Tunable color filter

• US 5,689,317 A
• Filed: 03/22/1995
• Issued: 11/18/1997
• Est. Priority Date: 03/22/1995
• Status: Expired due to Fees

• Current Assignee: Cambridge Research & Instrumentation Incorporated (Revvity, Inc.)
• Original Assignee: Cambridge Research & Instrumentation Incorporated (Revvity, Inc.)
• Inventors: Miller, Peter
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MILLER, CHARLES LELAND
• Application Number:
  US08/408,378
• Time in Patent Office: 972 Days
• Field of Search: 359/63, 359/64, 359/53, 359/96, 349/97, 349/80, 349/112, 349/117
• US Class Current: 349/97
• 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

Abstract

A color filter having an optical switch element located between a neutral linear polarizer and a second color-selective linear polarizer, followed by one or more optical retarders and a second neutral linear polarizer. When a second optical switch element is incorporated, three color states are produced. The filter may also comprise a guest host type cell as the optical switch element. The resulting color filter exhibits high performance both for on-axis and off-axis rays and can be designed to produce a wide range of colors.

Claims

1. A tunable filter system for filtering light, comprising in optical alignment:

(a) a first neutral linear polarizer;

(b) an optical switch;

(c) a color-selective polarizer;

(d) an optical retarder; and

(e) a second neutral linear polarizer, said elements being arranged in a series order selected from a group of orders consisting of (a) through (e) and (e) through (a).

2. A tunable filter system in accordance with claim 1, wherein said optical switch is a liquid crystal cell.

3. A tunable filter system in accordance with claim 2, wherein said liquid crystal cell is a nematic variable retarder type cell.

4. A tunable filter system in accordance with claim 3, wherein said light being filtered has a wavelength of λ

and wherein said liquid crystal cell exhibits a retardance selected from a group of retardances consisting of substantially 0 and λ

/2 for said light being filtered.

5. A tunable filter system in accordance with claim 1, wherein said first neutral linear polarizer has a first linear polarizer axis, and wherein said optical switch has at least one selectable crystal axis orientation substantially 45°

to said first linear polarizer axis.

6. A tunable filter system in accordance with claim 1, wherein said first neutral linear polarizer has a first linear polarizer axis, and wherein said optical switch has at least one selectable crystal axis orientation substantially parallel to said first linear polarizer axis.

7. A tunable filter system in accordance with claim 1, wherein said first neutral linear polarizer has a first linear polarizer axis, and wherein said optical switch has at least one selectable crystal axis orientation substantially perpendicular to said first linear polarizer axis.

8. A tunable filter system in accordance with claim 1, wherein said first neutral linear polarizer has a first linear polarizer axis, and wherein said optical switch is switchable among a plurality of selectable crystal axis orientations selected from a group of orientations consisting of substantially 45°

to said first linear polar axis, substantially parallel to said first linear polarizer axis and substantially perpendicular to said first linear polarizer axis.

9. A tunable filter system in accordance with claim 1, wherein said first neutral linear polarizer has a first polarizer axis, and wherein said optical switch has a first crystal axis orientation which is substantially 221/2°

to said first polarizer axis and a second crystal axis orientation which is substantially 671/2°

to said first polarizer axis.

10. A tunable filter system in accordance with claim 1, wherein said first neutral linear polarizer has a first polarizer axis, and wherein said optical switch has a first orientation which is substantially 221/2°

to said first crystal axis polarizer axis in a first rotational sense and a second crystal axis orientation which is substantially 221/2°

to said first polarizer axis in a second rotational sense.

11. A tunable filter system in accordance with claim 1, wherein said optical switch is a surface stabilized ferroelectric liquid crystal (SSFLC) type cell.

12. A tunable filter system in accordance with claim 11, wherein said light being filtered has a range of wavelengths centered about a wavelength of λ

and wherein said SSFLC cell has a retardance of substantially λ

/2.

13. A tunable filter system in accordance with claim 1, wherein said color-selective polarizer exhibits high transmission for wavelengths of light having a first polarization state, and wherein said color-selective polarizer absorbs light of preselected wavelengths having a second polarization state.

14. A tunable filter system in accordance with claim 13, wherein said second polarization state is orthogonal to said first polarization state.

15. A tunable filter system in accordance with claim 1, wherein said color-selective polarizer absorbs a preselected range of wavelengths of light having a first polarization state, and wherein said color-selective polarizer absorbs a different preselected range of wavelengths of light having a second polarization state.

16. A tunable filter system in accordance with claim 15, wherein said second polarization state is orthogonal to said first polarization state.

17. A tunable filter system in accordance with claim 1, wherein said filter system has an overall retardance value and further comprises a second optical switch positioned adjacent said optical retarder element for varying said overall retardance value.

18. A tunable filter system in accordance with claim 17, wherein said second optical switch is a liquid crystal cell.

19. A tunable filter system in accordance with claim 18, wherein said optical retarder element has a retarder crystal axis and wherein said liquid crystal cell is a nematic variable retarder type cell having a liquid crystal cell axis orientation selected from a group of orientations consisting of substantially parallel to said retarder crystal axis and substantially perpendicular to said retarder crystal axis.

20. A tunable filter system in accordance with claim 18, wherein said optical retarder element has a retarder crystal axis and wherein said liquid crystal cell is a surface-stabilized ferroelectric liquid crystal (SSFLC) type cell having a first selectable SSFLC axis orientation at substantially 45°

to said fixed retarder crystal axis and a second selectable SSFLC axis orientation selected from a group of orientations consisting of substantially parallel to said fixed retarder crystal axis and substantially perpendicular to said fixed retarder crystal axis.

21. A tunable filter system in accordance with claim 1, wherein said optical switch is selected from a group consisting of a twisted nematic liquid crystal cell and a supertwist twisted nematic liquid crystal cell.

22. A tunable filter system in accordance with claim 1, wherein said light to be filtered has a spectrum, and wherein said spectrum is selected from a group consisting of visible light, near-infrared light, infrared light and ultraviolet light.

23. A tunable filter system in accordance with claim 1, wherein said optical retarder has a crystal axis oriented at substantially 45 degrees relative to said first neutral linear polarizer.

24. A tunable filter system for filtering light, comprising in optical alignment:

(a) a first neutral linear polarizer;

(b) an optical switch containing a color selective dye for selectively passing a preselected wavelength of light;

(c) an optical retarder element having a crystal axis oriented at substantially 45 degrees relative to said first neutral linear polarizer; and

(d) a second neutral linear polarizer, said elements being arranged in a series order selected from a group of orders consisting of (a) through (d) and (d) through.

25. A tunable filter in accordance with claim 24, wherein said optical switch is a first liquid crystal cell.

26. A tunable filter in accordance with claim 24, wherein said optical switch is a first liquid crystal cell selected from a group consisting of a twisted nematic guest host liquid crystal cell and a supertwist twisted nematic guest host liquid crystal cell.

27. A tunable filter system in accordance with claim 26, wherein said first liquid crystal cell is a twisted nematic guest host liquid crystal cell and said second optical switch is a second liquid crystal cell.

28. A tunable filter system in accordance with claim 27, wherein said optical retarder element has a retarder crystal axis and wherein said second liquid crystal cell is a nematic variable retarder type cell having a liquid crystal cell axis orientation selected from a group of orientations consisting of Substantially parallel to said retarder crystal axis and substantially perpendicular to said retarder crystal axis.

29. A tunable filter system in accordance with claim 27, wherein said optical retarder element has a retarder crystal axis and wherein said second liquid crystal cell is a surface-stabilized ferroelectric liquid crystal (SSFLC) type cell having a first selectable SSFLC axis orientation at substantially 45°

to said fixed retarder crystal axis and a second selectable SSFLC axis orientation selected from a group of orientations consisting of substantially parallel to said fixed retarder crystal axis and substantially perpendicular to said fixed retarder crystal axis.

30. A tunable filter system in accordance with claim 24, wherein said filter system has an overall retardance value and further comprises a second optical switch positioned adjacent said optical retarder element for varying said overall retardance value.

31. A tunable filter system in accordance with claim 24, wherein said light to be filtered has a spectrum, and wherein said spectrum is selected from a group consisting of visible light, near-infrared light, infrared light and ultraviolet light.

32. A tunable color filter system for filtering light, comprising in optical alignment:

(a) a first neutral linear polarizer having a preselected polarization axis;

(b) an optical switch capable of selectably transmitting light in a first substantially linear polarization state and a second substantially linear polarization state, said second polarization state being substantially orthogonal to said first polarization state;

(c) a color-selective polarizer having an axis substantially parallel to a polarization state selected from a group consisting of said first polarization state and said second polarization state;

(d) an optical retarder having a retarder crystal axis substantially at an angle selected from a first group of angles consisting of substantially 45°

greater than said first polarization state and substantially 45°

less than said first polarization state; and

(e) a second neutral linear polarizer having a polarization axis substantially at an angle selected from a second group of angles consisting of substantially parallel to said first polarization state and substantially parallel to said second polarization state, said elements being arranged in a series order selected from a group of orders consisting of (a) through (e) and (e) through (a).

33. A tunable filter system in accordance with claim 32, wherein said optical switch is a twisted nematic liquid crystal cell.

34. A tunable filter system in accordance with claim 32, wherein said optical switch is a surface stabilized ferroelectric liquid crystal (SSFLC) type cell.

35. A tunable filter system in accordance with claim 34, wherein said light being filtered has a wavelength of λ

and wherein the SSFLC cell retardance is substantially λ

/2 for the light being filtered.

36. A tunable filter system in accordance with claim 32, wherein said optical switch is a liquid crystal cell.

37. A tunable filter system in accordance with claim 36, wherein said first neutral linear polarizer has a first linear polarizer axis, and wherein said liquid crystal cell has a crystal axis orientation switchable among a plurality of selectable crystal axis orientations, at least one of said plurality of selectable crystal axis orientations having an orientation selected from a group of orientations consisting of substantially 45°

to said first linear polarizer axis, substantially parallel to said first linear polarizer axis and substantially perpendicular to said first linear polarizer axis.

38. A tunable filter system in accordance with claim 36, wherein said first neutral linear polarizer has a first polarizer axis, and wherein said liquid crystal cell has a crystal axis having a first orientation which is substantially 221/2°

to said first polarizer axis and a second orientation which is substantially 671/2°

to said first polarizer axis.

39. A tunable filter system in accordance with claim 36, wherein said first neutral linear polarizer has a first polarizer axis, and wherein said liquid crystal cell has a crystal axis having a first orientation which is substantially 221/2°

to said first polarizer axis in a first rotational sense and a second orientation which is substantially 221/2°

to said first polarizer axis in a second rotational sense.

40. A tunable filter system in accordance with claim 36, wherein said filter system has an overall retardance value and further comprises a second liquid crystal cell positioned adjacent said optical retarder element for varying said overall retardance value.

41. A tunable filter system in accordance with claim 40, wherein said second liquid crystal cell is a variable-retardance nematic type cell having a liquid crystal cell axis orientation selected from a group of orientations consisting of substantially parallel to said retarder crystal axis and substantially perpendicular to said retarder crystal axis.

42. A tunable filter system in accordance with claim 40, wherein said second liquid crystal cell is a surface-stabilized ferroelectric liquid crystal (SSFLC) type cell having a first selectable SSFLC axis orientation at substantially 45°

to said retarder crystal axis and a second selectable SSFLC axis orientation selected from a group of orientations consisting of substantially parallel to said retarder crystal axis and substantially perpendicular to said retarder crystal axis.

43. A tunable filter system in accordance with claim 32, wherein said optical switch is a supertwist twisted nematic liquid crystal cell.

44. A tunable filter system in accordance with claim 32, where the liquid crystal cell is a nematic variable retarder type cell.

45. A tunable filter system in accordance with claim 44, wherein said light being filtered has a wavelength of λ

and wherein said nematic variable retarder type cell exhibits retardances of substantially 0 and λ

/2 for the light being filtered.

46. A tunable filter system in accordance with claim 32, wherein said color-selective polarizer exhibits high transmission for wavelengths of light having a first polarization state, and wherein said color-selective polarizer absorbs light of preselected wavelengths having a second polarization state which is orthogonal to said first polarization state.

47. A tunable filter system in accordance with claim 32, wherein said light to be filtered has a spectrum, and wherein said spectrum is selected from a group of spectrums consisting of visible light, near-infrared light, infrared light and ultraviolet light.

48. A tunable filter system in accordance with claim 32, wherein said color-selective polarizer absorbs a preselected range of wavelengths of light having a first polarization state, and wherein said color-selective polarizer absorbs a different preselected range of wavelengths of light having a second polarization state which is orthogonal to said first polarization state.

49. A tunable filter system for filtering light, comprising in optical alignment:

(a) a first neutral linear polarizer having a first preselected polarization axis;

(b) a twisted nematic guest host liquid crystal cell containing a color-selective dye and having a liquid crystal axis substantially parallel to said first preselected polarization axis;

(c) an optical retarder having a retarder crystal axis substantially 45°

to said first preselected polarization axis; and

(d) a second neutral linear polarizer having a second preselected polarization axis, said second preselected polarization axis having an orientation selected from a group consisting of substantially parallel to said first preselected polarization axis and substantially perpendicular to said first preselected polarization axis, said elements being arranged in a series order selected from a group of orders consisting of (a) through (d) and (d) through (a).

50. A tunable filter system in accordance with claim 49, wherein said filter system has an overall retardance value and further comprises a second liquid crystal cell positioned adjacent said fixed retarder for varying said overall retardance value.

51. A tunable filter system in accordance with claim 50, wherein said second liquid crystal cell is a surface-stabilized ferroelectric liquid crystal (SSFLC) cell having an SSFLC crystal axis, said SSFLC crystal axis having an orientation selected from a group consisting of substantially 45°

to said fixed retarder crystal axis, substantially parallel to said fixed retarder crystal axis and substantially perpendicular to or said fixed retarder crystal axis.

52. A tunable filter system in accordance with claim 50, wherein said light to be filtered has a spectrum, and wherein said spectrum is selected from a group of spectrums consisting of visible light, near-infrared light, infrared light and ultraviolet light.

53. A tunable filter system in accordance with claim 50, wherein said second liquid crystal cell is a nematic variable retarder type cell having a second liquid crystal axis, said second liquid crystal axis having an orientation selected from a group consisting of substantially parallel to said retarder crystal axis and substantially perpendicular to said retarder crystal axis.

54. A tunable filter system in accordance with claim 49, wherein said twisted nematic guest host liquid crystal cell is a supertwist twisted nematic guest host liquid crystal cell.