Structured coded aperture fiber bundles

• US 7,379,181 B2
• Filed: 06/02/2006
• Issued: 05/27/2008
• Est. Priority Date: 01/19/2006
• Status: Expired due to Fees

• Current Assignee: Optopo Inc.
• Original Assignee: Centice Corporation
• Inventors: Sullivan, Michael E., Brady, David J., Potuluri, Prasant
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US11/421,903
• Publication Number:
  US 20070165220A1
• Time in Patent Office: 725 Days
• Field of Search: 356/310, 356/326, 356/328, 356/330
• US Class Current: 356/326
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0216 using light concentrators or collectors or condensers
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/0221 the fibers defining an entry slit
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/2846 using modulation grid; Grid spectrometers
• CPC Class Codes: G02B 2207/129 Coded aperture imaging

Abstract

A spatial filter for an optical system, such as an optical spectrometer, collects and spatially filters light using a fiber bundle having a plurality of fibers disposed therein. At an input end of the fiber bundle, the fibers are typically packed tightly together to optimize the collection efficiency. At an output end, the fibers are spread out from the fiber bundle and arranged within a two-dimensional output area according to a two-dimensional pattern corresponding to a coded aperture function. As a result, the two-dimensional pattern of the output end spatially filters the light collected by the input end. Corresponding methods are also described.

Claims

1. A method of spatially filtering light radiating from a sample, the method comprising:

collecting light radiating from the sample with an input end of a fiber bundle comprising a plurality of optical fibers; and

spatially filtering the collected light by outputting the collected light from an output end of the fiber bundle, wherein the plurality of fibers at the output end are arranged according to a two-dimensional pattern corresponding to a pre-determined coded aperture function, wherein at least one column of the two-dimensional pattern includes at least two fibers from the ouput end of the fiber bundle, wherein at least one row of the two-dimensional pattern includes at least two fibers from the output end of the fiber bundle, and wherein each column of the two-dimensional pattern is orthogonal under an inner product transformation.

2. The method of claim 1 wherein the two-dimensional pattern corresponding to the pre-determined coded aperture function is distorted according to a distortion compensation function.

3. The method of claim 2 wherein the two-dimensional pattern comprises a grid pattern having a plurality of columns and rows, and wherein at least one of the columns and the rows are shaped according to the distortion compensation function.

4. The method of claim 1 further comprising varying a power level of light output by one or more of the plurality of fibers at the output end.

5. The method of claim 4 wherein varying the power level of light output by one or more of the plurality of fibers at the output end comprises attenuating the light output by one or more of the plurality of optical fibers at the output end of the fiber bundle using a second filter positioned proximate the output end of the fiber bundle.

6. The method of claim 1 wherein the input end of the fiber bundle comprises two or more separate subset input ends, each subset input end comprising two or more of the plurality of optical fibers, and wherein collecting light radiating from the sample comprises positioning different subset input ends of the fiber bundle proximate different areas of the sample to collect light radiating from different areas of the sample.

7. The method of claim 1 further comprising:

associating one or more illumination fibers with the fiber bundle;

coupling light from a light source into the one or more illumination fibers; and

illuminating the sample with incident light provided by the light source via the one or more illumination fibers.

8. The method of claim 1 wherein the coded-aperture function defines a plurality of transmissive areas and a plurality of non-transmissive areas, and wherein the two-dimensional pattern arranges the plurality of optical fibers at the output end such that the plurality of optical fibers correspond to the plurality of transmissive areas and such that areas between the plurality of optical fibers correspond to the plurality of non-transmissive areas.

9. The method of claim 1 wherein each of the plurality of fibers comprise a core surrounded by at least a portion of a cladding, and wherein the plurality of fibers at the input end are arranged such that first and second cores from adjacent first and second fibers are separated by a size of the corresponding claddings.

10. A method of manufacturing a spatial filter comprising:

positioning a plurality of optical fibers at a first end of a fiber bundle according to a two-dimensional pattern occupying a first area and corresponding to a pre-determined coded aperture function, wherein at least one column of the two-dimensional pattern includes at least two fibers from the output end of the fiber bundle, wherein at least one row of the two-dimensional pattern includes at least two fibers from the output end of the fiber bundle, and wherein each column of the two-dimensional pattern is orthogonal under an inner product transformation;

affixing the plurality of optical fibers in the two-dimensional pattern; and

packing a plurality of fibers at a second end of the fiber bundle, opposite the first end, into a second area smaller than the first area.

11. The method of claim 10 wherein the two-dimensional pattern comprises a grid pattern having a plurality of columns and rows.

12. The method of claim 11 wherein positioning the plurality of optical fibers comprises distorting at least one of the columns and rows of the grid pattern according to a pre-determined distortion compensation function prior to affixing the plurality of optical fibers in the two-dimensional pattern.

13. The method of claim 10 further comprising selecting each of the plurality of fibers in the fiber bundle from two or more different groups of fibers, wherein fibers in each of the different groups of fibers are designed to have different attenuations.

14. The method of claim 10 further comprising positioning a filter proximate the first end of the fiber bundle, wherein the filter attenuates light output by one or more of the plurality of optical fibers at the first end of the fiber bundle.

15. The method of claim 10 further comprising separating the second end of the fiber bundle into two or more subset ends, each subset end comprising two or more of the plurality of optical fibers.

16. The method of claim 10 further comprising associating one or more illumination fibers with the fiber bundle, said one or more illumination fibers configured to illuminate a sample by channeling illumination light provided by a light source to the sample.

17. The method of claim 10 wherein each of the plurality of fibers comprises a core surrounded by a cladding, and wherein packing the plurality of fibers at the second end of the fiber bundle comprises packing the plurality of fibers at the second end such that first and second cores from first and second adjacent fibers are separated by a thickness of the corresponding claddings.

18. The method of claim 17 further comprising removing at least a portion of the cladding from one or more of the plurality of fibers at the second end before packing the fibers into the second end.

19. The method of claim 10 wherein each of the plurality of fibers comprises a core surrounded by a cladding, the method further comprising removing at least a portion of the cladding from one or more of the plurality of fibers at the first end before positioning the plurality of fibers in the two-dimensional pattern.

20. The method of claim 10 wherein the first area is at least 1.3 times larger than the second area.

21. The method of claim 10 further comprising preparing an end surface of each of the plurality of fibers at the first and second ends for light propagation using at least one of a cleaving and a polishing technique.

22. An optical spatial filter comprising:

a fiber bundle comprising a plurality of optical fibers;

wherein said plurality of optical fibers are positioned at an output end of the fiber bundle according to a two-dimensional pattern occupying a first area and corresponding to a pre-determined coded aperture function;

wherein at least one column of the two-dimensional pattern includes at least two fibers from the output end of the fiber bundle;

wherein at least one row of the two-dimensional pattern includes at least two fibers from the output end of the fiber bundle;

wherein each column of the two-dimensional pattern is orthogonal under an inner product transformation; and

wherein said plurality of optical fibers at an input end of the fiber bundle, opposite said output end, are packed into a second area smaller than the first area.

23. The optical spatial filter of claim 22 wherein the two-dimensional pattern comprises a grid pattern having a plurality of columns and rows.

24. The optical spatial filter of claim 23 wherein the two-dimensional pattern corresponding to the pre-determined coded aperture function is distorted according to a distortion compensation function such that at least one of the columns and rows are distorted according to the distortion compensation function.

25. The optical spatial filter of claim 22 wherein the coded-aperture function defines a plurality of transmissive areas and a plurality of non-transmissive areas, and wherein the two-dimensional pattern arranges the plurality of optical fibers at the output end such that the plurality of optical fibers correspond to the plurality of transmissive areas and such that areas between the plurality of optical fibers correspond to the plurality of non-transmissive areas.

26. The optical spatial filter of claim 22 further comprising a second filter positioned proximate the output end of the fiber bundle, said second filter configured to attenuate light output by one or more of the plurality of optical fibers at the output end of the fiber bundle.

27. The optical spatial filter of claim 22 wherein the plurality of optical fibers are selected from two or more different groups of fibers, wherein fibers in each of the different groups are designed to have different attenuations.

28. The optical spatial filter of claim 22 wherein the input end comprises two or more separate subset input ends, each subset input end comprising two or more of the plurality of optical fibers.

29. The optical spatial filter of claim 22 further comprising one or more illumination fibers associated with the fiber bundle, said one or more illumination fibers configured to illuminate a sample by channeling illumination light provided by a light source to the sample.

30. The optical spatial filter of claim 22 wherein the first area is at least 1.3 times larger than the second area.

31. The optical spatial filter of claim 22 wherein each of the plurality of fibers comprise a core surrounded by at least a portion of a cladding, and wherein the plurality of fibers at the input end are arranged such that first and second cores from adjacent first and second fibers are separated by a thickness of the corresponding claddings.

32. The optical spatial filter of claim 22 wherein the plurality of optical fibers comprise a plurality of multi-mode fibers.

33. The optical spatial filter of claim 22 wherein the plurality of optical fibers comprise a plurality of single-mode fibers.

34. An optical spectrometer comprising:

a collection filter system configured to collect incident light radiating from a sample and spatially filter the collected light according to a pre-determined coded aperture function, the collection filter system comprising;

a fiber bundle comprising a plurality of optical fibers;

wherein said plurality of optical fibers are positioned at an output end of the fiber bundle according to a two-dimensional pattern occupying a first area and corresponding to the pre-determined coded aperture function; and

wherein said plurality of optical fibers at an input end of the fiber bundle, opposite said output end, are packed into a second area smaller than the first area;

a two-dimensional detector array; and

a dispersion system disposed between the collection filter system and the detector array, said dispersion system configured to shift images of the two-dimensional pattern in a wavelength dependent fashion onto the detector array.

35. The optical spectrometer of claim 34 wherein the two-dimensional pattern comprises a grid pattern having a plurality of columns and rows, and wherein the two-dimensional pattern corresponding to the pre-determined coded aperture function is distorted according to a distortion compensation function such that at least one of the columns and rows are distorted according to the distortion compensation function to compensate for distortion caused by optical characteristics of the optical spectrometer.

36. The optical spectrometer of claim 34 further comprising a filter positioned proximate the output end of the fiber bundle, said filter configured to attenuate light output by one or more of the plurality of optical fibers at the output end of the fiber bundle.

37. The optical spectrometer of claim 34 wherein the plurality of optical fibers are selected from two or more different groups of fibers, wherein fibers in each of the different groups are designed to have different attenuations.

38. The optical spectrometer of claim 34 further comprising:

a light source; and

one or more illumination fibers associated with the fiber bundle, said one or more illumination fibers coupled to the light source and configured to illuminate the sample with light provided by the light source.

39. The optical spectrometer of claim 34 wherein the first area is at least 1.3 times smaller than the second area.

40. The optical spectrometer of claim 34 further comprising a second filter disposed proximate the output end of the fiber bundle, said second filter configured to further spatially filter light output by the output end.

41. A method of processing light comprising:

collecting light radiating from a sample with an input end of a fiber bundle comprising a plurality of optical fibers;

spatially filtering the collected light by outputting the collected light from an output end of the fiber bundle, wherein the plurality of fibers at the output end are arranged according to a two-dimensional pattern corresponding to a pre-determined coded aperture function;

dispersing the filtered light to shift images of the two-dimensional pattern in a wavelength dependent fashion onto a two-dimensional detector array; and

processing one or more output signals corresponding to one or more detected images to identify one or more spectral characteristics of the light.

42. The method of claim 41 wherein the two-dimensional pattern corresponding to the pre-determined coded aperture function is distorted according to a distortion compensation function based on a known system distortion such that at least one of a column and a row of the two-dimensional pattern is distorted based on the distortion compensation function to compensate for distortion present in the detected images.

43. The method of claim 41 further comprising varying a power level of light output from one or more of the plurality of optical fibers at the output end.

44. The method of claim 43 wherein varying the power level of light output by one or more of the plurality of optical fibers comprises attenuating the light output by one or more of the plurality of optical fibers at the output end of the fiber bundle using a filter positioned proximate the output end of the fiber bundle.

45. The method of claim 41 wherein the input end of the fiber bundle comprises two or more subset input ends, each subset input end comprising two or more of the plurality of optical fibers.

46. The method of claim 41 further comprising:

associating one or more illumination fibers with the fiber bundle;

coupling light from a light source into the one or more illumination fibers; and

illuminating the sample with incident light provided by the light source via the one or more illumination fibers.

47. The method of claim 41 wherein each of the plurality of fibers comprise a core surrounded by at least a portion of a cladding, and wherein the plurality of fibers at the input end are arranged such that first and second cores from adjacent first and second fibers are separated by a thickness of the corresponding claddings.

48. The method of claim 41 further comprising filtering the spatially filtered light using a second filter disposed proximate the output end of the fiber bundle.