Optical router switch array and method for manufacture

• US 6,885,414 B1
• Filed: 10/01/2001
• Issued: 04/26/2005
• Est. Priority Date: 09/29/2000
• Status: Expired due to Fees

• Current Assignee: Kent Optronics, Inc.
• Original Assignee: Kent Optronics, Inc.
• Inventors: Li, Le
• Primary Examiner(s): CHOWDHURY, TARIFUR RASHID
• Application Number:
  US09/968,201
• Time in Patent Office: 1,303 Days
• Field of Search: 385 16- 23, 385/24, 385/10, 385/31, 385/36, 385/37, 359/1, 359/15, 359/34, 359/432, 349/175, 349/177, 349/185, 349/196, 349/74, 349/201, 349/113
• US Class Current: 349/74
• CPC Class Codes: G02F 1/133365 Cells in which the active layer comprises a liquid crystalline polymer
• 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 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• 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 2201/307 Reflective grating, i.e. Bragg grating
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

An optical router switch array includes a plurality of switchable mirror elements having holographic liquid crystal arranged in stack cells. Each of the mirror elements is isolated electrically from the other switchable mirror elements by a plurality of substrates alternative arranged between the switchable mirror elements. Holographic gratings are formed on the holographic liquid crystal by exposure to holography at predetermined incident angles. A single switchable mirror element can also be provided in cases where an array is not required. The switchable mirror elements are polarization insensitive, stable within the operational spectral region, and stable versus temperature. The invention also includes methods for manufacturing a single switchable mirror element and the optical arrray.

Claims

1. An optical router switch array comprising:

a plurality of switchable mirror elements for reflecting and transmitting an incident beam of light;

the plurality of switchable elements comprising a holographic liquid crystal in stacked cells;

said mirror elements having alternating liquid crystal polymer and LMWLC layers;

said mirror elements being disposed as side by side groups in each said stacked cell;

a pair of substrates sandwiching each stacked cell and thereby spacing the said side by side groups of mirror elements in the cell from side by side groups of mirror elements of other stacked cells; and

each one mirror element of said plurality of switchable mirror elements including pixilated electrodes at said sandwiching substrates that are electrically isolated from pixilated electrodes of other switchable mirror elements of said plurality of switchable mirror elements.

2. The device according to claim 1, wherein said holographic liquid crystal in each individual liquid crystal cell in the stacked cells is individually formed by exposing to holography prior to stacking at predetermined incident angles to form holographic gratings having a predetermined pattern.

3. The device according to claim 2, wherein the holographic gratings comprise Bragg gratings.

4. The device according to claim 3, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and the holographically formed patterns in the liquid crystal of the Bragg gratings are formed via multiple beams holographic exposure for tuning Bragg reflection according to variations in an electric field.

5. The device according to claim 3, wherein the Bragg gratings are formed by converging oppositely-directed laser beams in the liquid crystal of the stacked cells.

6. The device according to claim 2, wherein the holographic gratings are formed by converging oppositely-directed laser beams in the liquid crystal of the stacked cells.

7. The device according to claim 1, wherein said holographic liquid crystal in the stacked cells is formed by exposing the stacked cells to holography at predetermined incident angles to form holographic gratings having a predetermined pattern.

8. The device according to claims 7, wherein the orientation of the holographic gratings is in the same direction.

9. The device according to claim 8, wherein the holographic gratings comprise Bragg gratings.

10. The device according to claim 9, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and the holographically formed pattern in the liquid crystal of the Bragg gratings formed via multiple beam holographic exposure for tuning Bragg reflection according to variations in an electric field.

11. The device according to claim 9, wherein the liquid crystal of the Bragg grating are in nematic phase and the Bragg gratings are formed by converging oppositely-directed laser beams in the liquid crystal of the stacked cells.

12. The device according to claim 8, wherein the liquid crystal of the Bragg gratings are in nematic phase and the holographic gratings are formed by converging oppositely-directed laser beams in the liquid crystal of the slacked cells.

13. The device according to claims 7, wherein the mirror elements in the stacked cells are aligned parallel to each other.

14. The device according to claim 7, wherein the holographic gratings comprise Bragg gratings.

15. The device according to claim 14, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and the holographically formed patterns in the liquid crystal of the Bragg gratings formed via multiple beam holographic exposure for tuning Bragg reflection according to variations in an electric field.

16. The device according to claim 14, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and the Bragg gratings are formed by converging oppositely-directed laser beams in the liquid crystal of the stacked cells.

17. The device according to claim 7, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and the holographic gratings are formed by converging oppositely-directed laser beams in the liquid crystal of the stacked cells.

18. The device according to claim 7, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and said cholesteric liquid crystal comprises a composite material of a non-polymeric low molecular weight (LMW) material and liquid crystal polymer.

19. The device according to claim 17, wherein said composite material is included in a cell with rubbed polyimide.

20. The device according to claim 7, wherein the liquid crystal of the Bragg gratings are in cholesteric phase and said cholesteric liquid crystal consists of a composite material of non-polymeric low molecular weight (LMW) and a liquid crystal polymer.

21. The device according to claim 1, wherein the pixilated electrodes comprise Indium-Tin-Oxide (ITO).

22. The device according to claim 1, wherein the mirror elements in the stacked cells are aligned parallel to each other.

23. A method for manufacturing an optical router switch array comprising the steps of

(a) providing a plurality of switchable mirror elements comprising a liquid crystal housed in a plurality of stacked cells;

(b) providing a plurality of substrates which are alternately arranged with said stacked cells so that each one of said plurality of switchable mirror elements is arranged between two substrates of said plurality of substrates and separated from switchable mirror elements of all other stacked cells of said plurality of stacked cells;

(c) providing pixilated electrodes for said each one of said plurality of switchable mirror elements which are electrically insulated from pixilated electrodes of said all other mirror elements of said plurality of switchable mirror elements; and

(d) exposing the liquid crystal in the assembly resulting from performance of steps (a) through (c) to holography at predetermined angles from at least two incident beams to form holographic gratings having a predetermined pattern.

24. The method according to claim 23, wherein step (a) includes:

(i) stacking a plurality of empty cells;

(ii) aligning the empty cells stacked in step (i);

(iii) affixing the aligned stack of empty cells together; and

(iii) filling the empty cells with a liquid crystal mixture.

25. The method according to claims 23, wherein step (a) includes the substeps in any order of filling the cells with a liquid crystal mixture, stacking the cells, aligning the cells, and affixing the cells to each other.

26. The method according to claim 23, wherein the liquid crystal recited in step (a) is a cholesteric liquid crystal.

27. The method according to claim 26, wherein the mirror elements in said plurality of stacked cells are aligned parallel to each other.

28. The method according to claim 26, wherein the holographic liquid crystal comprises a mixture of cholesteric liquid crystal material and a pre-polymerized liquid crystal.

29. The method according to claim 28, wherein the holographic liquid crystal further comprises a chiral additive, and said pixilated substrates in step (c) comprises Indium-Tin-Oxide (ITO).

30. The method according to claim 26, wherein said plurality of substrates provided in step (b) comprise glass plates.

31. The method according to claim 26, wherein said plurality of substrates provided in step (b) comprise plastic plates.

32. The method according to claim 26, wherein the holographic gratings comprise Bragg gratings.

33. The method according to claim 32, wherein the Bragg gratings are formed in step (d) via multiple beam holographic exposure for tuning a Bragg reflection of said grating to respond to variations in an applied electric field.

34. The method according to claim 33, wherein power values used during multiple beam holographic exposure is different.

35. The method according to claim 26, wherein the number of beams used for holography in step (d) is two, and said beams being propagated in opposite direction that converge in the stacked cells.

36. The method according to claim 26, wherein said at least two beams originate from different light sources.

37. The method according to claim 26, wherein said at least two beams originate from a single beam of light and are split by a beam splitter.

38. The method according to claim 26, wherein said at least two beams originate from a single beam of light and pass through a spatial filter, a beam expander and a beam splitter.

39. The method according to claim 26, wherein said at least two beams originate from a single beam of light and pass through a spatial filter, a beam expander, a half-waveplate and a beam splitter.

40. The method according to claim 23, wherein the liquid crystal recited in step (a) is a nematic liquid crystal.

41. The method according to claim 40, wherein the mirror elements in said plurality of stacked cells are aligned parallel to each other.

42. The method according to claim 40, wherein the holographic gratings comprise Bragg gratings.

43. The method according to claim 42, wherein the Bragg gratings are formed in step (d) via multiple beam holographic exposure for tuning a Bragg reflection of said grating to respond to variations in an applied electric field.

44. The method according to claim 43, wherein power values used during multiple beam holographic exposure is different.

45. The method according to claim 40, wherein the number of beams used for holography in step (d) is two, and said beams being propagated in opposite direction that converge in the stacked cells.

46. The method according to claim 23, wherein the mirror elements in said plurality of stacked cells are aligned parallel to each other.

47. The method according to claims 23, wherein the holographic gratings comprise Bragg gratings.

48. The method according to claim 47, wherein the Bragg gratings are in step (d) formed via multiple beam holographic exposure for tuning a Bragg reflection of said grating to respond to variations in an applied electric field.

49. The method according to claim 48, wherein power values used during multiple beam holographic exposure is different.

50. The method according to claim 23, wherein the number of beams used for holography in step (d) is two, and said beams being propagated in opposite direction that converge in the stacked cells.

51. The method according to claim 23, wherein said at least two beams originate from different light sources.

52. The method according to claim 23, wherein said at least two beams originate from a single beam of light and are split.

53. The method according to claim 23, wherein said at least two beams originate from a single beam of light and pass through a spatial filter, a beam expander and a beam splitter.

54. The method according to claim 23, wherein said at least two beams originate from a single beam of light and pass through a spatial filter, a beam expander, a half-waveplate and a beam splitter.