Optical Spectroscopy with Overlapping Images

• US 20060274308A1
• Filed: 06/05/2006
• Published: 12/07/2006
• Est. Priority Date: 06/06/2005
• Status: Active Grant

• Current Assignee: Duke University
• Original Assignee: Duke University
• Inventors: Brady, David J., Gehm, Michael E., Cull, Evan C.
• Granted Patent: US 7,283,232 B2
• Time in Patent Office: Days
• US Class Current: 356/326
• CPC Class Codes: G01J 2003/1217 Indexed discrete filters or choppers
• CPC Class Codes: G01J 2003/1239 and separate detectors
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/2823 Imaging spectrometer
• CPC Class Codes: G01J 3/36 Investigating two or more bands of a spectrum by separate detectors

Abstract

An optical spectrometer distinguishes ambiguity between different wavelength constituent components present in incident light. A spatial filter in the spectrometer spatially filters the incident light. A dispersion system receives the spatially filtered light and disperses images of the spatial filter in a wavelength dependent fashion such that two or more wavelength-specific images at least partially overlap at a detector system. The detector system comprises a detector array and processor that detects and processes the dispersed light to remove ambiguity between one or more of the overlapping images. The detector array may detect coded aperture images associated with a coded aperture spatial filter defined by a coded aperture function, and the processor may process the detector array output signals using an analysis function that complements the coded aperture function. The detector system may filter the spatial filter images and electronically process the resulting detector array output signals.

Claims

1. An optical spectrometer comprising:

a spatial filter configured to spatially filter incident light;

a detector system comprising a two-dimensional detector array operatively connected to a processor;

a dispersion system disposed optically between the spatial filter and the detector system, the dispersion system configured to disperse images of the spatial filter in a wavelength dependent fashion onto the detector system;

wherein a first set of images corresponding to a first spectral subset of wavelengths are dispersed in a first direction, wherein a second set of images corresponding to a second spectral subset of wavelengths are dispersed in the first direction, and wherein at least one of the images in the first set at least partially overlap, at the detector system, at least one of the images in the second set in a second direction different from the first direction; and

wherein the detector system is configured to process detected images to distinguish signals associated with an image in the first set from signals associated with an overlapping image in the second set.

2. The spectrometer of claim 1 wherein the dispersion system is configured to two-dimensionally disperse images of the spatial filter in a wavelength dependent fashion onto the detector system.

3. The spectrometer of claim 2 wherein the dispersion system is configured to two-dimensionally disperse images of the spatial filter such that the first and second sets of images only partially overlap in the second direction.

4. The spectrometer of claim 2 wherein the spatial filter comprises a coded aperture configured to spatially filter incident light according to a coded aperture function.

5. The spectrometer of claim 4 wherein the processor is configured to process the detected images by applying an analysis function to one or more detector output signals corresponding to one or more images, wherein the analysis function complements the coded aperture function.

6. The spectrometer of claim 4 wherein the coded aperture is configured to create linearly independent spatial patterns in each image.

7. The spectrometer of claim 4 wherein the coded aperture function comprises a function defined by independent column codes.

8. The spectrometer of claim 4 wherein the coded aperture comprises a static transmission mask.

9. The spectrometer of claim 1 wherein the detector system filters the images in the first set according to a first passband corresponding to the first spectral subset, and wherein the detector system filters the images in the second set according to a second passband corresponding to the second spectral subset.

10. The spectrometer of claim 9 wherein the detector system comprises first and second filters disposed proximate the detector array, wherein the first filter is configured to optically filter the images in the first set according to the first passband, and wherein the second filter is configured to optically filter the images in the second set according to the second passband.

11. The spectrometer of claim 10 wherein the first filter is integrated with each detector element in a first set of detector array elements, and wherein the second filter is integrated with each detector element in a second set of detector array elements.

12. The spectrometer of claim 10 wherein the first filter is disposed optically upstream from the detector array and aligned with a first region of the detector array associated with the first spectral subset, and wherein the second filter is disposed optically upstream from the detector array and aligned with a second region of the detector array associated with the second spectral subset.

13. The spectrometer of claim 9 wherein the processor is configured to generate a first spectrum output based on detector output signals associated with the first filtered images, and wherein the processor is configured to generate a second spectrum output based on detector output signals associated with the second filtered images.

14. The spectrometer of claim 13 wherein the processor is configured to generate a combined spectrum output based on the first and second spectrum outputs.

15. The spectrometer of claim 14 wherein the first and second passbands partially overlap, and wherein the processor is configured to correct for the overlap between the first and second passbands before generating the combined spectrum output.

16. The spectrometer of claim 13 wherein the processor is configured to generate a plurality of spectral estimates for two or more wavelengths in the first and second spectral subsets based on the corresponding detector output signals, wherein the processor is configured to average the plurality of spectral estimates for two or more wavelengths in the first and second spectral subsets to generate wavelength-specific spectral estimates, and wherein the processor is configured to generate the first and second spectrum outputs based on the wavelength-specific spectral estimates.

17. The spectrometer of claim 9 wherein the images in the first set fully overlap the images in the second set.

18. The spectrometer of claim 9 wherein the detector system comprises a time varying filter configured to optically filter the images in the first set according to the first passband during a first time period and configured to optically filter the images in the second set according to a second passband during a second time period.

19. The spectrometer of claim 9 wherein each detector element in the detector array is manufactured with a light detecting material having a first absorption length associated with the first spectral subset and a second absorption length associated with the second spectral subset, and wherein each detector element is configured to output first and second detector output signals associated with the first and second spectral subsets.

20. The spectrometer of claim 9 wherein the spatial filter comprises a coded aperture configured to spatially filter incident light according to a coded aperture function, and wherein the dispersion system is configured to two-dimensionally disperse images of the coded aperture in a wavelength dependent fashion onto the detector system.

21. The spectrometer of claim 20 wherein the processor is configured to process the detected images by applying an analysis function to one or more detector output signals corresponding to one or more detected images, wherein the analysis function complements the coded aperture function.

22. The spectrometer of claim 1 wherein at least two of the images in the first set at least partially overlap in the first direction.

23. The spectrometer of claim 1 wherein the second direction is perpendicular to the first direction.

24. A method of processing light comprising:

spatially filtering incident light radiated from a source with a spatial filter;

dispersing the filtered light to shift images of the spatial filter in a wavelength dependent fashion onto a detector system such that a first set of images corresponding to a first spectral subset of wavelengths are dispersed in a first direction, such that a second set of images corresponding to a second spectral subset of wavelengths are dispersed in the first direction, and such that at least one of the images in the first set at least partially overlap at least one of the images in the second set in a second direction different from the first direction; and

processing output signals corresponding to two or more detected images to distinguish signals associated with an image in the first set from signals associated with an overlapping image in the second set.

25. The method of claim 24 wherein dispersing the filtered light comprises dispersing the filtered light in two dimensions.

26. The method of claim 25 wherein dispersing the filtered light comprises dispersing the filtered light such that the first and second sets of images only partially overlap in the second direction.

27. The method of claim 25 wherein spatially filtering the incident light with a spatial filter comprises spatially filtering the incident light with a coded aperture defined by a coded aperture function.

28. The method of claim 27 wherein processing the output signals comprises applying an analysis function to the output signals, wherein the analysis function complements the coded aperture function.

29. The method of claim 27 wherein spatially filtering the incident light with a coded aperture comprises creating linearly independent spatial patterns in the incident light.

30. The method of claim 24 further comprising, prior to processing the output signals:

filtering the images of the first set according to a first passband corresponding to the first spectral subset; and

optically filtering the images of the second set according to a second passband corresponding to the second spectral subset.

31. The method of claim 30 wherein filtering the images in the first set comprises optically filtering the images in the first set using a first filter having the first passband, and wherein filtering the images in the second set comprises optically filtering the images in the second set using a second filter having the second passband.

32. The method of claim 31 wherein the detector system includes a two-dimensional detector array, wherein the first filter is integrated with each detector element in a first set of detector array elements, and wherein the second filter is integrated with each detector element in a second set of detector array elements.

33. The method of claim 30 wherein processing output signals comprises generating a first spectrum output based on detector output signals associated with the images filtered according to the first passband, and generating a second spectrum output based on detector output signals associated with the images filtered according to the second passband.

34. The method of claim 33 wherein processing the output signals further comprises generating a combined spectrum output based on the first and second spectrum outputs.

35. The method of claim 34 wherein the first and second passbands overlap, and wherein processing the output signals further comprises correcting for the overlap between the first and second passbands before generating the combined spectrum output.

36. The method of claim 33 wherein generating the first spectral output comprises:

generating a plurality of spectral estimates for each of two or more wavelengths in the first spectral subset;

averaging the plurality of first spectral estimates for each of the two or more wavelengths to generate wavelength-specific spectral estimates; and

generating the first spectral output based on the wavelength-specific spectral estimates.

37. The method of claim 30 wherein dispersing the filtered light comprises dispersing the filtered light such that images in the first set fully overlap the images in the second set.

38. The method of claim 30 wherein the filtering the images of the first set comprises filtering the images of the first set during a first time period according to the first passband, and wherein filtering the images of the second set comprises filtering the images of the second set during a second time period according to the second passband.

39. The method of claim 30 wherein each detector element in the detector system is manufactured with a light detecting material having a first absorption length associated with the first spectral subset and a second absorption length associated with the second spectral subset, and wherein filtering the first and second images comprises outputting first and second signals from each detector element associated with the first and second spectral subsets based on first and second absorption lengths associated with the detected light.

40. The method of claim 30 wherein spatially filtering the incident light with a spatial filter comprises spatially filtering the incident light with a coded aperture defined by a coded aperture function, and wherein dispersing the filtered light comprises dispersing images of the coded aperture in two dimensions in a wavelength dependent fashion.

41. The method of claim 24 wherein spatially filtering the incident light and dispersing the filtered light onto the detector system comprises spatially filtering the incident light with a static spatial filter and dispersing the filtered light with a static dispersion system onto a static detector system.

42. An optical spectrometer comprising:

a coded aperture configured to spatially filter incident light according to a coded aperture function;

a two-dimensional detector array;

a dispersion system disposed optically between the coded aperture and the detector array, said dispersion system configured to two-dimensionally shift images of the coded aperture in a wavelength dependent fashion onto the detector array;

wherein a first image of the coded aperture associated with a first wavelength overlaps a second image of the coded aperture associated with a second wavelength at the detector array; and

a processor configured to estimate at least one property of the incident light by applying an analysis function to one or more detector array output signals corresponding to one or more detected images, wherein the analysis function complements the coded aperture function.

43. The spectrometer of claim 42 wherein the first image vertically overlaps the second image.

44. The spectrometer of claim 42 wherein the first image vertically and horizontally overlaps the second image.

45. The spectrometer of claim 42 further comprising a third image of the coded aperture associated with a third wavelength, wherein the third wavelength is chromatically arranged between the first and second wavelengths, and wherein the third image does not overlap the first image at the detector array.

46. The spectrometer of claim 42 wherein the coded aperture is configured to create linearly independent spatial patterns in the incident light.

47. The spectrometer of claim 42 wherein the coded aperture function comprises a function defined by independent column codes.

48. The spectrometer of claim 42:

wherein the first image vertically and horizontally overlaps the second image; and

further comprising a third image of the coded aperture associated with a third wavelength, wherein the third wavelength is chromatically arranged between the first and second wavelengths, and wherein the third image does not overlap the first image at the detector array.

49. The spectrometer of claim 48 wherein the coded aperture is configured to create linearly independent spatial patterns in the incident light.

50. The spectrometer of claim 48 further comprising a fourth image of the coded aperture associated with a fourth wavelength, wherein the fourth wavelength is chromatically arranged after said third wavelength, and wherein the fourth image overlaps the third image at the detector array.

51. The spectrometer of claim 42 wherein said coded aperture comprises a static transmission mask.

52. A method of processing light comprising:

spatially filtering incident light radiated from a source with a coded aperture defined by a coded aperture function;

dispersing the filtered light in two dimensions to shift images of the coded aperture in a wavelength dependent fashion onto a two-dimensional detector array such that a first image of the coded aperture associated with a first wavelength overlaps a second image of the coded aperture associated with a second wavelength at the detector array; and

processing one or more output signals corresponding to one or more detected images to remove ambiguity between one or more overlapping images.

53. The method of claim 52 wherein processing the one or more output signals comprises applying an analysis function to one or more output signals corresponding to one or more detected images, wherein the analysis function complements the coded aperture function.

54. The method of claim 52 wherein the first image vertically overlaps the second image.

55. The method of claim 54 wherein the first image vertically and horizontally overlaps the second image.

56. The method of claim 52 wherein spatially filtering the incident light comprises creating linearly independent spatial patterns in the incident light.