquid crystal optical device of claim 1, wherein the liquid crystal driving circuit further includes means for applying said signal of frequency of fl for an interval of time longer than one writing period.

Claim 12

Dependent Claim 22 words

The liquid crystal optical device of claim 1, wherein the distance between the opposed base plates is between 2 and 10 μm.

Claim 13

Dependent Claim 30 words

The liquid crystal optical device of claim 3, wherein the optically active material is present in the liquid crystal composition in an amount ranging from 0.5 to 10 weight percent.

Claim 14

Dependent Claim 80 words

An electronic reading device for activating a photosensor copying for an original image comprising a light source for illuminating the surface of the original, an array of liquid crystal light optical devices as defined in claim 1, converging light means for directing the illuminated image from the original to one side of the liquid crystal optical devices and photosensor means disposed on the opposed side of the liquid crystal optical devices for receiving the light transmitted by the optical devices.

Claim 15

Dependent Claim 60 words

A photoswitch for switching light signals comprising a plurality of optical shutter including liquid crystal optical devices as defined in claim 4, a plurality of optical fibers corresponding to the shutters disposed on one side of the shutters and a single optical fiber having an end disposed over the plurality of optical shutters on the opposite side of the shutters.

Claim 16

Dependent Claim 29 words

The liquid crystal optical device of claim 1, wherein the signal for placing the liquid crystal material in the initial driving state is the signal of low frequency fl.

Claim 17

Dependent Claim 22 words

The liquid crystal optical device of claim 1, wherein the liquid crystal material includes an optically active material for causing dielectric relaxation.

Claim 18

Dependent Claim 20 words

The liquid crystal optical device of claim 15 wherein the optically active material comprises a chiral nematic liquid crystal material.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1993-05-21	1993-11-20	1994-05-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1997-05-21	1997-11-20	1998-05-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2001-05-21	2001-11-20	2002-05-22	$7700.00	Window Closed / Lapsed

Dual frequency, optically active liquid crystal cell

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