Optical switching device using holographic polymer dispersed liquid crystals

• US 20050259217A1
• Filed: 05/20/2004
• Published: 11/24/2005
• Est. Priority Date: 05/20/2004
• Status: Active Grant

• Current Assignee: Alps Electric North America Incorporated (Alps Alpine Co., Ltd.)
• Original Assignee: Alps Electric North America Incorporated (Alps Alpine Co., Ltd.)
• Inventors: Aihara, Masami, Tang, Suning, Tang, Yuanji, Lin, Jibing
• Granted Patent: US 7,301,601 B2
• Time in Patent Office: Days
• US Class Current: 349/196
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

A thin holographic optical switch used in a liquid crystal display device contains opposing transparent substrates transparent electrodes between the substrates and a diffraction grating between the electrodes. The diffraction grating contains regions of transparent polymerized photopolymers and cholesteric liquid crystal micro-droplets. Refractive indexes of the photopolymers and liquid crystal are substantially the same when the electrodes have the same potential. The holographic optical switch transmits broadband LED light when the potential difference between the electrodes is zero and is polarization independent. The holographic optical switch diffracts broadband LED light when the potential difference between the electrodes is non-zero and is polarization independent.

Claims

1. An optical switch comprising:

opposing substrates;

electrodes disposed between the substrates; and

a diffraction grating disposed between the electrodes, the diffraction grating containing regions of a polymerized photopolymer having a refractive index and liquid crystal aggregates having an effective refractive index that is substantially equal to the refractive index of the photopolymer when the electrodes have the same potential.

2. The optical switch of claim 1, wherein the effective refractive index of the liquid crystal aggregates is tunable by applying a voltage between the opposing substrates.

3. The optical switch of claim 1, wherein the grating is substantially polarization independent.

4. The optical switch of claim 1, wherein the grating is designed to transmit light with a wavelength of about 190 nm to about 2 μ

m.

5. The optical switch of claim 1, wherein the grating is tunable to diffract light with a wavelength of about 190 nm to about 2 μ

m by applying an electrical field between the electrodes.

6. The optical switch of claim 1, wherein the grating is designed to switch light from a light emitting diode (LED).

7. The optical switch of claim 6, wherein the LED is a blue LED.

8. The optical switch of claim 1, further comprising phosphor disposed on one or more surfaces of the optical switch, or inside the optical switch, to absorb light impinging thereon and emit light of at least one other color.

9. The optical switch of claim 1, wherein the photopolymer comprises one or more monomers, oligomers, or photoinitiators.

10. The optical switch of claim 9, wherein the photopolymer further comprises one or more of surfactants, adhesion promoters or stablizers.

11. The optical switch of claim 1, wherein the polymerized photopolymer has a relatively high index of refraction sufficient to match the effective refractive index of the liquid crystal aggregates when the electrodes have the same potential.

12. The optical switch of claim 1, wherein the polymerized photopolymer has a refractive index higher than about 1.55.

13. The optical switch of claim 1, wherein the liquid crystal aggregates comprise at least one cholesteric liquid crystal.

14. The optical switch of claim 13, wherein the cholestric liquid crystals comprise one or more of:

BL 112, BL 118, or BL 126.

15. The optical switch of claim 1, wherein a refractive index modulation of the liquid crystal aggregates is substantially the same for both the p and s polarizations of light impinging on the diffraction grating.

16. The optical switch of claim 1, wherein the liquid crystal aggregates comprise at least one chiral dopant.

17. The optical switch of claim 16, wherein the chiral dopant comprises one or more of:

Merck C15, CB15, ZLI-811, ZLI-3786, ZLI-4571, and ZLI-4572.

18. The optical switch of claim 1, wherein a single layer containing the polymerized photopolymers and liquid crystal aggregates is present in the grating.

19. The optical switch of claim 1, wherein a plurality of layers containing the polymerized photopolymers and liquid crystal aggregates is present in the grating.

20. The optical switch of claim 1, wherein a weight percentage of the liquid crystal aggregates with respect to a total weight of the liquid crystal aggregates and polymerized photopolymers is 35 to 75%.

21. The optical switch of claim 20, wherein the weight percentage is 45 to 60%.

22. The optical switch of claim 11, wherein the photopolymer comprises one or more of monomers or oligomers that have a high refractive index.

23. The optical switch of claim 22, wherein the one or more of monomers and oligomers comprise one or more of:

sulfur elements, bromine elements, or bisphenol A derivatives.

24. The optical switch of claim 13, wherein the photopolymer comprises one or more of monomers or oligomers that have a high refractive index.

25. The optical switch of claim 14, wherein the one or more of monomers and oligomers comprise one or more of:

sulfur elements, bromine elements, or bisphenol A derivatives.

26. The optical switch of claim 13, wherein the liquid crystal aggregates are formed from at least two different cholesteric liquid crystals of different weight percentages.

27. An optical switch comprising:

opposing substrates;

electrodes disposed between the substrates; and

a diffraction grating disposed between the electrodes, the diffraction grating containing regions of a polymerized photopolymer having a refractive index and liquid crystal aggregates having an effective refractive index that is substantially equal to the refractive index of the photopolymer when the electrodes have the same potential, and a refractive index modulation of the liquid crystal aggregates is substantially the same for both the p and s polarizations of light impinging on the diffraction grating.

28. The optical switch of claim 27, wherein the effective refractive index of the liquid crystal aggregates is tunable by applying a voltage between the opposing substrates.

29. The optical switch of claim 27, wherein the grating is designed to transmit light with a wavelength of about 190 nm to about 2 μ

m.

30. The optical switch of claim 27, wherein the grating is tunable to diffract light with a wavelength of about 190 nm to about 2 μ

m by applying an electrical field between the electrodes.

31. The optical switch of claim 27, wherein the polymerized photopolymer has a relatively high index of refraction sufficient to match the effective refractive index of the liquid crystal aggregates when the electrodes have the same potential.

32. The optical switch of claim 27, wherein the polymerized photopolymer has a refractive index higher than 1.55.

33. The optical switch of claim 27, wherein the liquid crystal aggregates comprise at least one cholesteric liquid crystal.

34. The optical switch of claim 27, wherein the liquid crystal aggregates comprise at least one chiral dopant.

35. The optical switch of claim 27, wherein a single layer containing the polymerized photopolymers and liquid crystal aggregates is present in the grating.

36. The optical switch of claim 27, wherein a plurality of layers containing the polymerized photopolymers and liquid crystal aggregates is present in the grating.

37. The optical switch of claim 27, wherein a weight percentage of the liquid crystal aggregates with respect to a total weight of the liquid crystal aggregates and polymerized photopolymers is 35 to 75%.

38. A method of manufacturing optical switch devices using a holographic polymer dispersed liquid crystal (HPDLC), the method comprising:

blending liquid crystals and photopolymers to form a mixture;

filling a cavity formed by substrates with the mixture; and

forming, from the mixture, periodical alternating regions of liquid crystal aggregates and polymerized photopolymers in which an effective refractive index of the liquid crystal aggregates is substantially equal to a refractive index of the matrix when no voltage is applied to the polymerized photopolymers and liquid crystal aggregates.

39. The method of claim 38, the forming comprising exposing the filled cavity to radiation.

40. The method of claim 39, wherein the radiation comprises photolithiography radiation.

41. The method of claim 40, the exposing comprising exposing the filled cavity to the radiation through a phase mask.

42. The method of claim 39, the exposing comprising flooding the filled cavity with uniform radiation to cure the polymers after the formation of the periodical alternating regions.

43. The method of claim 38, the forming comprising exposing the filled cavity to an interference pattern of coherent laser beams.

44. The method of claim 38, further comprising joining the substrates to form the cavity prior to filling the cavity with the mixture.

45. The method of claim 38, further comprising creating a substantially homogeneous mixture before filling the cavity with the mixture.

46. The method of claim 39, the exposing comprising splitting a single beam of radiation to form intersecting radiation beams.

47. The method of claim 46, further comprising splitting the single beam into two substantially identical radiation beams.

48. The method of claim 46, further comprising expanding the single radiation beam.

49. The method of claim 38, further comprising testing the HPDLC by applying a light source to determine whether light from the light source is transmitted through the HPDLC when no voltage is applied to the HPDLC.

50. The method of claim 49, further comprising testing the HPDLC by determining a voltage at which a maximum amount of light is diffracted by the HPDLC.

51. The method of claim 38, further comprising forming a matrix containing the liquid crystal aggregates and polymerized photopolymers in which s and p polarizations of light incident on the HPDLC are affected in substantially the same manner independent of a voltage applied to the HPDLC.

52. The method of claim 38, further comprising disposing phosphor on one or more surfaces of the optical switch, or inside the optical switch, to absorb light impinging thereon and emit light of at least one other color.