Smectic liquid crystal devices using SSFLC and electroclinic effect based cells

• US 5,168,381 A
• Filed: 12/27/1990
• Issued: 12/01/1992
• Est. Priority Date: 10/30/1989
• Status: Expired due to Fees

• Current Assignee: University of Colorado System
• Original Assignee: University of Colorado System
• Inventors: Walba, David M.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/634,417
• Time in Patent Office: 705 Days
• Field of Search: 350/350 S, 350/340, 350/334, 350/337, 350/347 R, 350/335, 359/63, 359/39, 359/53, 359/84, 359/93, 359/94, 359/99, 359/100
• US Class Current: 349/77
• CPC Class Codes: G02F 1/13473 for wavelength filtering or for colour display without the use of colour mosaic filters
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals
• CPC Class Codes: G02F 2203/055 wavelength filtering

Abstract

Fast switching, high-contrast light valves and light valves which function for multi-level, gray-scale production are provided. Light valves of this invention employ two or more low-tilt, chiral smectic liquid crystal cells which are half-wave plates. Bistable FLC cells or FLC cells having smectic A* materials which display a field dependent tilt angle can be used. The FLC cells of exemplary device configurations are positioned sequentially along a light path through the device with the optic axes of the sequential FLC cells rotating in opposite directions upon application of a driving electric field thereacross. Light valves employing smectic C* and smectic A* liquid crystal cells are provided.

Claims

1. A light valve which is switchable, by application of an electric field, between a first and a second transmission state which comprises two or more chiral smectic liquid crystal cells aligned sequentially along a light path through said valve, said cells positioned between an entrance polarizer which defines the plane of polarization of light entering said valve and an exit polarizer, said cells being synchronously switchable between said transmission states, wherein said cells are half-wave plates, wherein said cells are oriented with respect to each other such that in said first transmission state the optic axes of all said cells are either parallel or perpendicular to each other and are either parallel or perpendicular to the plane of polarization of light entering said valve and in said second transmission state the optic axes of sequential cells along the light path through said light valve rotate in opposite directions and wherein switching between said two transmission states results in switching between a dark and a bright transmission state.

2. The light valve of claim 1 in which said chiral smectic liquid crystal cells are SSFLC cells.

3. The light valve of claim 1 in which said chiral smectic liquid crystal cells are electroclinic-effect based cells.

4. The light valve of claim 3 wherein the magnitude of the applied electric field to said electroclinic-effect based cells for switching to said second transmission state is that which si required to attain a tilt angle of 90°

/4n wherein n is the number of cells in said light valve and wherein said tilt angle is the tilt angle of each of the individual cells contained in said light valve.

5. The light valve of claim 3 in which said electroclinic-effect based cells are operated in a pseudo-bistable mode.

6. The light valve of claim 5 in which said electroclinic-effect based cells contain smectic A liquid crystal materials.

7. The light valve of claim 1 which contains two SSFLC cells wherein said tilt angle of each of said cells is about 22.5°

/2.

8. The light valve of claim 1 which contains four SSFLC cells wherein said tilt angle of each of said cells is about 22.5°

/4.

9. The light valve of claim 1 wherein the chiral smectic liquid crystal materials of sequential cells along the light path through said valve have opposite signs of polarization density.

10. The light valve of claim 1 wherein the sign of polarization of the chiral smectic liquid crystal materials in each cell is the same and wherein the electric field applied to said sequential liquid crystal cells along said light path alternates in sign.

11. The light valve of claim 1 wherein, in said first transmission state, the optic axes of said cells are parallel with respect to each other.

12. The light valve of claim 1 wherein, in said first transmission state, the optic axes of said cells are perpendicular with respect to each other.

13. A multistable gray-scale light valve which comprises two or more chiral smectic liquid crystal cells aligned along a light path through said valve between crossed or parallel polarizers, each of said cells being independently switchable between a switched and an unswitched sate by application of an electric field, wherein said cells are oriented with respect to each other such that, in the unswitched state, the optic axes of said cells are either parallel or perpendicular and, in the switched state, the optic axes of sequential cells along said light path through said light valve rotate in opposite directions on said application of an electric field, wherein the sum of the tilt angels of said cells is 22.5°

and wherein independent switching of said cells results in selection of device transmission states each of which device transmission states results in an output light polarization rotated by a given angle between about 0° and

about 90°

from the polarization of light entering said valve.

14. The multistable gray-scale light valve of claim 13 wherein the tilt angles of the chiral smectic liquid crystal cells in said light valve are continuous variable between about 1°

and about 11.25°

by application of a variable electric field.

15. The multistable gray-scale light valve of claim 14 which contains two electroclinic effect-based ferroelectric liquid crystal cells the rotation of the optic axes of each of said cells being continuously variable from about 1°

to about 11.25°

.

16. The multistable gray-scale light valve of claim 13 which contains three SSFLC cells.

17. The multistable gray-scale light valve of claim 13 which contains four SSFLC cells.

18. The multistable gray-scale light valve of claim 13 in which said cells are electroclinic-effect based cells.

19. The multiple gray-scale light valve of claim 18 wherein said electroclinic-effect based cells contain smectic A liquid crystal materials.