Apparatus for and method of operation of smectic liquid crystal light valve having scattering centers

• US 5,140,448 A
• Filed: 10/24/1990
• Issued: 08/18/1992
• Est. Priority Date: 10/24/1990
• Status: Expired due to Fees

• Current Assignee: Transamerica Business Credit Corporation (Aegon Ltd.)
• Original Assignee: Greyhawk Systems, Inc.
• Inventors: Slobodin, David E., Bone, Matthew, Stefanov, Michael, Haven, Duane A., Kahn, Frederic J.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): TRICE, RONALD
• Application Number:
  US07/602,505
• Time in Patent Office: 664 Days
• Field of Search: 350/342, 350/346.4 S, 359/724 S, 359/904 S, 359/100.4 S, 359/43, 359/44, 359/45
• US Class Current: 349/166
• CPC Class Codes: G02F 1/135 Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied G02F1/133348 takes precedence

Abstract

A liquid crystal light valve, comprising a layer of liquid crystal for storing image information and a photoconductor aligned with the liquid crystal and positioned in closed proximity thereto for effecting an electric field applied across the liquid crystal. Apparatus is provided for simultaneously applying an electric field across the liquid crystal and photoconductor while impinging optical image information on the photoconductor, the photoconductor and applied field combining to produce a modified electric field across the liquid crystal which impresses the image information on the photoconductor into the liquid crystal.

Claims

1. A liquid crystal light valve apparatus comprising:

a layer of liquid crystal for storing image information, said liquid crystal being of the type which can have scattering centers;

means for creating ian initial optical density in said liquid crystal by forming scattering centers, said creating means including

means for applying a thermal pulse to said liquid crystal layer to raise the temperature thereof through the nematic-isotropic transition, and

means for cooling said liquid crystal layer through the nematic-isotropic transition to produce scattering centers in said liquid crystal layer;

photoconductor means aligned with said liquid crystal and positioned in close proximity thereto, said photoconductor varying an electric field applied across said liquid crystal in proportion to the amount of light impinging the photoconductor;

means for applying an electric field across said liquid crystal and photoconductor when said liquid crystal layer has scattering centers; and

means for impinging optical image information on said photoconductor, simultaneous to said application of said electric field across said liquid crystal and photoconductor, said photoconductor and applied field combining to produce a modified electric field across said liquid crystal which clears scattering centers in proportion to the image information so that said image information is impressed in said liquid crystal.

2. The apparatus of claim 1 wherein said means for impinging optical image information comprises means for optically addressing a light source in parallel.

3. The apparatus of claim 1 wherein said means for impinging optical image information comprises means for optically addressing a light source in series.

4. The apparatus of claim 1 wherein said liquid crystal is smectic A liquid crystal.

5. The apparatus of claim 1 wherein said liquid crystal includes a scattered background which blocks light before said impinging means impinges optical image information of said photoconductor.

6. The apparatus of claim 5 wherein said modified electric field comprises an electric field having values at least as great as a certain threshold value required to partially erase said scattering background which blocks light to a clear background, said certain threshold value occurring across said liquid crystal where optical energy from said optical image information has been impinged on a corresponding location on said photoconductor.

7. A liquid crystal light valve apparatus, comprising:

a layer of liquid crystal for storing image information, said liquid crystal being of the sort which can have scattering centers;

means for creating an initial optical density in said liquid crystal by forming scattering centers, said creating means including

means for applying a thermal pulse to said liquid crystal layer to raise the temperature thereof through the nematic-isotropic transition, and

means for cooling said liquid crystal layer through the nematic-isotropic transition to produce scattering centers in said liquid crystal layer, said creating means forming a background which blocks light by forming scattering centers in said layer of liquid crystal material;

photoconductor means aligned with said liquid crystal and positioned in close proximity thereto, said photoconductor spatially varying a magnitude of an electric field applied across said liquid crystal in proportion to the amount of light impinging the photoconductor;

means for applying a uniform electric field across said liquid crystal and photoconductor when said liquid crystal has scattering enters; and

means for impinging spatially varying optical image information on said photoconductor, simultaneous to said application of said uniform electric field, said photoconductor and said applied field combining to apply a spatially varying electric field across said liquid crystal to change said scattering background to a spatially varying clear background where said electric field has increased above a threshold value to impress said image information in said liquid crystal.

8. The apparatus of claim 7 wherein said liquid crystal material is smectic A liquid crystal.

9. A method of operating a liquid crystal light valve, comprising the steps of:

providing a layer of liquid crystal for storing image information, said liquid crystal being of the sort which can have scattering centers;

creating an initial optical density in said liquid crystal by forming scattering centers, said creating step including

applying a thermal pulse to said liquid crystal layer to raise the temperature thereof through the nematic-isotropic transition, and

cooling said liquid crystal layer through the nematic-isotropic transition to produce scattering centers in said liquid crystal layer;

aligning a photoconductor with said liquid crystal and positioning said photoconductor in close proximity thereto, said photoconductor varying an electric yield applied across said liquid crystal in proportion to the amount of light impinging the photoconductor;

applying an electric field across said liquid crystal and photoconductor when said liquid crystal has scattering centers; and

impinging optical image information on said photoconductor, simultaneous to applying said electric field across said liquid crystal and photoconductor, said photoconductor and applied field combining to produce a modified electric yield across said liquid crystal which clears scattering centers in proportion to the image information so that said image information is impressed in said liquid crystal.

10. A method of producing a spatially varying optical density in a liquid crystal light valve apparatus which includes a liquid crystal layer of the sort which can have scattering centers, said method comprising the steps of:

creating an initial optical density in said liquid crystal light valve by forming scattering enters in said liquid crystal layer, said creating step including

applying a thermal pulse to the liquid crystal layer to raise the temperature thereof through the nematic-isotropic transition, and

cooling the liquid crystal layer through the nematic-isotropic transition to produce scattering centers in the liquid crystal layer; and

applying a spatially varying electric field to said liquid crystal layer in away which clears the scattering centers in proportion to the spatial variation of said electric field, to produce a corresponding spatially varying optical density.

11. The method of claim 10 wherein the initial optical density is spatially uniform.

12. The method of claim 10 wherein the step of applying a spatially varying electric field includes the steps of

applying a spatially uniform electric field across the liquid crystal layer and a photoconductor layer positioned in close proximity to the liquid crystal layer, and

simultaneously applying spatially varying optical image information to the photoconductor layer to spatially alter its impedance to produce a spatially varying field across said liquid crystal layer.

13. The method of claim 10 wherein said liquid crystal material is Smectic A.

14. The method of claim 13 wherein the step of applying a spatially varying electric field occurs when the liquid crystal layer is in the smectic state.

15. The method of claim 10 wherein the spatially varying electric field creates an optical density which ranges from scattering to completely clear and includes intermediate values.

16. A liquid crystal light valve apparatus, comprising:

a layer of liquid crystal for storing image information, said liquid crystal being of the sort which can have scattering center;

means for creating a uniform optical density in said liquid crystal light valve by forming scattering centers in said layer of liquid crystal material, said creating means including

means for applying a thermal pulse to the liquid crystal layer to raise the temperature thereof through the nematic-isotropic transition, and

means for cooling the liquid crystal layer through the nematic-isotropic transition to produce scattering centers in the liquid crystal layer;

photoconductor means aligned with said layer of liquid crystal and positioned in close proximity thereto for spatially modulating a magnitude of an electric field applied across said layer of liquid crystal in proportion to the amount of light impinging the photoconductor;

means for applying a uniform electric field across said layer of liquid crystal and photoconductor when said liquid crystal is provided with scattering centers; and

means for impinging optical image information which spatially varies in illumination intensity onto said photoconductor, simultaneous to said application of said uniform electric field, said photoconductor and said applied field combining to apply an electric field which spatially varies in magnitude across said liquid crystal to change said uniform optical density to a spatially varying optical density which can vary in degree of optical density from scattering to completely clear, including intermediate values, in proportion to the image information, by clearing scattering centers in said liquid crystal layer.