Reflective optically active diffractive device

• US 5,825,448 A
• Filed: 11/05/1996
• Issued: 10/20/1998
• Est. Priority Date: 05/19/1995
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Smith, Brett E., Johnson, deceased, David L., Chen, Jianmin, Glenn, William E., Bos, Philip J., Holton, Carvel E.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): DUDEK, JAMES A
• Application Number:
  US08/743,962
• Time in Patent Office: 714 Days
• Field of Search: 349/127, 349/126, 349/128, 349/129, 349/130
• US Class Current: 349/128
• CPC Class Codes: G02F 1/133753 with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 1/292 by controlled diffraction or phased-array beam steering controlled diffraction for optical switching G02F1/31
• CPC Class Codes: G02F 2201/305 diffraction grating
• CPC Class Codes: G02F 2203/48 Variable attenuator

Abstract

A reflective liquid crystalline diffractive light valve for use in a diffractive projection system. The liquid crystal cell includes a transparent substrate and a reflective substrate treated to provide alternating stripes which cooperate with the liquid crystal to form liquid crystal domains extending across the thickness of the cell that will produce an appropriate phase difference in light reflected by the cell, irrespective of the polarization of incident light. The techniques embodied in the present invention are applicable to the creation of electrically controllable diffractive optical elements for ray optic, integrated optic or fiber optic utilization operated in either transmission or reflection. Diffractive patterns may be lithographically, holographically or interferometrically generated.

Claims

1. A liquid crystalline diffractive light modulating device comprising nematic liquid crystal material disposed between first and second substrates defining cell walls and including means for addressing said liquid crystal material, said first substrate being treated to provide a plurality of domains in which the liquid crystal adjacent said first substrate in a first of said domains is projected in a different direction than the liquid crystal adjacent said first substrate in a second of said domains, said substrates cooperating with said liquid crystal to form a plurality of liquid crystal domains extending between said first and second substrates wherein the alignment of the liquid crystal adjacent said second substrate is different than the alignment of said liquid crystal adjacent said first substrate, whereby light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates and exits said first and second domains through one said substrate out of phase, irrespective of the polarization of said incident light.

2. The device according to claim 1 wherein, in said first and second domains, there is an approximately 90°

difference in the projection on the cell surface of a liquid crystal director of the liquid crystal approximately midway between said substrates, wherein light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates out of phase, irrespective of the polarization of said incident light.

3. The device according to claim 1 wherein said means for addressing said liquid crystal material include a continuous transparent electrode disposed on said first substrate.

4. The device according to claim 1 wherein said domains are arranged in alternating stripes on said first substrate extending substantially across the entire light modulating portion of said device.

5. The device according to claim 1 wherein the liquid crystal adjacent one of said substrates in said first domain is tilted at an angle different than the liquid crystal adjacent said one substrates in said second domain.

6. The device according to claim 1 wherein the liquid crystal adjacent each said first and second substrate are tilted at different angles in each respective domain.

7. The device according to claim 1, wherein the liquid crystal aligned such that the projection of the directors on the cell surface of the liquid crystal adjacent said first substrate in one of said first and second domains are oriented substantially orthogonally to the projection of the directors on the cell surface of the liquid crystal adjacent said first substrate in the other of said domains.

8. The device according to claim 7, wherein the liquid crystal are aligned such that the projection of the directors on the cell surface of the liquid crystal adjacent said second substrate in one of said first and second domains are oriented substantially orthogonally to the projection of the directors on the cell surface of the liquid crystal adjacent said second substrate in the other of said domains.

9. The device according to claim 8, wherein the liquid crystal in said first and second domains have opposite rotational twist sense.

10. The device according to claim 8, wherein the liquid crystal in said first and second domains have the same rotational twist sense.

11. The device according to claim 1 wherein the liquid crystal molecules at the surface of said first substrate in said first and second domains are tilted toward each other, and the liquid crystal molecules at the surface of said second substrate are oriented orthogonal to the liquid crystal molecules adjacent said first substrate and have a first pretilt angle in said first domain and a second pretilt angle different from said first pretilt angle, in said second domain, whereby in said first and second domains the liquid crystal exhibits a twisted nematic liquid crystal structure having opposite twist sense extending between said first and second substrates.

12. The device according to claim 1 wherein the liquid crystal molecules at the surface of said first substrate in said first and second domains are tilted away from each other and the liquid crystal molecules at the surface of said second substrate are oriented orthogonal to the liquid crystal molecules adjacent said first substrate and have a first pretilt angle in said first domain and a second pretilt angle, different from said first pretilt angle, in said second domain, whereby in said first and second domains the liquid crystal exhibits a twisted nematic liquid crystal structure having opposite twist sense extending between said first and second substrates.

13. A liquid crystalline diffractive light modulating device comprising nematic liquid crystal material disposed between first and second substrates defining cell walls and including means for addressing said liquid crystal material, said first substrate being treated to provide a plurality of first and second domains in which the liquid crystal material adjacent said first substrate in a first of said domains is projected in a different direction than the liquid crystal adjacent said first substrate in a second of said domains, said first domain having a first pretilt angle different than a second pretilt angle in said second domain, whereby light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates and exits said first and second domains through the one said substrate out of phase, irrespective of the polarization of said incident light.

14. The device according to claim 13 wherein, in said first and second domains, there is an approximately 90°

difference in the projection on the cell surface of the liquid crystal director of the liquid crystal approximately midway between said substrates, whereby light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates out of phase, irrespective of the polarization of said incident light.

15. The device according to claim 13 wherein said domains are arranged in alternating stripes on said first substrate extending substantially across the entire light modulating portion of said device.

16. The device according to claim 13 wherein the liquid crystal molecules at the surface of said first substrate in said first and second domains are tilted toward each other.

17. The device according to claim 13 wherein the liquid crystal molecules at the surface of said first substrate in said first and second domains are tilted away from each other.

18. The device according to claim 13 wherein said means for addressing said liquid crystal material includes a continuous transparent electrode disposed on one of said first and second substrates.

19. The device according to claim 13 wherein said means for addressing said liquid crystal includes an active matrix disposed on said reflective substrate.

20. The device according to claim 13 wherein said first and second pretilt angles are provided with respect to said first substrate.

21. The device according to claim 13 wherein said second substrate being treated to provide said first domain with a third pretilt angle with respect to said second substrate different than a fourth pretilt angle in said second domain with respect to said second substrate.

22. A liquid crystalline diffractive light modulating device comprising nematic liquid crystal material disposed between first and second substrates defining cell walls and including means for addressing said liquid crystal material, said first and second substrates being treated to provide a plurality of domains in which the projection of the directors in a first domain are orthogonal to the projection directors in the second domain, wherein light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates and exits said first and second domains with about a half wave relative phase shift, irrespective of the polarization of said incident light.

23. The device according to claim 22, wherein the liquid crystal projectors adjacent said first substrate in said first domain are substantially orthogonal to the liquid crystal projectors adjacent said first substrate in said second domain and wherein the liquid crystal projectors adjacent said second substrate in said first domain are substantially orthogonal to the liquid crystal directors adjacent said second substrate in said second domain.

24. The device according to claim 23, wherein the liquid crystal projectors in said first and second domains have the same rotational twist sense.

25. The device according to claim 23, wherein the liquid crystal projectors in said first and second domains have opposite rotational twist sense.

26. The device according to claim 22, wherein the liquid crystal projectors in said first and second domains have the same rotational twist sense.

27. The device according to claim 22, wherein the liquid crystal projectors in said first and second domains have opposite rotational twist sense.

28. The device according to claim 22 wherein said means for addressing said liquid crystal material include a continuous transparent electrode disposed on said first substrate.

29. The device according to claim 22 wherein said domains are arranged in alternating stripes on said first substrate extending substantially across the entire light modulating portion of said device.

30. The device according to claim 22 wherein the liquid crystal in each said first and second domain adjacent said first substrate is tilted at an angle of from about 0.5°

to about 25°

with respect to said substrate.

31. The device according to claim 22 wherein the liquid crystal in each said first and second domain adjacent each said first and second substrate are tilted at an angle of from about 0.5°

to about 25°

with respect to said substrate.

32. The device according to claim 22 wherein said means for addressing said liquid crystal includes an active matrix disposed on said second substrate.

33. A method of making a liquid crystalline diffractive device comprising:

a) providing first and second substrates to define cell walls, and including means for addressing a liquid crystal material;

b) treating said first substrate with a first alignment layer to provide at least first and second domains adapted to promote different orientations of a liquid crystal material in said domains;

c) treating said second substrate with a second alignment layer adapted to promote an orientation of a liquid crystal adjacent said second substrate that is different than the orientation promoted by said first and second domains of said first substrate, and to cooperate with said first alignment layer and a liquid crystal disposed therebetween, to produce liquid crystal domains extending between said substrates; and

,

d) disposing a nematic liquid crystal material between said substrates to form liquid crystal domains extending between said substrates,

whereby light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates and exits said first and second domains through one said substrate out of phase.

34. The method according to claim 33 comprising treating said first substrate such that said first and second domains of said first alignment layer promote a homogeneous or a tilted homeotropic alignment of adjacent liquid crystal molecules in which said molecules in said first and second domains tilt in the opposite directions.

35. The method according to claim 33 comprising treating said first substrate such that said first and second domains of said first alignment layer promote a homogeneous or a tilted homeotropic alignment of adjacent liquid crystal molecules in which the projection on the cell surface of the directors of said molecules in said first and second domains are orthogonal.

36. The method according to claim 33 comprising treating said first substrate wherein the liquid crystal molecules are aligned such that the projection of the directors on the cell surface of the liquid crystal adjacent said first substrate in one of said first and second domains are oriented substantially orthogonally to the projection of the directors on the cell surface of the liquid crystal adjacent said first substrate in the other of said domains.

37. The method according to claim 36, comprising treating said second substrate wherein the liquid crystal molecules are aligned such that the projection of the directors on the cell surface of the liquid crystal adjacent said second substrate in one of said first and second domains are oriented substantially orthogonally to the projection of the directors on the cell surface of the liquid crystal adjacent said second substrate in the other of said domains.

38. The method according to claim 37, further comprising treating said substrates wherein the liquid crystal molecules in said first and second domains have opposite rotational twist sense.

39. The method according to claim 37, further comprising treating said substrates wherein the liquid crystal molecules in said first and second domains have the same rotational twist sense.

40. The method according to claim 37 wherein said treating of said first substrate comprises coating said substrate with polyimide, unidirectionally rubbing said substrate, masking at least a portion of said substrate and, thereafter, unidirectionally rubbing said substrate in the opposite direction.

41. The method according to claim 37 wherein said treating of said first substrate comprising obliquely evaporating a silicon oxide onto the surface of said substrate, masking at least a portion of said substrate and, thereafter, obliquely evaporating said silicon oxide the opposite direction to said first evaporation.

42. A method of making a liquid crystalline diffractive device comprising:

a) providing first and second substrates to define cell walls, and including means for addressing a liquid crystal material;

b) treating said first substrate with a first alignment layer to provide a plurality of domains in which a first said domain will promote an orientation of a liquid crystal material in said first domain orthogonally to a liquid crystal orientation promoted by said second domain;

c) treating said second substrate with a second alignment layer adapted to cooperate with said first alignment layer and a liquid crystal disposed therebetween, to produce first and second twisted nematic liquid crystal domains having opposite twist sense extending between said substrates; and

,

d) disposing a nematic liquid crystal material between said substrates to form first and second liquid crystal domains extending between said substrates in which the projection of the directors on the substrate surface, of the liquid crystal in said first and second domains is substantially orthogonal,

whereby light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates and exits said first and second domains through the one said substrate out of phase.

43. The method according to claim 42 wherein said second substrate is treated to promote homeotropic alignment of said liquid crystal material.

44. The method according to claim 42 wherein said treating of said first substrate comprises coating said substrate with polyimide, unidirectionally rubbing said substrate, masking at least a portion of said substrate and, thereafter, unidirectionally rubbing said substrate in a direction perpendicular to said first rub.

45. The method according to claim 42 wherein said treating of said first substrate comprising obliquely evaporating a silicon oxide of the formula SiO_X, wherein x is an integer from one to three, onto the surface of said substrate, masking at least a portion of said substrate and, thereafter, obliquely evaporating said silicon oxide orthogonally to said first evaporation.

46. The method according to claim 42 comprising treating said first substrate wherein the liquid crystal molecules are aligned such that the projection of the directors on the cell surface of the liquid crystal adjacent said first substrate in one of said first and second domains are oriented substantially orthogonally to the projection of the directors on the cell surface of the liquid crystal adjacent said first substrate in the other of said domains.

47. The device according to claim 42, comprising treating said second substrate wherein the liquid crystal molecules are aligned such that the projection of the directors on the cell surface of the liquid crystal adjacent said second substrate in one of said first and second domains are oriented substantially orthogonally to the projection of the directors on the cell surface of the liquid crystal adjacent said second substrate in the other of said domains.

48. The device according to claim 47, further comprising treating said substrates wherein the liquid crystal molecules in said first and second domains have opposite rotational twist sense.

49. The device according to claim 47, further comprising treating said substrates wherein the liquid crystal molecules in said first and second domains have the same rotational twist sense.

50. A method of making a liquid crystalline diffractive device comprising:

a) providing first and second substrates to define cell walls, and including means for addressing a liquid crystal material;

b) treating said first substrate with a first alignment layer to provide a plurality of domains in which a first said domain will promote a first pretilt orientation of said liquid crystal material and a second pretilt orientation of said liquid crystal material, different than said first pretilt orientation in said second domain;

c) treating said second substrate with a second alignment layer adapted to cooperate with said first alignment layer and a liquid crystal disposed therebetween, to produce first and second twisted nematic liquid crystal domains having opposite twist sense extending between said substrates; and

,

d) disposing a nematic liquid crystal material between said substrates to form first and second liquid crystal domains extending between said substrates in which the projection of the directors on the substrate surface, of the liquid crystal in said first and second domains is substantially orthogonal,

whereby light incident on said first and second domains through one said substrate and in phase, is reflected by the other of said substrates and exits said first and second domains through the one said substrate out of phase.

51. The method according to claim 50 wherein by treating said first substrate, said first and second pretilt orientations are provided with respect to said first substrate.

52. The method according to claim 51 wherein by treating said second substrate in said first domain a third pretilt orientation with respect to said second substrate different than a fourth pretilt angle in said second domain with respect to said second substrate is provided.

53. A liquid crystalline diffractive light modulating device comprising nematic liquid crystal material disposed between first and second substrates defining cell walls, wherein at least one of said substrates is transparent and including means for addressing said liquid crystal material, said first substrate being treated to provide a plurality of domains in which the liquid crystal adjacent said first substrate in a first of said domains is projected in a different direction than the liquid crystal adjacent said first substrate in a second of said domains, said substrates cooperating with said liquid crystal to form a plurality of liquid crystal domains extending between said first and second substrates wherein the alignment of the liquid crystal adjacent said second substrate is different than the alignment of said liquid crystal adjacent said first substrate, whereby light incident on said first and second domains through one said substrate and in phase, exits said first and second domains through one of said substrates out of phase, irrespective of the polarization of said incident light.

54. The device according to claim 53 wherein said first substrate is substantially parallel with one end of an optical fiber and said second substrate is substantially parallel with one end of a second optical fiber.

55. The device according to claim 53 wherein said first and second substrates are substantially orthogonal with respect to ends of optical fibers.

56. A method of making a liquid crystalline diffractive device comprising:

a) providing first and second substrates to define cell walls, wherein one of said first and second substrates is transparent and including means for addressing a liquid crystal material;

b) treating said first substrate with a first alignment layer to provide at least first and second domains adapted to promote different orientations of a liquid crystal material in said domains;

c) treating said second substrate with a second alignment layer adapted to promote an orientation of a liquid crystal adjacent said second substrate that is different than the orientation promoted by said first and second domains of said first substrate, and to cooperate with said first alignment layer and a liquid crystal disposed therebetween, to produce liquid crystal domains extending between said substrates; and

,

d) disposing a nematic liquid crystal material between said substrates to form liquid crystal domains extending between said substrates,

whereby light incident on said first and second domains through one of said substrates and in phase, exits said first and second domains through one of said substrates out of phase.

57. The method according to claim 56 further comprising the step of disposing one of said substrates adjacent to one end of an optical fiber and the other of said substrates adjacent one end of a second optical fiber.

58. The method according to claim 56 further comprising the step of disposing orthogonally with respect to the ends of optical fibers.