Cholesteric liquid crystal display employing circular polarizer and methods of operation and manufacture therefor

• US 5,796,454 A
• Filed: 12/04/1996
• Issued: 08/18/1998
• Est. Priority Date: 12/04/1996
• Status: Expired due to Term

• Current Assignee: Kent Display Systems Incorporated
• Original Assignee: Advanced Display Systems Incorporated
• Inventors: Ma, Yao-Dong
• Primary Examiner(s): GROSS, ANITA P
• Application Number:
  US08/767,111
• Time in Patent Office: 622 Days
• Field of Search: 349/98, 349/176, 349/175
• US Class Current: 349/98
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/1347 Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 2203/09 transflective

Abstract

A cholesteric liquid crystal display ("LCD") and methods of operating and manufacturing the LCD. The LCD includes: (1) a controllable cholesteric liquid crystal (CLC) located between first and second substrates, the controllable CLC selectively exhibiting an "on" state and an "off" state and having a circular polarity of a predetermined handedness when the controllable CLC is in the "on" state and (2) a circular polarizer, located proximate the first substrate and having a circular polarity of a particular handedness, that cooperates with the controllable CLC to increase the difference between the relative brightness of the "on" state and the "off" state, whereby a contrast ratio of the cholesteric LCD is increased.

Claims

1. A cholesteric liquid crystal display (LCD), comprising:

a controllable cholesteric liquid crystal (CLC) located between first and second substrates, said controllable CLC selectively exhibiting an "on" state and an "off" state and having a circular polarity of a predetermined handedness when said controllable CLC is in said "on" state; and

a circular polarizer, located proximate said first substrate and having a circular polarity of a particular handedness, that cooperates with said controllable CLC to increase the difference between the relative brightness of said "on" state and said "off" state, whereby a contrast ratio of said cholesteric LCD is increased.

2. The LCD as recited in claim 1 wherein said circular polarizer attenuates a substantial portion of light reflected from said first substrate.

3. The LCD as recited in claim 1 further comprising:

a second circular polarizer, located proximate said second substrate and having an arbitrary handedness; and

a reflector located on an opposite side of said second circular polarizer from said second substrate, said second circular polarizer and said reflector cooperating to absorb light transmitted through said controllable CLC.

4. The LCD as recited in claim 1 wherein said predetermined handedness equals said particular handedness, said controllable CLC reflecting wavelengths of light corresponding to an intrinsic color of said controllable CLC and transmitting all other wavelengths of light when said controllable CLC is in said "on" state, said LCD thereby adapted to cooperate with a projector to project said all other wavelengths of light when said controllable CLC is in said "on" state, said LCD scattering all wavelengths of light when said controllable CLC is in said "off" state.

5. The LCD as recited in claim 1 wherein said predetermined handedness is opposite said particular handedness, said LCD thereby adapted to cooperate with a projector to project white light when said controllable CLC is in said "on" state, said LCD scattering said light when said controllable CLC is in said "off" state.

6. The LCD as recited in claim 5 further comprising a color filter proximate said controllable CLC, said color filter causing said LCD to cooperate with said projector to project a colored light when said controllable CLC is in said "on" state, said LCD scattering said colored light when said controllable CLC is in said "off" state.

7. The LCD as recited in claim 6 wherein said color filter is a multicolor filter, said multicolor filter causing said LCD to cooperate with said projector to project a multicolored light when said controllable CLC is in said "on" state, said LCD scattering said colored light when said controllable CLC is in said "off" state.

8. The LCD as recited in claim 1 further comprising a second circular polarizer located proximate said second substrate of said controllable CLC and having a handedness that is opposite said predetermined handedness and said particular handedness, said second circular polarizer thereby blocking light transmitted through said controllable CLC when said controllable CLC is in said "on" state.

9. The LCD as recited in claim 8 further comprising a color filter proximate said controllable CLC, said color filter causing said LCD to transmit a colored light when said controllable CLC is in said "off" state.

10. The LCD as recited in claim 9 wherein said color filter is a multicolor filter, said color filter causing said LCD to transmit a multicolored light when said controllable CLC is in said "off" state.

11. The LCD as recited in claim 1 further comprising a polymer dispersed LC (PDLC), located between third and fourth substrates and on an opposite side of said second substrate from said controllable CLC, that allows said LCD to operate:

in a reflective mode wherein said PDLC is placed in an opaque state, and

in a transmissive mode wherein said PDLC is placed in a transparent state and light passing through said PDLC and said controllable CLC passes through said circular polarizer.

12. The LCD as recited in claim 11 further comprising a color filter, located proximate said second substrate, that causes said light to be a certain color when said LCD operates in said transmissive mode.

13. The LCD as recited in claim 12 wherein said color filter is a multicolor filter, said light being multicolored when said LCD operates in said transmissive mode.

14. The LCD as recited in claim 1 wherein said controllable CLC contains a twist agent that determines an intrinsic color of said controllable CLC.

15. The LCD as recited in claim 1 further comprising a drive circuit that provides a drive signal to selectively drive said controllable CLC to said "on" and said "off" states.

16. The LCD as recited in claim 1 wherein said controllable CLC is arranged in pixels, each of said pixels independently controllable to achieve said "on" and said "off" states.

17. The LCD as recited in claim 1 wherein said first and second substrates contain a conductive matrix that provides a path for drive voltage to be conveyed to said controllable CLC.

18. The LCD as recited in claim 17 wherein said conductive matrix defines pixel locations of said controllable CLC.

19. The LCD as recited in claim 1 wherein said first and second substrates are substantially parallel.

20. The LCD as recited in claim 1 wherein said predetermined handedness is right-handed.

21. A method of operating a cholesteric liquid crystal display (LCD), comprising the steps of:

controlling a controllable cholesteric liquid crystal (CLC) located between first and second substrates, said controllable CLC selectively exhibiting an "on" state and an "off" state and having a circular polarity of a predetermined handedness when said controllable CLC is in said "on" state; and

circularly polarizing light passing through a circular polarizer and incident on said controllable CLC, said circular polarizer located proximate said first substrate and having a circular polarity of a particular handedness, said circular polarizer cooperating with said controllable CLC to increase the difference between the relative brightness of said "on" state and said "off" state, whereby a contrast ratio of said cholesteric LCD is increased.

22. The method as recited in claim 21 further comprising the step of attenuating a substantial portion of light reflected from said first substrate with said circular polarizer.

23. The method as recited in claim 21 further comprising the steps of:

passing said light through a second circular polarizer located on an opposite side of said second substrate from said controllable CLC and having an arbitrary handedness; and

reflecting said light from a reflector located on an opposite side of said second circular polarizer from said second substrate, said second circular polarizer and said reflector cooperating to absorb light transmitted through said controllable CLC.

24. The method as recited in claim 21 wherein said predetermined handedness equals said particular handedness, said controllable CLC reflecting wavelengths of light corresponding to an intrinsic color of said controllable CLC and transmitting all other wavelengths of light when said controllable CLC is in said "on" state, said LCD adapted to cooperate with a projector, said method comprising the steps of:

projecting light of said all other wavelengths when said controllable CLC is in said "on" state; and

scattering all wavelengths of light when said controllable CLC is in said "off" state.

25. The method as recited in claim 21 wherein said predetermined handedness is opposite said particular handedness, said LCD adapted to cooperate with a projector to project white light when said controllable CLC is in said "on" state, said method comprising the step of scattering said light with said LCD when said controllable CLC is in said "off" state.

26. The method as recited in claim 25 further comprising the step of passing said light through a color filter proximate said controllable CLC, said color filter causing said LCD to cooperate with said projector to project a colored light when said controllable CLC is in said "on" state, said LCD scattering said colored light when said controllable CLC is in said "off" state.

27. The method as recited in claim 26 wherein said color filter is a multicolor filter, said multicolor filter causing said LCD to cooperate with said projector to project a multicolored light when said controllable CLC is in said "on" state, said LCD scattering said colored light when said controllable CLC is in said "off" state.

28. The method as recited in claim 21 further comprising the step of providing a second circular polarizer located on an opposite side of said second substrate from said controllable CLC and having a handedness that is opposite said predetermined handedness and said particular handedness, said second circular polarizer thereby blocking light transmitted through said controllable CLC when said controllable CLC is in said "on" state.

29. The method as recited in claim 28 further comprising the step of passing said light through a color filter proximate said controllable CLC, said color filter causing said LCD to transmit a colored light when said controllable CLC is in said "off" state.

30. The method as recited in claim 29 wherein said color filter is a multicolor filter, said color filter causing said LCD to transmit a multicolored light when said controllable CLC is in said "off" state.

31. The method as recited in claim 21 further comprising the step of providing a polymer dispersed LC (PDLC) on an opposite side of said second substrate from said controllable CLC, said PDLC allowing said LCD to operate:

in a reflective mode wherein said PDLC is placed in an opaque state, and

in a transmissive mode wherein said PDLC is placed in a transparent state and light passing through said PDLC and said controllable CLC passes through said circular polarizer.

32. The method as recited in claim 31 further comprising the step of passing said light through a color filter, located proximate said second substrate, that causes said light to be a certain color when said LCD operates in said transmissive mode.

33. The method as recited in claim 32 wherein said color filter is a multicolor filter, said light being multicolored when said LCD operates in said transmissive mode.

34. The method as recited in claim 21 wherein said controllable CLC contains a twist agent that determines an intrinsic color of said controllable CLC.

35. The method as recited in claim 21 wherein said step of controlling comprises the step of providing a drive signal from a drive circuit to selectively place said controllable CLC in said "on" and said "off" states.

36. The method as recited in claim 21 wherein said controllable CLC is arranged in pixels, said step of controlling comprising the step of controlling each of said pixels independently to achieve said "on" and "off" states.

37. The method as recited in claim 21 wherein said first and second substrates contain a conductive matrix that provides a path for drive voltage to be conveyed to said controllable CLC.

38. The method as recited in claim 37 wherein said conductive matrix defines pixel locations of said controllable CLC.

39. The method as recited in claim 21 wherein said first and second substrates are substantially parallel.

40. The method as recited in claim 21 wherein said predetermined handedness is right-handed.

41. A method of manufacturing a cholesteric liquid crystal display (LCD), comprising the steps of:

locating a controllable cholesteric liquid crystal (CLC) between first and second substrates, said controllable CLC capable of selectively exhibiting an "on" state and an "off" state and having a circular polarity of a predetermined handedness when said controllable CLC is in said "on" state; and

locating a circular polarizer having a circular polarity of a particular handedness proximate said first substrate, said circular polarizer capable of cooperating with said controllable CLC to increase the difference between the relative brightness of said "on" state and said "off" state whereby a contrast ratio of said cholesteric LCD is increased.

42. The method as recited in claim 41 wherein said circular polarizer attenuates a substantial portion of light reflected from said first substrate.

43. The method as recited in claim 41 further comprising the steps of:

locating a second circular polarizer on an opposite side of said second substrate from said controllable CLC, said second circular polarizer having an arbitrary handedness; and

locating a reflector on an opposite side of said second circular polarizer from said second substrate, said second circular polarizer and said reflector cooperating to absorb light transmitted through said controllable CLC.

44. The method as recited in claim 41 wherein said predetermined handedness equals said particular handedness, said controllable CLC reflecting wavelengths of light corresponding to an intrinsic color of said controllable CLC and transmitting all other wavelengths of light when said controllable CLC is in said "on" state, said LCD adapted to cooperate with a projector to project said all other wavelengths of light when said controllable CLC is in said "on" state, said LCD scattering said light when said controllable CLC is in said "off" state.

45. The method as recited in claim 41 wherein said predetermined handedness is opposite said particular handedness, said LCD adapted to cooperate with a projector to project white light when said controllable CLC is in said "on" state, said LCD scattering said light when said controllable CLC is in said "off" state.

46. The method as recited in claim 45 further comprising the step of locating a color filter proximate said controllable CLC, said color filter causing said LCD to cooperate with said projector to project a colored light when said controllable CLC is in said "on" state, said LCD scattering said colored light when said controllable CLC is in said "off" state.

47. The method as recited in claim 46 wherein said color filter is a multicolor filter, said multicolor filter causing said LCD to cooperate with said projector to project a multicolored light when said controllable CLC is in said "on" state, said LCD scattering said colored light when said controllable CLC is in said "off" state.

48. The method as recited in claim 41 further comprising the step of locating a second circular polarizer on an opposite side of said second substrate from said controllable CLC, said second circular polarizer having a handedness that is opposite said predetermined handedness and said particular handedness, said second circular polarizer thereby blocking light transmitted through said controllable CLC when said controllable CLC is in said "on" state.

49. The method as recited in claim 48 further comprising the step of locating a color filter proximate said controllable CLC, said color filter causing said LCD to transmit a colored light when said controllable CLC is in said "off" state.

50. The method as recited in claim 49 wherein said color filter is a multicolor filter, said color filter causing said LCD to transmit a multicolored light when said controllable CLC is in said "off" state.

51. The method as recited in claim 41 further comprising the step of locating a polymer dispersed LC (PDLC) on an opposite side of said second substrate from said controllable CLC, said PDLC allowing said LCD to operate:

in a reflective mode wherein said PDLC is placed in an opaque state, and

in a transmissive mode wherein said PDLC is placed in a transparent state and light passing through said PDLC and said controllable CLC passes through said circular polarizer.

52. The method as recited in claim 51 further comprising the step of locating a color filter proximate said second substrate, said color filter causing said light to be a certain color when said LCD operates in said transmissive mode.

53. The method as recited in claim 52 wherein said color filter is a multicolor filter, said light being multicolored when said LCD operates in said transmissive mode.

54. The method as recited in claim 41 wherein said controllable CLC contains a twist agent that determines an intrinsic color of said controllable CLC.

55. The method as recited in claim 41 further comprising the step of providing a drive circuit that generates a drive signal to selectively place said controllable CLC in said "on" and said "off" states.

56. The method as recited in claim 41 further comprising the step of arranging said controllable CLC in pixels.

57. The method as recited in claim 41 further comprising the step of forming a conductive matrix on said first and second substrates, said conductive matrix providing a path for drive voltage to be conveyed to said controllable CLC.

58. The method as recited in claim 57 wherein said conductive matrix defines pixel locations of said controllable CLC.

59. The method as recited in claim 41 further comprising the step of arranging said first and second substrates to be substantially parallel.

60. The method as recited in claim 41 wherein said predetermined handedness is right-handed.