Fabry-perot interferometer array

• US 20080049228A1
• Filed: 08/28/2006
• Published: 02/28/2008
• Est. Priority Date: 08/28/2006
• Status: Abandoned Application

• Current Assignee: Novaspectra Incorporated
• Original Assignee: Novaspectra Incorporated
• Inventors: Chan, William S.
• Application Number:
  US11/510,815
• Publication Number:
  US 20080049228A1
• Time in Patent Office: Days
• US Class Current: 356/454
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G01J 3/2823 Imaging spectrometer
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems

Abstract

This disclosure describes a fabry-perot interferometer array and methods of using it for gas sensing, hyper-spectral imaging, scene projection and optical communications. Processed on a silicon, silicon-on-sapphire, or other substrates with integrated circuits, the array may be sized from one pixel to multi-mega pixels and made to cover the entire ultraviolet (UV) to long wave infrared (LWIR) spectrum, allowing it to be used in many applications. In preferred embodiments, each pixel of the array is a fabry-perot interferometer cavity, sandwiched between two parallel mirrors, whose spacing is changed by moving one of the mirrors relative to the other with a voltage applied across the cavity, tuning it to transmit a waveband with a bandwidth and a central wavelength determined by the mirror reflectivity and the cavity spacing, respectively. Thus, an array of different wavebands may be electrically tuned to transmit from the array.

Claims

1. An array of micro fabry-perot cavities for tuning radiation wavebands, wherein said array comprises at least one cavity in a first dimension and at least one cavity in at least one other dimension.

2. An array as in claim 1 wherein said first and at least one of said other dimensions are orthogonal to one another.

3. An array as in claim 1 wherein said first and other dimensions are at some angle other than orthogonal to one another.

4. An array as in claim 1 wherein said array further comprises circuits to tune the cavities and operate the array.

5. An array as in claim 1 wherein each cavity of the array comprises:

a top mirror comprising at least one top mirror segment and

a bottom mirror comprising at least one bottom mirror segment,

wherein said top and bottom mirror sandwich an air-gap cavity with a cavity spacing.

6. An array as in claim 5 wherein said top mirror comprises a plurality of mirror segments.

7. An array as in claim 5 wherein said bottom mirror comprises a plurality of mirror segments.

8. An array as in claim 5 wherein said top mirror is suspended by at least one support structure.

9. An array as in claim 8 wherein said at least one support structure is a cantilever.

10. An array as in claim 8 wherein said cantilever is parallel to one side of the top mirror.

11. An array as in claim 8 wherein some portion of said cantilever is parallel to two neighboring sides of the top mirror.

12. An array as in claim 8 wherein said support structure is firmly anchored to a substrate via at least one anchor.

13. An array as in claim 8 wherein said top mirror is moved via said support structure(s) relative to a bottom mirror.

14. An array as in claim 13 wherein said movement of said top mirror results from the flexing of said support structure(s).

15. An array as in claim 13 wherein said movement of at least one segment of said top mirror towards or away from at least a segment of said bottom mirror results from an electrostatic force created by applying a voltage across the air-gap cavity.

16. An array as in claim 5 wherein a voltage applied to at least one bottom mirror segment causes at least one top mirror segment to become substantially parallel with the bottom mirror.

17. An array as in claim 5 wherein the movement of at least one top mirror segment corrects for non-parallelism between said top mirror and said bottom mirror.

18. An array as in claim 5 wherein a voltage applied to at least one bottom mirror segment changes the distance from the top mirror to the bottom mirror, changing the cavity air-gap to a distance corresponding to at least one spectral waveband.

19. An array as in claim 5 wherein the movement of said at least one top mirror segment tunes the cavity to transmit at least one spectral region.

20. An array as in claim 5 wherein said cavity spacing is preset in order to generate at least one spectral region.

21. An array as in claim 5 where the cavity spacing is preset to generate at least one specific spectral region via altering the height of at least one of the support structure'"'"'s at least one anchor.

22. An array as in claim 5 where a cavity can be tuned from a first waveband to a second waveband in less than 1 microsecond.

23. An array as in claim 5 where the frame rate of the array is up to 1,000 Hz.

24. An array as in claim 5 wherein each of said mirrors comprises at least one bilayer.

25. An array as in claim 5 wherein each of said mirrors comprises a plurality of bilayers.

26. An array as in claim 25 wherein each of said bilayers comprises a dielectric film of high refractive index and a dielectric film of low refractive index, producing a specific reflectivity in the two mirrors.

27. An array as in claim 26 wherein said dielectric film of high refractive index closest to and on either side of the air-gap cavity comprises a doped medium so that the film is more electrically conducting than the film of low refractive index, producing a uniform distribution of an applied voltage over the film.

28. An apparatus for gas sensing comprising at least one micro fabry-perot interferometer element, at least one detector element, an infrared source, a collimating lens, a gas path length, a cavity controller, a detector controller, and a control processor, wherein gas of a specific type located between the infrared source and said at least one micro fabry-perot interferometer element can be detected.

29. An apparatus as in claim 28 comprising an array of micro fabry-perot interferometer elements, a multi-element infrared detector array, an imaging lens, an infrared detector array controller, and a micro fabry-perot interferometer (MFPI) array controller, wherein a plurality of gas types located between the infrared source and said micro fabry-perot interferometer array can be detected simultaneously.

30. An apparatus as in claim 29, wherein all cavities of said MFPI array are tuned to a waveband absorbed by a gas in a gas cloud, to obtain a spatial distribution of the gas.

31. An apparatus as in claim 29, wherein all cavities of said MFPI array are tuned to different wavebands absorbed by different gases sequentially, to obtain a sequence of spatial distributions of different gases in the gas cloud.

32. An apparatus as in claim 29, wherein all cavities of said MFPI array are tuned to a different waveband absorbed by a different gas, to obtain a single distribution of different gases in the gas cloud.

33. An apparatus as in claim 29, wherein all cavities of said MFPI array are tuned to a waveband absorbed by a gas product resulting from a chemical reaction, to obtain a single distribution of different gas products.

34. An apparatus as in claim 29, wherein all cavities of said MFPI array are tuned to variably, to obtain spectral, spatial, temporal, chemical reaction and concentration distributions of the gas cloud nearly simultaneously.

35. An apparatus as in claim 29, further comprising:

A. means of tuning all cavities of the interferometer array to a waveband absorbed by a gas in a gas cloud, to obtain a spatial distribution of the gas;

B. means for tuning all cavities of the interferometer array to different wavebands absorbed by different gases sequentially, to obtain a sequence of spatial distributions of different gases in the gas cloud;

C. means for tuning each cavity of the interferometer array to a different waveband absorbed by a different gas, to obtain a single distribution of different gases in the gas cloud;

D. means for tuning each cavity of the interferometer array to a waveband absorbed by a gas product resulted from a chemical reaction, to obtain a single distribution of different gas products; and

E. means for tuning said cavities of the interferometer array variably, to obtain spectral, spatial, temporal, chemical, reaction and concentration distributions of the gas cloud nearly simultaneously.

36. A method for gas sensing comprising:

A. collimating an infrared beam through a gas onto an interferometer element;

B. tuning the cavity of the interferometer element a first time to transmit a waveband absorbed by the gas;

C. tuning said cavity a second time to transmit another waveband not absorbed by the gas as a reference;

D. sensing the absorbed waveband and the non-absorbed waveband sequentially with a detector element; and

E. computing a concentration of the gas with a ratio of a signal due to the absorbed waveband to a signal due to the non-absorbed waveband, according to;

CG=A.Log(Q),

 

where CG is said concentration, Q is said ratio, and A is a constant obtained by calibration with a known concentration of the gas.

37. A method for gas sensing as in claim 36, further comprising a method for computing a low concentration if said low concentration is less than one part per million of said gas with said ratio, according to:

CG=AO+A1.Log(Q)+A2.[Log(Q)]²,

where CG is said low concentration, Q is said ratio, and AO, A1 and A2 are constants obtained by calibration with at least three known concentrations of said gas before sensing.

38. An apparatus for hyper-spectral imaging comprising a micro fabry-perot interferometer array, an infrared detector array, an imaging lens, an infrared-detector-array controller, and a micro fabry-perot interferometer (MFPI) array controller, wherein data collected by said array provides a multi-spectral, multi-spatial, and/or temporal image of targets and background.

39. An apparatus as in claim 38, wherein all cavities of said MFPI array are tuned to a specific waveband, to obtain a spatial image at said waveband.

40. An apparatus as in claim 38, wherein all cavities of said MFPI array are tuned to one waveband at different times, to obtain a sequence of spatial images at said waveband.

41. An apparatus as in claim 38, wherein all cavities of said MFPI array are tuned to different wavebands sequentially, to obtain a sequence of spatial images of said different wavebands.

42. An apparatus as in claim 38, wherein each cavity of said MFPI array is tuned to different wavebands, to obtain a single spatial image of different wavebands

43. An apparatus as in claim 38, wherein certain segments of said MFPI array are tuned to different wavebands to correspond to different targets, to obtain images of targets enhanced against background

44. An apparatus as in claim 38, wherein all cavities of said MFPI array are variably tuned to obtain spectral, spatial, and temporal images nearly simultaneously of targets and background.

45. An apparatus as in claim 38, further comprising:

A. means for tuning all cavities of the interferometer array to a specific waveband, to obtain a spatial image at said waveband;

B. means for tuning all cavities of the interferometer array to one waveband at different times, to obtain a sequence of spatial images of said waveband;

C. means for tuning all cavities of the interferometer array to different wavebands sequentially, to obtain a sequence of spatial images of said different wavebands;

D. means for tuning each cavity of the interferometer array to a different waveband, to obtain a single spatial image of different wavebands;

E. means for tuning certain segments of the interferometer array to different wavebands to correspond to different targets, to obtain images of targets enhanced against background; and

F. means for tuning cavities of the interferometer array variably, to obtain spectral, spatial, and temporal images nearly simultaneously of targets and background.

46. An apparatus for projecting scenes, comprising a micro fabry-perot interferometer (MFPI) array, a laser source, a collimator, a focusing lens, a laser controller, and an MFPI array controller, wherein the cavities of said MFPI array are independently tuned to generate at least one scene.

47. An apparatus as in claim 46 wherein said MFPI array generates a sequence of scenes.

48. An apparatus as in claim 46 wherein said scene(s) is projected onto a sensor under test.

49. An apparatus as in claim 46 wherein a short-wave infrared MFPI array is used to project short-wave infrared scenes.

50. An apparatus as in claim 46 wherein a mid-wave infrared MFPI array is used to project mid-wave infrared scenes.

51. An apparatus as in claim 46 wherein a long-wave infrared MFPI array is used to project long-wave infrared scenes.

52. An apparatus as in claim 46 wherein a visible frequency MFPI array is used to project visible scenes.

53. An apparatus as in claim 46 wherein an ultraviolet MFPI array is used to project ultraviolet scenes.

54. An apparatus as in claim 46 wherein at least two MFPI arrays and matched laser sources simultaneously project a scene comprising at least two different wavebands.

55. A method of testing a sensor using a micro fabry-perot interferometer (MFPI) array comprising:

A. illuminating at least one MFPI array with a laser source;

B. tuning at least some of the cavities of the MFPI array to at least one waveband producing at least one scene;

C. projecting the scene(s) onto the sensor under test; and

D. recording response of the sensor under test using a sensor controller.

56. An apparatus for optical communications comprising at least one micro fabry-perot interferometer (MFPI) array, at least one laser source, a projector lens, a laser controller, and an MFPI array controller, wherein at least one optical channel is coded with data for transmission through free space to at least one distant optical receiver.

57. An apparatus as in claim 56, wherein a plurality of optical channels are simultaneously coded with data for transmission.

58. An apparatus as in claim 56, wherein said at least one MFPI array and laser source transmit on short-wave infrared wavebands.

59. An apparatus as in claim 56, wherein said at least one MFPI array and laser source transmit on mid-wave infrared wavebands.

60. An apparatus as in claim 56, wherein said at least one MFPI array and laser source transmit on long-wave infrared wavebands.

61. An apparatus as in claim 56, wherein said at least one MFPI array and laser source transmit on visible wavebands.

62. An apparatus as in claim 56, wherein said at least one MFPI array and laser source transmit on ultraviolet wavebands.

63. An apparatus as in claim 56 wherein at least two MFPI arrays and laser sources are used to simultaneously transmit data on at least two separate wavebands.

64. An apparatus as in claim 56, wherein said optical communications provide for at least one microchip-to-microchip optical interconnect.

65. A method for transmitting data via optical communications comprising:

A. illuminating at least one micro fabry-perot interferometer (MFPI) array with a laser source;

B. tuning the cavities of the MFPI array to different wavebands producing different optical channels;

C. coding the optical channels with data for communication; and

D. projecting the optical channels through free space onto a distant receiver.

66. A method for fabricating a micro fabry-perot interferometer array, comprising:

A. obtaining a substrate of a specific material quality;

B. fabricating a set of integrated circuits for the array onto said substrate, using standard micro-electronic fabrication techniques;

C. fabricating the bottom mirrors above the integrated circuits;

D. creating a sacrificial layer above the bottom mirrors;

E. creating a supporting structure to be used to support the top mirrors within the sacrificial layer;

F. fabricating the top mirrors above the support structures; and

G. removing the sacrificial layer leaving behind said support structures;

thus, forming the array.

67. A method as in claim 66 wherein said substrate is Silicon.

68. A method as in claim 66 wherein said substrate is Silicon-on-Sapphire

69. A method as in claim 66 wherein said substrate is diamond

70. A method as in claim 66 wherein said substrate is glass.

71. A method as in claim 66 wherein said support structure is a cantilever.