High performance switchable polarizers for optical projection displays and circuits for driving the polarizers

• US 7,339,563 B1
• Filed: 02/01/2000
• Issued: 03/04/2008
• Est. Priority Date: 02/01/2000
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Goyins, Gregg S., Lawton, Robert J.
• Primary Examiner(s): Hjerpe; Richard
• Assistant Examiner(s): Nguyen; Kevin M
• Application Number:
  US09/497,021
• Time in Patent Office: 2,954 Days
• Field of Search: 345/87, 345/32, 345/101, 345/102, 345/88, 345/38, 345/40, 345/204, 349/16, 349/18, 349/119, 349/78, 349/97, 349/196, 349/193, 349/197, 349/20, 349/21, 349/72, 349/161, 359/498, 359/499, 9 19- 55, 9 7/8, 9 8/0, 9 8/2, 9 9/7
• US Class Current: 345/87
• CPC Class Codes: G02F 1/132 Thermal activation of liquid crystals exhibiting a thermo-optic effect
• CPC Class Codes: G02F 2203/07 Polarisation dependent
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

The invention is directed towards high performance switchable polarizers for optical projection displays. One embodiment of the invention is a switchable polarizer with (1) two conductive electrodes and (2) a liquid crystal material that is positioned between the two conductive electrodes. The electrodes apply a uniform electric field across the liquid crystal material when one of the electrodes is placed at a first potential and other electrode is placed at a second potential different from the first potential. These two electrodes also heat the liquid crystal material when they conduct current. When equal currents are drawn through the electrodes, the electrodes apply a uniform electric field across the liquid crystal during a heating operation.

Claims

1. A switchable polarizer for optical projection displays, said switchable polarizer comprising:

a first electrode having a first set of contacts;

a second electrode having a second set of contacts; and

a layer of liquid crystal material positioned between the first and second electrodes;

wherein the first electrode conducts current between said first set of contacts to heat the polarizer, and wherein the second electrode conducts current between said second set of contacts to heat the polarizer.

2. The switchable polarizer of claim 1, wherein the current passing through the first electrode is equal in magnitude to the current passing through the second electrode.

3. The switchable polarizer of claim 2, wherein the currents passing through the first and second electrodes are constant.

4. The switchable polarizer of claim 2, wherein during a heating operation, the first and second electrodes apply a uniform electric field across the liquid crystal material.

5. The switchable polarizer of claim 1, wherein no current passes through the first and second electrodes when the electrodes are not heating the polarizer.

6. The switchable polarizer of claim 1, wherein during a non-heating operation of the polarizer, no current passes through either electrode, and the first electrode is at a first potential and the second electrode is at a second potential different from the first potential.

7. The switchable polarizer of claim 1, wherein the first and second electrodes are transparent electrodes.

8. The switchable polarizer of claim 1, wherein the first electrode receives a first voltage signal and the second electrode receives a second voltage signal.

9. The switchable polarizer of claim 8, wherein the first and second voltage signals are alternating signals.

10. The switchable polarizer of claim 9, wherein the first and second voltage signals are symmetrically opposite bipolar signals.

11. The switchable polarizer of claim 1, wherein the polarizer serves as a polarization compensator in an optical projection display.

12. The switchable polarizer of claim 1, wherein the polarizer is a polarizing switch of an electronic color switch.

13. A method of driving a switchable polarizer in one of two modes, the switchable polarizer having first and second electrodes and a liquid crystal material between the electrodes, wherein during a first driving mode, the electrodes heat the liquid crystal material, while during the second driving mode, the electrodes do not heat the liquid crystal material, said method comprising:

drawing equal currents through the first and second electrodes during the first driving mode, wherein the drawing of currents through the electrodes includes coupling the electrodes to two current sources; and

applying a first voltage signal to the first electrode and a second voltage signal to the second electrode during both the first and second driving modes, the first and second voltage signals sustaining the currents drawn through the first and second electrodes during the first driving mode, wherein the applying of the voltage signals to the electrodes includes coupling each electrode to an output of an amplifier.

14. The method of claim 13, wherein the applying of the voltage signals to the electrodes includes applying first and second voltage signals that are alternating signals.