Electrically switchable polymer-dispersed liquid crystal materials including switchable optical couplers and reconfigurable optical interconnects

• US 6,821,457 B1
• Filed: 07/29/1999
• Issued: 11/23/2004
• Est. Priority Date: 07/29/1998
• Status: Expired due to Term

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Tondiglia, Vince P., Sutherland, Richard L., Epling, Bob, Natarajan, Lalgudi V., Bunning, Timothy J., Brandelik, Donna M.
• Primary Examiner(s): WU, SHEAN CHIU
• Application Number:
  US09/363,169
• Time in Patent Office: 1,944 Days
• Field of Search: 252/582, 252/299.01, 430/1, 430/2, 430/20, 359/15, 349/64, 349/112, 385/15, 385/16, 385/18, 385/27, 385/37
• US Class Current: 252/582
• CPC Class Codes: C09K 2323/00 Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/2713 cascade of polarisation selective or adjusting operations
• CPC Class Codes: G02B 6/2931 Diffractive element operating in reflection
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/29314 by moving or modifying the diffractive element, e.g. deforming
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 2201/305 diffraction grating
• CPC Class Codes: G03H 1/0005 Adaptation of holography to specific applications holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/0248 Volume holograms
• CPC Class Codes: G03H 2001/026 Recording materials or recording processes G03H2226/11 takes precedence; corresponding details, see subgroups of G03H2260/00
• CPC Class Codes: G03H 2001/0264 Organic recording material
• CPC Class Codes: G03H 2001/2615 in physical contact, i.e. layered holograms
• CPC Class Codes: G03H 2260/12 Photopolymer
• CPC Class Codes: G03H 2260/33 Having dispersed compound

Abstract

A new photopolymerizable material allows single-step, fast recording of volume holograms with properties that can be electrically controlled. Polymer-dispersed liquid crystals (PDLCs) in accordance with the invention preferably comprise a homogeneous mixture of a nematic liquid crystal and a multifunctional pentaacrylate monomer in combination with photoinitiator, coinitiator and cross-linking agent. Optionally, a surfactant such as octancic acid may also be added. The PDLC material is exposed to coherent light to produce an interference pattern inside the material. Photopolymerization of the new PDLC material produces a hologram of clearly separated liquid crystal domains and cured polymer domains. Volume transmission gratings made with the new PDLC material can be electrically switched between nearly 100% diffraction efficiency and nearly 0% diffraction efficiency. By increasing the frequency of the switching voltage, switching voltages in the range of 50 Vrms can be achieved. The optional use of a surfactant allows low switching voltages at lower frequencies than without a surfactant. In an alternative embodiment, a PDLC material in accordance with the invention can be utilized to form reflection gratings, including switchable reflection gratings. In still further embodiments, a PDLC material in accordance with the invention can be used to form switchable subwavelength gratings. By further processing, static transmission, reflection, and subwavelength PDLC materials can be formed. In addition, PDLC materials in accordance with the present invention can be used to form switchable slanted transmission gratings suitable for switchable optical coupling and reconfigurable optical interconnects.

Claims

1. A switchable slanted transmission grating comprising a polymer-dispersed liquid crystal material disposed between at least two optically transparent electrode plates, wherein the polymer-dispersed liquid crystal material is constructed by exposing to light in an interference pattern a mixture comprising, before exposure:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one liquid crystal;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

2. The switchable slanted transmission grating according to claim 1, wherein the polymerizable monomer comprises a mixture of di-, tri-, tetra-, and pentaacrylates.

3. The switchable slanted transmission grating according to claim 2, wherein the polymerizable monomer is at least one acrylate selected from the group consisting of triethyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, and dipentaerythritol pentaacrylate.

4. The switchable slanted transmission grating according to claim 3, wherein the polymerizable monomer comprises a mixture of tri- and pentaacrylates.

5. The switchable slanted transmission grating according to claim 4, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

6. The switchable slanted transmission grating according to claim 1, wherein the at least one liquid crystal is at least one liquid crystal selected from the group consisting of a mixture of cyanobiphenyls, 4′

-n-pentyl-cyanobiphenyl, 4′

-n-heptyl-4-cyanobiphenyl, 4′

-octaoxy-4-cyanobiphenyl, 4′

-pentyl-4-cyanoterphenyl, and α

-methoxybenzylidene-4′

-butylaniline.

7. The switchable slanted transmission grating according to claim 6, wherein the at least one liquid crystal comprises a mixture of cyanobiphenyls.

8. The switchable slanted transmission grating according to claim 1, wherein the chain-extending monomer is at least one member selected from the group consisting of N-vinyl pyrrolidone, N-vinyl pyridine, acrylonitrile, and N-vinyl carbazole.

9. The switchable slanted transmission grating according to claim 8, wherein the chain-extending monomer is N-vinyl pyrrolidone.

10. The switchable slanted transmission grating according to claim 1, wherein the coinitiator is at least one member selected from the group consisting of N-phenylglycine, triethylene amine, triethanolamine, and N,N-dimethyl-2,6-diisopropyl aniline.

11. The switchable slanted transmission grating according to claim 10, wherein the coinitiator is N-phenylglycine.

12. The switchable slanted transmission grating according to claim 1, wherein the photoinitiator is at least one member selected from the group consisting of rose bengal ester, rose bengal sodium salt, eosin, eosin sodium salt, 4,5-diiodosuccinyl fluorescein, camphorquinone, methylene blue, cationic cyanine dyes with trialkylborate anions, and merocyanine dyes derived from spiropyran.

13. The switchable slanted transmission grating according to claim 12, wherein the photoinitiator is rose bengal sodium salt.

14. The switchable slanted transmission grating according to claim 1, wherein the polymer-dispersed liquid crystal material, before exposure, further comprises a surfactant.

15. The switchable slanted transmission grating according to claim 14, wherein the surfactant is octanol.

16. The switchable slanted transmission grating according to claim 1, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises a mixture of cyanobiphenyls, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal sodium salt.

17. An optical coupling device comprising:

at least one switchable slanted transmission grating according to claim 1; and

at least one voltage source associated with said switchable slanted transmission grating.

18. The optical coupling device according to claim 17, wherein the optical coupling device further comprises at least one transparent substrate.

19. The optical coupling device according to claim 18, wherein the at least one switchable slanted transmission grating is coupled to the at least one transparent substrate.

20. The optical coupling device according to claim 19, wherein the at least one transparent substrate is glass.

21. The optical coupling device according to claim 20, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

22. The optical coupling device according to claim 17, wherein the optical coupling device is a selectively adjustable and reconfigurable one-to-many fan-out optical coupling device.

23. The optical coupling device according to claim 22, wherein the at least one liquid crystal comprises a mixture of cyanobiphenyls.

24. The optical coupling device according to claim 18, wherein the average index of refraction of the at least one switchable slanted transmission grating is similar to the refractive index of the at least one transparent substrate.

25. The optical coupling device according to claim 24, wherein the chain-extending monomer is N-vinyl pyrrolidone.

26. The optical coupling device according to claim 17, wherein the optical coupling device further comprises at least one transparent electrode.

27. The optical coupling device according to claim 26, wherein the coinitiator is N-phenylglycine.

28. The optical coupling device according to claim 18, wherein the at least one switchable slanted transmission grating has a slant angle, θ

s, and the at least one transparent substrate has a critical angle, θ

c, for total internal reflection and wherein 2θ

s>

θ

c.

29. The optical coupling device according to claim 28, wherein the photoinitiator is rose bengal sodium salt.

30. The optical coupling device according to claim 17, wherein the polymer-dispersed liquid crystal material, before exposure, further comprises a surfactant.

31. The optical coupling device according to claim 30, wherein the surfactant is octanol.

32. The optical coupling device according to claim 17, wherein an anti-reflective coating is applied to the at least one switchable slanted transmission grating.

33. The optical coupling device according to claim 17, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises a mixture of cyanobiphenyls, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal sodium salt.

69. A selectively adjustable and reconfigurable one-to-many fan-out optical interconnect, comprising an input optical coupling device and one or more output optical coupling devices in optical contact with a substrate capable of transmitting light therebetween, wherein at least one of said optical coupling devices are according to claim 17.

70. A holographic optical element comprising at least one optical coupling device according to claim 17 in optical contact with a substrate capable of transmitting light.

34. A method for preparing a switchable slanted transmission grating, comprising:

disposing between at least two optically transparent electrode plates, a mixture that comprises, before exposure;

(a) a polymerizable monomer comprising at least one acrylate;

(b) a liquid crystal;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator; and

exposing this mixture to light in an interference pattern.

35. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the polymerizable monomer comprises a mixture of di-, tri-, tetra-, and pentaacrylates.

36. The method for preparing a switchable slanted transmission grating according to claim 35, wherein the polymerizable monomer is at least one acrylate selected from the group consisting of triethyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, and dipentaerythritol pentaacrylate.

37. The method for preparing a switchable slanted transmission grating according to claim 36, wherein the polymerizable monomer comprises a mixture of tri- and pentaacrylates.

38. The method for preparing a switchable slanted transmission grating according to claim 37, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

39. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the at least one liquid crystal is at least one liquid crystal selected from the group consisting of a mixture of cyanobiphenyls, 4′

-n-pentyl-4-cyanobiphenyl, 4′

-n-heptyl-4-cyanobiphenyl, 4′

-octaoxy-4-cyanobiphenyl, 4′

-pentyl-4-cyanoterphenyl, and α

-methoxybenzylidene-4′

-butylaniline.

40. The method for preparing a switchable slanted transmission grating according to claim 39, wherein the at least one liquid crystal comprises a mixture of cyanobiphenyls.

41. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the chain-extending monomer is at least one member selected from the group consisting of N-vinyl pyrrolidone;

N-vinyl pyridine, acrylonitrile, and N-vinyl carbazole.

42. The method for preparing a switchable slanted transmission grating according to claim 41, wherein the chain-extending monomer is N-vinyl pyrrolidone.

43. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the coinitiator is at least one member selected from the group consisting of N-phenylglycine, triethylene amine, triethanolamine, and N,N-dimethyl-2,6-diisopropyl aniline.

44. The method for preparing a switchable slanted transmission grating according to claim 43, wherein the coinitiator is N-phenylglycine.

45. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the photoinitiator is at least one member selected from the group consisting of rose bengal ester, rose bengal sodium salt, eosin, eosin sodium salt, 4,5-diiodosuccinyl fluorescein, camphorquinone, methylene blue, cationic cyanine dyes with trialkylborate anions, and merocyanine dyes derived from spiropyran.

46. The method for preparing a switchable slanted transmission grating according to claim 45, wherein the photoinitiator is rose bengal sodium salt.

47. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the polymer-dispersed liquid crystal material, before exposure, further comprises a surfactant.

48. The method for preparing a switchable slanted transmission grating according to claim 47, wherein the surfactant is octanol.

49. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the light in an interference pattern is obtained from at least two beams of coherent light.

50. The method for preparing a switchable slanted transmission grating according to claim 49, wherein one beam of coherent light arrives at the mixture with a angle of incidence with respect to the second beam.

51. The method for preparing a switchable slanted transmission grating according to claim 34, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises a mixture of cyanobiphenyls, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal sodium salt.

52. A method for preparing an optical coupling device comprising

constructing a switchable slanted transmission grating according to claim 34, and electrically connecting said optically transparent electrodes to a voltage source.

53. The method for preparing an optical coupling device according to claim 52, wherein the optical coupling device further comprises at least one transparent substrate.

54. The method for preparing an optical coupling device according to claim 53, wherein the at least one switchable slanted transmission grating is coupled to the at least one transparent substrate.

55. The method for preparing an optical coupling device according to claim 54, wherein the at least one transparent substrate is glass.

56. The method for preparing an optical coupling device according to claim 55, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

57. The method for preparing an optical coupling device according to claim 52, wherein the optical coupling device is a selectively adjustable and reconfigurable one-to-many fan-out optical coupling device.

58. The method for preparing an optical coupling device according to claim 57, wherein the at least one liquid crystal comprises a mixture of cyanobiphenyls.

59. The method for preparing an optical coupling device according to claim 52, wherein the average index of refraction of the at least one switchable slanted transmission grating is similar to the refractive index of the at least one transparent substrate.

60. The method for preparing an optical coupling device according to claim 59, wherein the chain-extending monomer is N-vinyl pyrrolidone.

61. The method for preparing an optical coupling device according to claim 52, wherein the optical coupling device further comprises at least one transparent electrode.

62. The method for preparing an optical coupling device according to claim 61, wherein the coinitiator is N-phenylglycine.

63. The method for preparing an optical coupling device according to claim 53, wherein the at least one switchable slanted transmission grating has a slant angle, θ

s, and the at least one transparent substrate has a critical angle, θ

c, for total internal reflection and wherein 2θ

s>

θ

c.

64. The method for preparing an optical coupling device according to claim 63, wherein the photoinitiator is rose bengal sodium salt.

65. The method for preparing an optical coupling device according to claim 52, wherein the polymer-dispersed liquid crystal material, before exposure, further comprises a surfactant.

66. The method for preparing an optical coupling device according to claim 65, wherein the surfactant is octanol.

67. The method for preparing an optical coupling device according to claim 52, wherein an anti-reflective coating is applied to the at least one switchable slanted transmission grating.

68. The method for preparing an optical coupling device according to claim 52, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises a mixture of cyanobiphenyls, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal sodium salt.