Chromaticity compensating liquid crystal filter

• US 6,172,722 B1
• Filed: 01/22/1999
• Issued: 01/09/2001
• Est. Priority Date: 11/25/1996
• Status: Expired due to Term

• Current Assignee: RealD Incorporated
• Original Assignee: ColorLink, Incorporated (RealD Incorporated)
• Inventors: Sharp, Gary D.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGO, HUYEN LE
• Application Number:
  US09/235,638
• Time in Patent Office: 718 Days
• Field of Search: 349/80, 349/97, 349/106, 349/120, 349/119, 348/742, 348/744, 359/483, 359/485, 359/494, 359/498, 359/499, 359/502, 359/634
• US Class Current: 349/80
• CPC Class Codes: G02F 1/133533 Colour selective polarisers G02F1/1347 takes precedence
• CPC Class Codes: G02F 1/13473 for wavelength filtering or for colour display without the use of colour mosaic filters
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence

Abstract

This invention provides chromaticity compensation for color filters having nematic liquid crystal tuning elements, as well as fast-transition tuning units for use in combination with chromaticity compensation. The filters of this invention have two stages formed by three linear polarizers in series, as least two of which are color polarizers. Within each stage is a tuning unit comprising a nematic liquid crystal cell switchable between a first state wherein the polarization of light is orthogonally transformed and a second state wherein the polarization is unchanged. In the first state the liquid crystal cell chromaticity introduces significant distortion to the filter stage, but in the second state it does not. Chromaticity compensation is achieved in this invention by optimizing the use of the undistorted normal states and by judicious choice of the design wavelengths of the liquid crystal cells. This invention further provides compound tuning units, for use in the chromaticity compensating filter, that allow the use of fast unenergized-to-energized transitions in switching between three primary colors. A first embodiment of the compound tuning unit uses a half-wave bias retarder oriented at ±45° in combination with the nematic liquid crystal cell. A second embodiment of the compound tuning unit uses two nematic liquid crystal cells. A third embodiment of the compound tuning unit uses a half-wave bias retarder oriented at about ±67° or ±23° in combination with the nematic liquid crystal cell.

Claims

1. A chromaticity compensating filter, comprising:

a first stage, comprising;

a first and a second linear polarizer, at least one of the first and second polarizers being a color polarizer; and

a first tuning unit positioned between the first and second polarizers and switchable between a first state wherein the polarization of light is orthogonally transformed and a second state wherein the polarization is unchanged; and

a second stage in series with the first stage, comprising;

the second linear polarizer and a third linear polarizer, at least two of the first, second and third polarizers being color polarizers; and

a second tuning unit positioned between the second and third polarizers and switchable between a first state wherein the polarization of light is orthogonally transformed and a second state wherein the polarization is unchanged,

wherein the first stage normally transmits a first subtractive primary color and the second stage normally transmits a second subtractive primary color.

2. The chromaticity compensating filter of claim 1, wherein the first and second subtractive primary colors overlap in an additive primary color.

3. The chromaticity compensating filter of claim 2, wherein a design wavelength of at least one of the first and second tuning units falls within a region of the overlap.

4. The chromaticity compensating filter of claim 2, wherein the first and second tuning units, when in their respective first states, optimize blocking of the additive primary color in which the first and second subtractive primary color overlap.

5. The chromaticity compensating filter of claim 1, wherein one of the first and second tuning units is a liquid crystal cell.

6. The chromaticity compensating filter of claim 5, wherein the one of the first and second tuning units is one of an electrically controlled birefringence nematic cell, a twisted nematic cell, a super twisted nematic cell, a zero-twist nematic cell, and a π

-cell.

7. The chromaticity compensating filter of claim 5, wherein the first tuning unit has a retardance switchable between half-wave and zero.

8. The chromaticity compensating filter of claim 7, wherein the first tuning unit has its optical axis oriented at 45°

relative to at least one of a polarization of the first polarizer and a polarization of the second polarizer.

9. The chromaticity compensating filter of claim 1, wherein the color polarizers are polarizer-retarder-stacks, each polarizer-retarder-stack comprising:

a neutral linear polarizer; and

a retarder stack comprising two or more retarders, wherein the number, N, of the retarders and the retardances and orientations of the retarders are such that a first additive primary color spectrum is transmitted along a first polarization axis and the complementary first subtractive primary color spectrum is transmitted along a second, orthogonal, polarization axis.

10. The chromaticity compensating filter of claim 1, wherein one of the first subtractive primary color and the second subtractive primary color is yellow and the other of the first subtractive primary color and the second subtractive primary color is cyan.

11. The chromaticity compensating filter of claim 1, wherein one of the first subtractive primary color and the second subtractive primary color is yellow and the other of the first subtractive primary color and the second subtractive primary color is magenta.

12. The chromaticity compensating filter of claim 1, wherein one of the first subtractive primary color and the second subtractive primary color is magenta and the other of the first subtractive primary color and the second subtractive primary color is cyan.

13. The chromaticity compensating filter of claim 1, wherein each of the color polarizers is one of a dye-type pleochroic color polarizer and a polarizer-retarder stack.

14. The chromaticity compensating filter of claim 1, wherein the first tuning unit comprises two liquid crystal cells, each switchable between a first state wherein the polarization of light is orthogonally transformed and a second state wherein the polarization is unchanged.

15. A display comprising the chromaticity compensating filter of claim 1.

16. A camera comprising:

the chromaticity compensating filter of claim 1; and

a receiver array in series with the filter.

17. A method of filtering electromagnetic radiation, comprising:

radiating the electromagnetic radiation on the chromaticity compensating filter of claim 1; and

sequentially switching the first and second tuning units through their respective first and second states, resulting in a plurality of filter transmission states.

18. The method of claim 17, wherein the plurality of filter transmission states correspond to red, green and blue transmission spectra.

19. The method of claim 18, wherein the sequential switching utilizes only unenergized to energized transitions of the first and second tuning units.

20. The method of claim 19, wherein one of the first and second tuning units further comprises a half-wave bias retarder.