Liquid crystal variable optical attenuator

• US 6,897,917 B2
• Filed: 03/03/2003
• Issued: 05/24/2005
• Est. Priority Date: 02/21/2003
• Status: Expired due to Term

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: SpectraSwitch, Inc.
• Inventors: Cavanaugh, Shanti A., Young, Mark E., Molinari, Louis J., Austin, Lindsay W.
• Primary Examiner(s): Dudek, James A.
• Application Number:
  US10/379,384
• Publication Number:
  US 20040174473A1
• Time in Patent Office: 813 Days
• Field of Search: 349/96, 349/196, 349/197, 349/198, 359/486, 359/487
• US Class Current: 349/96
• CPC Class Codes: G02F 1/093 used as non-reciprocal devices, e.g. optical isolators, circulators G02F1/0955 takes precedence
• CPC Class Codes: G02F 1/1326 Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides
• CPC Class Codes: G02F 1/133382 Heating or cooling of liquid crystal cells other than for activation, e.g. circuits or arrangements for temperature control, stabilisation or uniform distribution over the cell
• CPC Class Codes: G02F 1/133521 Interference filters
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/13355 Polarising beam splitters [PBS]
• CPC Class Codes: G02F 1/1339 Gaskets; Spacers; Sealing of cells
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 2201/305 diffraction grating
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/06 Polarisation independent
• CPC Class Codes: G02F 2203/12 spatial light modulator

Abstract

A twisted nematic liquid crystal variable optical attenuator is presented with one substrate that includes a integrated subwavelength nanostructured polarizer. The device may incorporate an integrated isolator whereby a substrate of the liquid crystal sandwich is formed from doped garnet to comprise a faraday rotator etched with a subwavelenth optical nanostructured polarizing grating and enabling the substrate to function as an isolator. The liquid crystal variable optical attenuator may include a deposited metal gasket moisture barrier bonding the opposing top and bottom substrates each having a spacer layer to accurately control cell gap thickness. The liquid crystal variable optical attenuator may also include an integrated thermal sensor and heater deposition layer sandwiched between or deposited on at least one or both opposing substrates.

Claims

1. A variable optical attenuator, comprising:

a first substrate having a top surface etched with a subwavelength grating polarizer and a bottom surface having electrode and alignment layers,

a second substrate having a bottom surface etched with a second sub wavelength optical grating polarizer and a top surface having a second electrode and alignment layers, said second polarizer having an optical axis orthogonal to the polarizer on the first substrate, said top surface of second substrate placed in opposition to the bottom surface of first substrate,

liquid crystals coupled between the first and second substrates,

wherein an optical signal polarized with the same optical axis as the second polarizer is rotated as it passes through the liquid crystal and may be variably attenuated by the second polarizer with the application of voltage across the electrode layers.

2. The variable optical attuenator of claim 1, further including a spacer layer coupled between the first and second substrates and a metal gasket layer bonded to the first and second substrates.

3. The variable optical attuenator of claim 2, further including an active thermal element disposed between the first and second substrates.

4. The variable optical attuenator claim 2, wherein the spacer layer contains one or more materials selected from the group consisting of silicon dioxide, aluminum oxide, silicon nitride, silicon monoxide.

5. The variable optical attuenator of claim 2, wherein the metal gasket layer includes one or more materials selected from the group consisting of indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium and lead.

6. The variable optical attuenator of claim 2, wherein both substrates are glass.

7. The variable optical attenuator of claim 2, wherein the spacer layer and metal gasket layer are deposited thin film.

8. The variable optical attenuator of claim 3, wherein the active thermal element is deposited onto the first and second substrates.

9. The variable optical attenuator of claim 3, wherein the active thermal element is disposed substantially around the perimeter of the liquid crystal cell.

10. The variable optical attenuator of claim 3, wherein the active thermal element is arranged in a serpentine pattern.

11. The variable optical attenuator of claim 3, wherein the active thermal element provides heating and temperature sensing capability.

12. The variable optical attenuator of claim 3, wherein the active thermal element is comprised of chrome-platinum.

13. The variable optical attenuator of claim 3, further including at least one VIA formed between the metal spacer layer and first or second electrodes.

14. The variable optical attenuator of claim 3, further including at least one VIA formed between the active thermal element and the metal spacer layer.

15. The variable optical attenuator of claim 3, wherein the active thermal element has electrodes that provide a resistance value used to determine temperature of the variable optical attenuator.

16. The variable optical attenuator of claim 15, further including a microcontroller and switch coupled to the active thermal element such that the state of the switch controls routes resistance values from the active thermal element to the microcontroller and voltage signals from the microcontroller to the active thermal element.

17. The variable optical attenuator of claim 16, wherein a VIA formed by a layer of metal gasket material connects the thermal element across the first and second substrates.

18. A variable optical attenuator, comprising:

a first substrate having a top surface etched with a subwavelength grating polarizer and a bottom surface having a first electrode layer and a first alignment layer,

a second substrate comprising a top surface having a second electrode layer, and a second alignment layer anchored in an orthogonal orientation to the first alignment layer, said second substrate placed in opposition to the bottom surface of first substrate,

liquid crystals coupled between the first and second substrates,

a spacer layer coupled between the first and second substrates,

a metal gasket layer bonded to the first and second substrates,

wherein an optical signal transmitted through the second substrate may have its polarization rotated as it passes throught the liquid crystals and variably attenated at the polarizer on the first substrate with the application of voltage.

19. A variable optical attenuator, comprising:

a first substrate made from material suitable to enable the substrate to perform as a Faraday rotator, said first substrate having top and bottom surfaces etched with a subwavelength grating polarizers whereby the top surface polarizer is 45 degrees offset from the bottom polarizer to enable the substrate to perform as an isolator, said first substrate further comprising on the bottom surface a first electrode layer, and a first alignment layer,

a second substrate comprising a top surface having a second electrode layer, and a second alignment layer that is anchored in an orthogonal orientation to the first alignment layer, said second substrate placed in opposition to the bottom surface of first substrate,

liquid crystals coupled between the first and second substrates,

wherein an optical signal transmitted through the second substrate may have its polarization rotated as it passes through the liquid crystals, variably attenuated by the bottom polarizer on the first substrate with the application of voltage on the electrode layers, and isolated by the isolator formed from the first substrate.

20. The variable optical attuenator of claim 19, further including a spacer layer coupled between the first and second substrates and a metal gasket layer bonded to the first and second substrates.

21. The variable optical attuenator of claim 20, further including an active thermal element disposed between the first and second substrates.

22. The variable optical attuenator claim 20, wherein the spacer layer contains one or more materials selected from the group consisting of silicon dioxide, aluminum oxide, silicon nitride, silicon monoxide.

23. The variable optical attuenator of claim 20, wherein the metal gasket layer includes one or more materials selected from the group consisting of indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium and lead.

24. The variable optical attuenator of claim 20, wherein both substrates are glass.

25. The variable optical attunator of claim 20, wherein the spacer layer and metal gasket layer are deposited thin film.

26. The variable optical attenuator of claim 21, wherein the active thermal element is deposited onto the first and second substrates.

27. The variable optical attunator of claim 21, wherein the active thermal element is disposed substantially around the perimeter of the liquid crystal cell.

28. The variable optical attunator of claim 21, wherein the active thermal element is arranged in a serpentine pattern.

29. The variable optical attunator of claim 21, wherein the active thermal element provides heating and temperature sensing capability.

30. The variable optical attunator of claim 21, wherein the active thermal element is comprised of chrome-platinum.

31. The variable optical attunator of claim 21, further including at least one VIA formed between the metal spacer layer and first or second electrodes.

32. The variable optical attunator of claim 21, further including at least one VIA formed between the active thermal element and the metal spacer layer.

33. The variable optical attenuator of claim 21, wherein the active thermal element has electrodes that provide a resistance value used to determine temperature of the variable optical attunator.

34. The variable optical attenuator of claim 33, further including a microcontroller and switch coupled to the active thermal element such that the state of the switch controls routes resistance values from the active thermal element to the microcontroller and voltage signals from the microcontroller to the active thermal element.

35. The variable optical attenuator of claim 34, wherein a VIA formed by a layer of metal gasket material connects the thermal element across the first and second substrates.

36. A variable optical attenuator, comprising:

a first substrate etched with a subwavelength grating polarizer and having a first electrode layer, and a first alignment layer,

a second substrate made from material suitable to enable the substrate to perform as a Faraday rotator, said second substrate having top and bottom surfaces both etched with subwavelength grating polarizers whereby the top surface polarizer is 45 degrees offset from the bottom surface polarizer to enable the substrate to perform as an isolator, said second substrate further comprising on the top surface a second electrode layer, and a second alignment layer, said second aligment layer achnored in a substantially orthogonal orientation to the first alignment layer on the first substrate, said top surface of the second substrate placed in opposition to the bottom surface of first substrate,

liquid crystals coupled between the first and second substrates,

wherein an optical signal transmitted through the second substrate may be isolated by the second substrate, rotated as it passes through the liquid crystals, variably attenuated by the polarizer on the first substrate with the application of voltage on the electrode layers.

37. The variable optical attuenator of claim 36, further including a spacer layer coupled between the first and second substrates and a metal gasket layer bonded to the first and second substrates.

38. The variable optical attuenator of claim 37, further including an active thermal element disposed between the first and second substrates.

39. The variable optical attuenator claim 37, wherein the spacer layer contains one or more materials selected from the group consisting of silicon dioxide, aluminum oxide, silicon nitride, silicon monoxide.

40. The variable optical attuenator of claim 37, wherein the metal gasket layer includes one or more materials selected from the group consisting of indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium and lead.

41. The variable optical attuenator of claim 37, wherein both substrates are glass.

42. The variable optical attunator of claim 37, wherein the spacer layer and metal gasket layer are deposited thin film.

43. The variable optical attenuator of claim 38, wherein the active thermal element is deposited onto the first and second substrates.

44. The variable optical attunator of claim 38, wherein the active thermal element is disposed substantially around the perimeter of the liquid crystal cell.

45. The variable optical attunator of claim 38, wherein the active thermal element is arranged in a serpentine pattern.

46. The variable optical attunator of claim 38, wherein the active thermal element provides heating and temperature sensing capability.

47. The variable optical attunator of claim 38, wherein the active thermal element is comprised of chrome-platinum.

48. The variable optical attunator of claim 38, further including at least one VIA formed between the metal spacer layer and first or second electrodes.

49. The variable optical attunator of claim 38, further including at least one VIA formed between the active thermal element and the metal spacer layer.

50. The variable optical attenuator of claim 38, wherein the active thermal element has electrodes that provide a resistance value used to determine temperature of the variable optical attunator.

51. The variable optical attenuator of claim 50, further including a microcontroller and switch coupled to the active thermal element such that the state of the switch controls routes resistance values from the active thermal element to the microcontroller and voltage signals from the microcontroller to the active thermal element.

52. The variable optical attenuator of claim 51, wherein a VIA formed by a layer of metal gasket material connects the thermal element across the first and second substrates.