Chiral smectic liquid crystal optical modulators

• US 5,552,912 A
• Filed: 05/13/1994
• Issued: 09/03/1996
• Est. Priority Date: 11/14/1991
• Status: Expired due to Fees

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Sharp, Gary D., Johnson, Kristina M.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): TRICE, RONALD
• Application Number:
  US08/244,017
• Time in Patent Office: 844 Days
• Field of Search: 359/56, 359/71, 359/72, 359/73, 359/87, 359/100, 359/260, 359/77
• US Class Current: 349/117
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/133738 for homogeneous alignment
• CPC Class Codes: G02F 1/133742 for homeotropic alignment
• CPC Class Codes: G02F 1/134309 characterised by their geometrical arrangement
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]
• CPC Class Codes: G02F 1/13439 characterised by their electrical, optical, physical properties; materials therefor; method of making
• CPC Class Codes: G02F 1/13471 in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells G02F1/13475 takes precedence
• 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
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals
• CPC Class Codes: G02F 1/1418 using smectic liquid crystals, e.g. based on the electroclinic effect
• CPC Class Codes: G02F 1/216 using liquid crystals, e.g. liquid crystal Fabry-Perot filters
• CPC Class Codes: G02F 2203/05 wavelength dependent
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/06 Polarisation independent
• CPC Class Codes: G02F 2203/50 Phase-only modulation

Abstract

The present invention provides optical modulators which comprise aligned chiral smectic liquid crystal cells within an optical resonance cavity. The cavity configurations include symmetric and asymmetric Fabry-Perot etalons. The liquid crystal cells can be planar- or homeotropically-aligned and can be discrete state or analog cells. The device configurations of the present invention provide discrete or continuous optical modulation of the phase, intensity, and wavelength of elliptically polarized light, without requiring polarization analyzers. The modulators are optically or electronically addressable in single pixels or arrays of multiple pixels. Certain homeotropically-aligned cells are provided as an aspect of this invention, as are certain variable retarders comprised of planar-aligned cells in combination with birefringent elements.

Claims

1. A multiple element etalon modulator for light comprising:

a multiple element intracavity modulator, which comprises;

a smectic liquid crystal cell, the optic axis of which is rotatable by application of an electric field parallel to the smectic layers of said cell;

means for applying an electric field to said smectic liquid crystal cell whereby said optic axis of said liquid crystal cell is rotated; and

a birefringent element; and

a front and a back reflective surface positioned on either side of said multiple element intracavity modulator to form an etalon.

2. The multiple element etalon modulator of claim 1 wherein said liquid crystal cell is selected from the group consisting of a planar aligned SmA* cell, a planar aligned SmC* cell, a planar aligned DHF cell, a homeotropically aligned SmA* cell, a homeotropically aligned SmC* cell and a homeotropically aligned DHF cell.

3. The multiple element etalon modulator of claim 1 wherein said birefringent element is a passive birefringent element.

4. The multiple element etalon modulator of claim 1 wherein said birefringent element comprises a second smectic liquid crystal cell, the optic axis of which is rotatable by application of an electric field parallel to the smectic layers of said second cell, whereby said multiple element modulator comprises two liquid crystal cells.

5. The multiple element etalon modulator of claim 4 wherein said two liquid crystal cells are selected from the group consisting of:

two planar-aligned, surface-stabilized SmA* liquid crystal cells in series within the optical cavity, the optic axes of which cells are configured to rotate in opposite directions;

two planar-aligned DHF liquid crystal cells in series within the optical cavity, the optic axes of which cells are configured to rotate in the same direction;

two planar-aligned DHF liquid crystal cells in series within the optical cavity, the optic axes of which cells are configured to rotate in opposite directions; and

a planar-aligned DHF liquid crystal cell and a planar-aligned, surface-stabilized SmA* liquid crystal cell in series within the optical cavity, the optic axes of which cells are configured to rotate in the same direction.

6. A modulator which comprises a homeotropically aligned smectic liquid crystal cell, wherein the molecular director of said liquid crystal is rotatable in an analog fashion by application of an electric field parallel to the smectic layers of said cell, and lateral electrodes for applying an electric field to said liquid crystal cell parallel to the smectic liquid crystal layers of said cell.

7. The modulator of claim 6 wherein said liquid crystal cell is a distorted helix ferroelectric cell.

8. A multi-pixel array wherein each pixel is a modulator of claim 6.

9. The multi-pixel array of claim 8 wherein each pixel of said array is individually addressable.

10. The multi-pixel array of claim 8 further including photosensor means electrically connected to said modulators whereby said array is optically addressable.