Chiral smectic liquid crystal polarization interference filters

• US 5,243,455 A
• Filed: 05/15/1992
• Issued: 09/07/1993
• Est. Priority Date: 05/11/1990
• Status: Expired due to Term

• Current Assignee: RealD Incorporated
• Original Assignee: University of Colorado System
• Inventors: Sharp, Gary D., Johnson, Kristina M.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/884,644
• Time in Patent Office: 480 Days
• Field of Search: 359/53, 359/56, 359/73, 359/93, 359/94, 359/100
• US Class Current: 349/18
• 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 1/216 using liquid crystals, e.g. liquid crystal Fabry-Perot filters
• CPC Class Codes: G02F 2203/055 wavelength filtering

Abstract

Discretely and continuously tunable single and multiple-stage polarization interference filters employing chiral smectic liquid crystal cells as electronically rotatable retarders are provided. Discretely tunable filters of this invention include those which employ bistable surface-stabilized ferroelectric liquid crystal cells. Continuously tunable filters of this invention include those that employ chiral smectic A ferroelectric liquid crystal cells. Single stage filters include fixed birefringent elements in combination with chiral smectic liquid crystal cells and multiple stage filters can include only chiral smectic liquid crystal cells or can include chiral smectic liquid crystal cells in combination with fixed birefringent elements. Blocking filters useful for color generation and color displays are also provided. The FLC filters provided can be temporally multiplexed.

Claims

1. A tunable optical filter comprising one or more stages optically coupled in sequence wherein a stage comprises an entrance polarizer which defines the polarization of light entering the stage and an exit polarizer which is oriented at a fixed angle with respect to the entrance polarizer, wherein at least one stage of said filter comprises a fixed birefringent element optically coupled with a chiral smectic liquid crystal cell between said polarizers, said chiral smectic liquid crystal cell having two or more optic axis orientations, and electric field production means electromagnetically coupled with said chiral smectic liquid crystal cell for rotating the optic axis of said cell among said optic axis orientations to tune the spectral filtering of said light entering the stage.

2. The tunable optical filter of claim 1 wherein said filter comprises two or more stages.

3. The tunable optical filter of claim 1 wherein each of said stages comprises a fixed birefringent element.

4. The tunable optical filter of claim 1 wherein each of said stages comprises at least one chiral smectic ferroelectric liquid crystal cell.

5. The tunable optical filter of claim 1 wherein said chiral smectic liquid crystal cell has exactly two stable optic axis orientations.

6. The tunable optical filter of claim 5 wherein said chiral smectic liquid crystal cell is a bistable SSFLC cell.

7. The tunable optical filter of claim 1 wherein said entrance and exit polarizers are oriented at 0°

or 90°

with respect to one another.

8. The tunable optical filter of claim 1 wherein said fixed birefringent element within a stage is oriented at an angle of ±

45°

with respect to the direction of polarization of light entering that stage.

9. The tunable optical filter of claim 1 wherein at least one stage comprises two or more chiral smectic liquid crystal cells.

10. The tunable optical filter of claim 1 wherein said chiral smectic liquid crystal cell is a ferroelectric liquid crystal cell.

11. The tunable optical filter of claim 1 which contains two or more chiral smectic liquid crystal cells and wherein said optic axes of said cells are independently rotatable among said optic axis orientations.

12. The tunable optical filter of claim 1 which contains two or more chiral smectic liquid crystal cells and wherein said optic axes of said cells are synchronously rotatable among said optic axis orientations.

13. The tunable optical filter of claim 1 wherein the chiral smectic liquid crystal cell within a stage is oriented such that one of the optic axis orientations of the cell is at 0°

, ±

45°

or 90°

with respect to the polarization of light entering that stage.

14. The tunable optical filter of claim 1 wherein in said chiral smectic liquid crystal cell two of said optic axis orientations of said cell are separated from each other by an angle of ±

45°

.

15. The tunable optical filter of claim 1 wherein said chiral smectic liquid crystal cell is an analog chiral smectic liquid crystal cell the optic axis of which can be continuously rotated between ±

α

_MAX of the cell.

16. The tunable optical filter of claim 15 wherein said analog chiral smectic liquid crystal cell is a chiral smectic A electroclinic cell or a distorted helix ferroelectric cell.

17. The tunable filter of claim 1 which comprises two or more stages and wherein the ratios of thicknesses of any of the chiral smectic liquid crystal cells and fixed birefringent elements to the thicknesses of any other chiral smectic liquid crystal cell or birefringent element within a stage are the same in all stages of the filter.

18. The tunable filter of claim 2 which has a Lyot-type geometry wherein the thicknesses of the chiral smectic liquid crystal cells and birefringent elements in the stages of said filter increase in a geometric progression:

2⁰, 2¹, 2², . . . , 2^S-1 where S is the number of stages in the filter wherein the thicknesses of the cells and elements in a stage do not necessarily increase in the order of stages in the filter.

19. The tunable filter of claim 1 which is operated in reflective mode.

20. A tunable optical filter comprising one or more optically coupled stages along a light propagation axis wherein a stage comprises an entrance polarizer and an exit polarizer which are oriented at a fixed angle with respect to each other, wherein the entrance polarizer of a stage defines the polarization of light entering that stage wherein one or more stages of said filter comprise N chiral smectic liquid crystal cells positioned between said polarizers and optically coupled with said polarizers said chiral smectic liquid crystal cell having two or more optical axis orientations and means for applying an electric field to said chiral smectic liquid crystal cell whereby said optic axis of said cell is rotated among said optical axis orientations wherein, when the filter has one stage, N is three or more, and when the filter has more than one stage, N is one or more.

21. The tunable optical filter of claim 20 wherein at least one of said stages comprises a fixed birefringent element.

22. The tunable optical filter of claim 21 wherein each of said stages comprises a fixed birefringent element.

23. A continuously tunable optical filter having one or more optically coupled stages wherein a stage comprises:

an entrance polarizer which defines the polarization of light entering the stage and an exit polarizer which is oriented at a fixed angle with respect to the polarization of light entering the stage, a birefringent element which can be active or fixed, an achromatic quarter-waveplate and an analog chiral smectic liquid crystal cell all of which are optically coupled between said polarizers wherein said achromatic quarter-waveplate is optically coupled between said birefringent element and said analog chiral smectic liquid crystal cell and means for applying a variable electric field to said analog chiral smectic liquid crystal cell such that the optic axis of said cell be rotated with the magnitude of said rotation being dependent on the sign and magnitude of said applied field and α

_MAX of said analog chiral smectic cell.

24. The tunable optical filter of claim 23 wherein said filter comprises two or more stages.

25. The tunable optical filter of claim 23 wherein said birefringent element is a fixed birefringent element.

26. The tunable optical filter of claim 25 wherein said fixed birefringent element in a stage is oriented at an angle of ±

45°

with respect to the direction of polarization of light entering that stage.

27. The tunable optical filter of claim 23 wherein said birefringent element is an active birefringent element.

28. The tunable optical filter of claim 27 wherein said active birefringent element is a chiral smectic liquid crystal cell.

29. The tunable optical filter of claim 28 wherein said chiral smectic liquid crystal cell is a chiral smectic C bistable SSFLC cell.

30. The tunable optical filter of claim 23 wherein said entrance and exit polarizers are oriented parallel or perpendicular with respect to one another.

31. The tunable optical filter of claim 23 wherein said analog chiral smectic liquid crystal cell cell is an electroclinic or DHF cell.

32. The tunable optical filter of claim 23 wherein said analog chiral smectic liquid crystal cell displays a maximum tilt angle of ±

22.5 °

.

33. The tunable optical filter of claim 23 wherein said achromatic quarter-waveplate within a stage is oriented at 0 or 90°

with respect to the polarization of light entering said stage.