Lateral electrode smectic liquid crystal devices

• US 5,493,426 A
• Filed: 05/03/1993
• Issued: 02/20/1996
• Est. Priority Date: 11/14/1991
• Status: Expired due to Fees

• Current Assignee: University of Colorado Foundation Inc (University of Colorado)
• Original Assignee: University of Colorado Foundation Inc (University of Colorado)
• Inventors: Sneh, Anat, Sharp, Gary D., Liu, Jian-Yu, Johnson, Kristina M.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): TRICE, RONALD
• Application Number:
  US08/056,415
• Time in Patent Office: 1,023 Days
• Field of Search: 359/40, 359/42, 359/53, 359/77, 359/87, 359/89, 359/93, 359/100
• US Class Current: 349/74
• 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

This invention provides smectic liquid crystal cells with lateral electrodes. The effective change in refractive index with field-induced tilting of the liquid crystal molecules is increased by providing an angle between the direction of propagation of light and the direction of the molecular directors at zero applied field. For homeotropically aligned liquid crystals this is accomplished by inclining the incident light beam at an oblique angle to the device surface. For tilted layer cells the liquid crystal layers are tilted and the light can impinge at normal incidence. This invention further provides Fabry-Perot filters utilizing lateral electrode liquid crystal cells.

Claims

1. A tilted layer liquid crystal cell for light modulation comprising:

a pair of substrates positioned with opposing surfaces spaced apart to form cell walls;

a smectic liquid crystal with rotatable optic axis disposed between said cell walls, the layers of said liquid crystal at an oblique angle, Θ

, to said cell walls; and

a means for applying an electric field parallel to said cell walls through said liquid crystal to rotate said optic axis of said liquid crystal;

wherein the light is transmitted through said liquid crystal.

2. The tilted layer cell of claim 1 further comprising an alignment layer on each of said cell walls.

3. The tilted layer cell of claim 2 wherein each of said alignment layers comprise obliquely deposited SiO_x.

4. The tilted layer cell of claim 3 wherein each of said alignment layers further comprises a homeotropic alignment agent coated on said SiO_x.

5. The tilted layer cell of claim 2 wherein Θ

is greater than 30° and

less than 60°

.

6. The tilted layer cell of claim 5 wherein Θ

is approximately 45°

.

7. The tilted layer cell of claim 5 wherein said liquid crystal is a SmA* liquid crystal and wherein said alignment layers comprise obliquely deposited SiO_x and a homeotropic alignment agent coated on said SiO_x.

8. The tilted layer cell of claim 1 wherein said electric field is both parallel to said cell walls and parallel to the smectic layers of said liquid crystal.

9. The tilted layer cell of claim 1 wherein said liquid crystal is selected from the group consisting of SmA*, SmC*, DHF, achiral ferroelectric and antiferroelectric liquid crystals.

10. The tilted layer cell of claim 1 wherein said liquid crystal is a SmA* liquid crystal.

11. The tilted layer cell of claim 1 wherein said means for applying an electric field comprises two electrodes disposed, laterally about said liquid crystal.

12. The tilted layer cell of claim 11 wherein said electrodes further provide a means for spacing apart said substrates.

13. The tilted layer cell of claim 1 disposed as a pixel in a multipixel array of modulators.

14. The tilted layer cell of claim 1 wherein said light is incident on said cell at substantially normal incidence.

15. The tilted layer cell of claim 1 wherein rotating said optic axis modulates the extraordinary index of refraction of said liquid crystal.

16. The tilted layer cell of claim 15 wherein modulating said extraordinary index of refraction modulates the phase of light transmitted through said liquid crystal.

17. The tilted layer cell of claim 1 wherein said cell is a variable retarder.

18. A method of phase modulation of light utilizing the tilted layer cell of claim 1 and comprising the steps of:

impinging light on the tilted layer cell of claim 1; and

applying an electric field to said cell, whereby the phase of said light is modulated.

19. The method of phase modulation of claim 18 wherein said light impinges at substantially normal incidence.

20. The method of phase modulation of claim 18 wherein said impinging light is linearly polarized and wherein the polarization vector is in the plane of rotation of said optic axis of said liquid crystal.

21. A Fabry-Perot modulator for light comprising:

a first liquid crystal cell comprising a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal disposed between said cell walls, and a means for applying an electric field parallel to said cell walls through said liquid crystal; and

a front and a back reflective means positioned in series with and on either side of said liquid crystal to form a Fabry-Perot cavity.

22. The Fabry-Perot modulator of claim 21 wherein said liquid crystal is a homeotropically aligned liquid crystal.

23. The Fabry-Perot modulator of claim 21 wherein said liquid crystal is a tilted layer aligned liquid crystal having the layers of said liquid crystals at an oblique angle to said cell walls.

24. The Fabry-Perot modulator of claim 23 wherein said liquid crystal is a SmA* liquid crystal.

25. The Fabry-Perot modulator of claim 24 wherein said liquid crystal cell further includes an alignment layer on each of said cell walls, each of said alignment layers comprising obliquely deposited SiO_x.

26. The Fabry-Perot modulator of claim 25 wherein each of said alignment layers further comprises a homeotropic alignment agent coated on said SiO_x.

27. The Fabry-Perot modulator of claim 21 wherein said liquid crystal is selected from the group consisting of SmA*, SmC*, DHF, achiral ferroelectric and antiferroelectric liquid crystals.

28. The Fabry-Perot modulator of claim 21 wherein said liquid crystal is a SmA* liquid crystal.

29. The Fabry-Perot modulator of claim 21 wherein the reflectivities of said front and back reflective means are such that the modulator operates in transmission-reflection mode.

30. The Fabry-Perot modulator of claim 21 wherein the reflectivities of said front and back reflective means are such that the modulator operates in reflection-only mode.

31. The Fabry-Perot modulator of claim 21 further including an isotropic spacer positioned between said front and back reflective means.

32. The Fabry-Perot modulator of claim 21 adapted for use with an optical addressing signal and further comprising a photosensing means, optically coupled with said addressing signal and electrically connected with said electric field applying means, for varying the applied electric field in response to said addressing signal.

33. The Fabry-Perot modulator of claim 21 disposed as a pixel in a multipixel array of Fabry-Perot modulators.

34. The Fabry-Perot modulator of claim 21 further comprising a second liquid crystal cell, positioned in series with said first liquid crystal cell and between said front and back reflective means, comprising a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal disposed between said cell walls, and a means for applying an electric field parallel to said cell walls through said liquid crystal, wherein the electric field in said second liquid crystal cell is orthogonal to the electric field in said first liquid crystal cell.

35. The Fabry-Perot modulator of claim 34 wherein said first and second liquid crystal cells have equal magnitude retardances.

36. The Fabry-Perot modulator of claim 34 further comprising:

a second liquid crystal cell, positioned in parallel with said first liquid crystal cell and between said front and back reflective means, comprising a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal disposed between said cell walls, and a means for applying an electric field parallel to said cell walls through said liquid crystal, wherein the electric field in said second liquid crystal cell is orthogonal to the electric field in said first liquid crystal cell.

a means for spatially dividing said light into a first and a second component of orthogonal polarization and for coupling said first component into said first liquid crystal cell and said second component into said second liquid crystal cell; and

a means for receiving and for recombining light from said first and said second liquid crystal cells.

37. The Fabry-Perot modulator of claim 36 wherein said first and second liquid crystal cells have equal magnitude retardances.

38. The Fabry-Perot modulator of claim 21 wherein said light is incident on said front reflective means at substantially normal incidence.

39. The Fabry-Perot modulator of claim 21 wherein applying said electric field rotates the optic axis of said liquid crystal.

40. The Fabry-Perot modulator of claim 39 wherein rotating said optic axis modulates the extraordinary index of refraction of said liquid crystal.

41. The Fabry-Perot modulator of claim 40 wherein modulating said extraordinary index of refraction modulates the phase of light transmitted through said liquid crystal.

42. A prism-coupled modulator for light comprising:

a first and a second substrate positioned with opposing surfaces spaced apart to form cell walls;

a smectic liquid crystal with rotatable optic axis disposed between said cell walls;

a means for applying an electric field parallel to said cell walls through said liquid crystal to rotate said optic axis of said liquid crystal; and

an input prism for receiving said light and for optically coupling the received light with said first substrate at an angle oblique to said first substrate, wherein said received light is transmitted through said liquid crystal.

43. The prism-coupled modulator of claim 42 further including an output prism for receiving the transmitted light from said second substrate and for outputting said transmitted light at an angle oblique to said second substrate.

44. The prism-coupled modulator of claim 43 wherein said input and output prisms are right angle prisms positioned with hypotenuse faces facing said first and second substrates, respectively.

45. The prism-coupled modulator of claim 44 wherein said input and output prisms further function as said first and second substrates, respectively.

46. The prism-coupled modulator of claim 42 wherein said liquid crystal is a homeotropically aligned liquid crystal.

47. The prism-coupled modulator of claim 42 wherein said liquid crystal is a tilted layer aligned liquid crystal having the layers of said liquid crystals at an oblique angle to said cell walls.

48. The prism-coupled modulator of claim 42 wherein rotating said optic axis modulates the extraordinary index of refraction of said liquid crystal.

49. The prism-coupled modulator of claim 48 wherein modulating said extraordinary index of refraction modulates the phase of light transmitted through said liquid crystal.

50. A series polarization independent modulator of light comprising:

a first smectic liquid crystal cell for variably retarding a first polarization of light; and

a second smectic liquid crystal cell, positioned in series with said first cell, for variably retarding a second polarization of light, said second polarization orthogonal to said first linear polarization;

wherein each of said liquid crystal cells comprises a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal layer with rotatable optic axis disposed between said cell walls, and a means for applying an electric field parallel to said cell walls through said liquid crystal layer; and

wherein said electric field in said first liquid crystal cell is orthogonal to said electric field in said second liquid crystal cell.

51. The series polarization independent modulator of claim 50 wherein said liquid crystal in said first and second liquid crystal cells is homeotropically aligned.

52. The series polarization independent modulator of claim 50 wherein said liquid crystals in said first and second liquid crystal cells are tilted layer aligned liquid crystals having the layers of said liquid crystals in each of said cells at an oblique angle to said cell walls, and wherein the smectic layers in each cell are parallel to the electric-field in that cell.

53. The series polarization independent modulator of claim 50 wherein said liquid crystal in said first and second liquid crystal cells is a SmA* liquid crystal.

54. The series polarization independent modulator of claim 50 wherein said first and second liquid crystal cells have equal magnitude retardances.

55. The series polarization independent modulator of claim 50 wherein said first and said second liquid crystal cells share one substrate in common, such that said series polarization independent modulator comprises three substrates in series.

56. The series polarization independent modulator of claim 55 wherein said liquid crystal in said first and second liquid crystal cells is a tilted layer aligned SmA* liquid crystal having the layers of said liquid crystals at oblique angles to said cell walls, and wherein the smectic layers of each cell are parallel to the electric field in that cell.

57. The series polarization independent modulator of claim 50 further comprising a first and a second reflective means forming a Fabry-Perot cavity containing said liquid crystal layers in said first and second liquid crystal cells.

58. A parallel polarization diversity modulator for light comprising:

a means for spatially dividing said light into a first and a second component of orthogonal polarization;

a first liquid crystal cell optically coupled with said first component of light;

a second liquid crystal cell optically coupled with said second component of light; and

a means for recombining said first and said second component of light;

each of said first and second liquid crystal cells comprising a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal disposed between said cell walls, and a means for applying an electric field parallel to said cell walls through said liquid crystal; and

wherein said electric field in said first liquid crystal cell is orthogonal to said electric field in said second liquid crystal cell.

59. The parallel polarization diversity modulator of claim 58 wherein said first and said second liquid crystal cells have equal magnitude retardances.

60. The parallel polarization diversity modulator of claim 58 wherein said liquid crystals in said first and said second liquid crystal cells are homeotropically aligned.

61. The parallel polarization diversity modulator of claim 58 wherein said liquid crystals in said first and said second liquid crystal cells are tilted layer aligned having the layers of said liquid crystals in each of said cells at an oblique angle to said cell walls, and wherein the smectic layers of each cell are parallel to the electric field in that cell.

62. The parallel polarization diversity modulator of claim 58 adapted for use with an optical fiber and further including a means for optically coupling said modulator with said fiber.

63. The parallel polarization diversity modulator of claim 58 wherein each of said first and second liquid crystal cells further includes a first and a second reflective means positioned in series with and on either side of said liquid crystal to form a Fabry-Perot cavity containing said liquid crystal.

64. The parallel polarization diversity modulator of claim 63 adapted for use with an optical fiber and further including a means for optically coupling said modulator with said fiber.

65. The parallel polarization diversity modulator of claim 64 wherein said liquid crystals in said first and said second liquid crystal cells are tilted layer aligned having the layers of said liquid crystals at oblique angles to said cell walls, and wherein the smectic layers of each cell are parallel to the electric field in that cell.

66. The parallel polarization diversity modulator of claim 58 wherein said liquid crystal is selected from the group consisting of SmA*, SmC*, DHF, achiral ferroelectric and antiferroelectric liquid crystals.

67. The parallel polarization diversity modulator of claim 58 wherein said liquid crystal is a SmA* liquid crystal.

68. The parallel polarization diversity modulator of claim 58 wherein said first and second liquid crystal cells share both substrates in common.

69. The parallel polarization diversity modulator of claim 68 wherein said means for dividing light and said means for recombining light comprise birefringent crystals and wherein said birefringent crystals form said substrates.

70. The parallel polarization diversity modulator of claim 69 adapted for use with an optical fiber and further including a means for optically coupling said modulator with said fiber.

71. An edge-entering liquid crystal modulator for light comprising a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal disposed between said cell walls, and a means for applying an electric field to said liquid crystal, wherein said modulator is adapted to receive light incident on the edge of said modulator between said substrates, and wherein the application of said electric field causes phase modulation of light transmitted through said modulator.

72. The edge-entering modulator of claim 71 wherein said means for applying an electric field comprises lateral electrodes for applying an electric field parallel to said cell walls.

73. The edge-entering modulator of claim 72 wherein said liquid crystal is a homeotropically aligned liquid crystal.

74. The edge-entering modulator of claim 72 wherein said liquid crystal is a tilted layer aligned liquid crystal having the layers of said liquid crystal at an oblique angle to said cell walls.

75. The edge-entering modulator of claim 71 wherein said means for applying an electric field comprises planar electrodes for applying an electric field normal to said cell walls.

76. The edge-entering modulator of claim 75 wherein said liquid crystal is a planar aligned liquid crystal.

77. The edge-entering modulator of claim 71 further including a second liquid crystal modulator positioned in series with said edge-entering modulator, said second modulator comprising a pair of substrates with opposing surfaces spaced apart to form cell walls, a smectic liquid crystal disposed between said cell walls, and a means for applying an electric field to said liquid crystal.

78. The edge-entering modulator of claim 77 wherein the electric field in said second modulator is applied orthogonal to the electric field in said edge-entering modulator.

79. The edge-entering modulator of claim 77 wherein said second modulator is oriented to receive light incident on the edge of said second modulator between said substrates.

80. The edge entering modulator of claim 77 wherein said second modulator is oriented to receive light through said cell walls.

81. A method of phase modulation of linearly polarized light comprising the steps of:

providing a liquid crystal cell comprising;

a pair of substrates positioned with opposing surfaces spaced apart to form cell walls;

a homeotropically aligned smectic liquid crystal with rotatable optic axis disposed between said opposing surfaces, said liquid crystal having a plane of electric field-induced rotation; and

a means for applying an electric field parallel,to said opposing surfaces across said liquid crystal to rotate said optic axis of said liquid crystal;

orienting said cell to receive the incident light with the normal to said substrates at an angle 8 to the propagation vector of said incident light and with said plane of rotation of said liquid crystal parallel to the polarization of said incident light; and

applying an electric field across said liquid crystal, whereby the phase of said incident light is modulated.

82. The method of phase modulation of claim 81 wherein said liquid crystal is selected from the group consisting of SmA*, SmC*, DHF, achiral ferroelectric and antiferroelectric liquid crystals.

83. The method of phase modulation of claim 81 wherein said liquid crystal is a SmA* liquid crystal.

84. The method of phase modulation of claim 81 wherein Θ

=0°

.

85. The method of phase modulation of claim 81 wherein Θ

is greater than 0°

.

86. The method of phase modulation of claim 81 wherein Θ

is greater than 30° and

less than 60°

.