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A spectral imager includes an elongate light propagation medium that receives light at one end, has graded average spectral absorption properties in the elongate direction, and spectral detectors distributed in the elongate direction. The spectral absorption properties of the medium can be graded in

A spectral imager includes an elongate light propagation medium that receives light at one end, has graded average spectral absorption properties in the elongate direction, and spectral detectors distributed in the elongate direction. The spectral absorption properties of the medium can be graded in both elongate and transverse directions. Both linear and two-dimensional arrays can be formed, enabling simultaneous hyperspectral detection.

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We claim: 1. A spectral imager comprising: a first elongate light propagation medium arranged to receive light at one end, and structured to have a spectral absorption coefficient gradient in the elongate direction, detectors distributed along said medium in the elongate direction to detect light a

We claim: 1. A spectral imager comprising: a first elongate light propagation medium arranged to receive light at one end, and structured to have a spectral absorption coefficient gradient in the elongate direction, detectors distributed along said medium in the elongate direction to detect light absorbed by said medium, wherein the spectral absorption properties of said medium are graded in the elongate direction along a first surface of said medium, wherein the spectral absorption properties of said medium along said first surface are graded from lower to higher wavelengths in the direction of light propagation through said medium, wherein said medium includes a second surface opposite said first surface, and wherein the spectral absorption properties of said medium along said second surface are ungraded in the direction of light propagation through said medium. 2. The spectral imager of claim 1, wherein said first and second surfaces are angled to each other. 3. The spectral imager of claim 1, wherein said first and second surfaces are parallel to each other. 4. The spectral imager of claim 1, wherein the spectral absorption properties of said medium are substantially uniform in a direction transverse to said elongate direction. 5. The spectral imager of claim 1, wherein said first and second medium surfaces in the elongate direction that are angled to each other. 6. The spectral imager of claim 1, further comprising optical resonator cells distributed along said medium in the elongate direction and tuned to the spectral absorption properties of said medium at their respective locations. 7. The spectral imager of claim 6, said resonator comprising distributed Bragg reflectors along a first elongate surface of said medium. 8. The spectral imager of claim 1, further comprising a readout circuit connected to said detectors to sense the spectral characteristic of light propagating through said medium. 9. The spectral imager of claim 8, wherein said readout circuit includes circuitry to obtain a readout of a different functionality from less than all of said detectors. 10. The spectral imager of claim 8, wherein said readout circuit includes circuitry to monitor continuously each of said detectors, and to obtain a timed readout from less than all of said detectors at a desired time. 11. The spectral imager of claim 1, further comprising additional elongate light propagation media and respective detectors similar to said first medium and its detectors, all of said media collectively comprising a pixel array. 12. The spectral imager of claim 11, wherein said media are optically isolated from each other. 13. The spectral imager of claim 11, said pixel array comprising a linear array. 14. The spectral imager of claim 11, said pixel array comprising a two-dimensional array. 15. The spectral imager of claim 14, said two-dimensional array comprising a plurality of stacked linear arrays. 16. The spectral imager of claim 1, wherein said light propagation medium is substantially linear. 17. The spectral imager of claim 1, wherein said light propagation medium is curved. 18. The spectral imager of claim 1, further comprising an optical collector directing light to said one end of the medium. 19. The spectral imager of claim 18, wherein said light collector redirects light substantially transverse to said elongate medium to a path generally in the elongate direction of said medium. 20. The spectral imager of claim 19, wherein said light collector is substantially square or circular, and said light propagation medium is curved to fit within an area less than the area of said light collector. 21. The spectral imager of claim 1, wherein said medium's length is at least an order of magnitude greater than its thickness. 22. A spectral imager comprising: a first elongate light propagation medium arranged to receive light at one end, and structured to have a spectral absorption coefficient gradient in the elongate direction, detectors distributed along said medium in the elongate direction to detect light absorbed by said medium, wherein the spectral absorption properties of said medium are graded in the elongate direction along a first surface of said medium, wherein the spectral absorption properties of said medium along said first surface are graded from lower to higher wavelengths in the direction of light propagation through said medium, wherein said medium includes a second surface opposite said first surface, wherein the spectral absorption properties of said medium along said second surface are graded in the direction of light propagation through said medium, but at lesser absorption wavelengths than along said first surface at corresponding distances in the elongate direction. 23. The spectral imager of claim 22, wherein said first and second surfaces are parallel to each other. 24. The spectral imager of claim 22, wherein the spectral absorption properties of said medium are substantially uniform in a direction transverse to said elongate direction. 25. The spectral imager of claim 24, wherein said first and second medium surfaces in the elongate direction that are angled to each other. 26. The spectral imager of claim 22, further comprising optical resonator cells distributed along said medium in the elongate direction and tuned to the spectral absorption properties of said medium at their respective locations. 27. The spectral imager of claim 26, said resonator comprising distributed Bragg reflectors along a first elongate surface of said medium. 28. The spectral imager of claim 22, further comprising a readout circuit connected to said detectors to sense the spectral characteristic of light propagating through said medium. 29. The spectral imager of claim 28, wherein said readout circuit includes circuitry to obtain a readout of a different functionality from less than all of said detectors. 30. The spectral imager of claim 28, wherein said readout circuit includes circuitry to monitor continuously each of said detectors, and to obtain a timed readout from less than all of said detectors at a desired time. 31. The spectral imager of claim 22, further comprising additional elongate light propagation media and respective detectors similar to said first medium and its detectors, all of said media collectively comprising a pixel array. 32. The spectral imager of claim 31, wherein said media are optically isolated from each other. 33. The spectral imager of claim 31, said pixel array comprising a linear array. 34. The spectral imager of claim 31, said pixel array comprising a two-dimensional array. 35. The spectral imager of claim 34, said two-dimensional array comprising a plurality of stacked linear arrays. 36. The spectral imager of claim 22, wherein said light propagation medium is substantially linear. 37. The spectral imager of claim 22, wherein said light propagation medium is curved. 38. The spectral imager of claim 22, further comprising an optical collector directing light to said one end of the medium. 39. The spectral imager of claim 38, wherein said light collector redirects light substantially transverse to said elongate medium to a path generally in the elongate direction of said medium. 40. The spectral imager of claim 39, wherein said light collector is substantially square or circular, and said light propagation medium is curved to fit within an area less than the area of said light collector. 41. The spectral imager of claim 22, wherein said medium's length is at least an order of magnitude greater than its thickness. 42. A graded optical medium, comprising: an elongate optical medium having spectral absorption properties which are graded both in the elongate direction of said medium and in a direction transverse to said elongate direction, said medium having opposed elongate surfaces, wherein its spectral absorption properties are graded along both of said surfaces in the elongate direction, but the medium at one of said surfaces absorbs higher wavelength light than at the other surface at corresponding elongate distances along the medium. 43. The graded optical medium of claim 42, wherein said opposed surfaces are parallel. 44. The graded optical medium of claim 42, further comprising sets of distributed Bragg reflectors distributed in an elongate direction along a surface of the medium. 45. The graded optical medium of claim 42, wherein said medium's length is at least an order of magnitude greater than its thickness. 46. The graded optical medium of claim 42, further comprising sets of distributed Bragg reflectors distributed in an elongate direction along a surface of the medium. 47. The graded optical medium of claim 42, wherein said medium's length is at least an order of magnitude greater than its thickness. 48. A method of fabricating a spectral imager, comprising: growing an optical medium on a substrate with a graded spectral absorption in a direction transverse to the substrate, and an elongate dimension parallel to the substrate; establishing a spectral absorption gradient in said medium along its elongate direction; and removing said substrate from the said medium after varying the medium's thickness; wherein said spectral absorption gradient is established by varying the medium's thickness along its elongate direction; wherein the thickness of said medium is varied by forming a bevel in the medium opposite said substrate; and wherein said medium is graded away from said substrate to a higher absorption wavelength, and said bevel is formed so that the thickness of said medium transverse to the substrate increases in the direction of increasing average spectral absorption. 49. The method of claim 48, further comprising distributing optical detectors along said medium in its elongate direction. 50. The method of claim 49, further comprising connecting a readout circuit to said detectors. 51. A method of fabricating a spectral imager, comprising: growing an optical medium on a substrate with a graded spectral absorption in a direction transverse to the substrate, and an elongate dimension parallel to the substrate; establishing a spectral absorption gradient in said medium along its elongate direction; removing said substrate from the said medium after varying the medium's thickness; wherein said spectral absorption gradient is established by varying the medium's thickness along its elongate direction, and wherein the thickness of said medium is varied by forming a bevel in the medium opposite said substrate, and a parallel bevel is formed in the medium opposite the first bevel after the substrate has been removed. 52. The method of claim 51, further comprising distributing optical detectors along said medium in its elongate direction. 53. The method of claim 52, further comprising connecting a readout circuit to said detectors. 54. The method of claim 53, wherein said readout circuit is connected by flip-chip bonding. 55. The method of claim 51, wherein said optical medium is grown as a thin layer on said substrate, further comprising channeling said layer in its elongate direction with optically nonconductive spacings between channels to form a layer of parallel, optically isolated optical channels which establish a linear pixel array at one end. 56. The method of claim 55, further comprising forming additional similar layers of parallel, optically isolated optical channels which establish respective linear pixel arrays at one end, and stacking said layers to form a two-dimensional pixel array. 57. A graded optical medium, comprising: an elongate optical medium having spectral absorption properties which are graded both in the elongate direction of said medium and in a direction transverse to said elongate direction, said medium having opposed elongate surfaces, wherein the spectral absorption properties of said medium are graded along only one of said surfaces in the elongate direction; and sets of distributed Bragg reflectors distributed in an elongate direction along a surface of the medium. 58. A graded optical medium, comprising: an elongate optical medium having spectral absorption properties which are graded both in the elongate direction of said medium and in a direction transverse to said elongate direction, said medium having opposed elongate surfaces, wherein the spectral absorption properties of said medium are graded along only one of said surfaces in the elongate direction; wherein said medium's length is at least an order of magnitude greater than its thickness. 59. A method of fabricating a spectral imager, comprising: growing an optical medium on a substrate with a graded spectral absorption in a direction transverse to the substrate, and an elongate dimension parallel to the substrate; establishing a spectral absorption gradient in said medium along its elongate direction; distributing optical detectors along said medium in its elongate direction; and connecting a readout circuit to said detectors; wherein said spectral absorption gradient is established by varying the medium's thickness along its elongate direction; wherein the thickness of said medium is varied by forming a bevel in the medium opposite said substrate; wherein said medium is graded away from said substrate to a higher absorption wavelength, and said bevel is formed so that the thickness of said medium transverse to the substrate increases in the direction of increasing average spectral absorption; and wherein said readout circuit is connected by flip-chip bonding. 60. A method of fabricating a spectral imager, comprising: growing an optical medium on a substrate with a graded spectral absorption in a direction transverse to the substrate, and an elongate dimension parallel to the substrate; and establishing a spectral absorption gradient in said medium along its elongate direction; wherein said spectral absorption gradient is established by varying the medium's thickness along its elongate direction; wherein the thickness of said medium is varied by forming a bevel in the medium opposite said substrate; wherein said medium is graded away from said substrate to a higher absorption wavelength, and said bevel is formed so that the thickness of said medium transverse to the substrate increases in the direction of increasing average spectral absorption; and wherein said optical medium is grown as a thin layer on said substrate, further comprising channeling said layer in its elongate direction with optically nonconductive spacings between channels to form a layer of parallel, optically isolated optical channels which establish a linear pixel array at one end. 61. The method of claim 60, further comprising forming additional similar layers of parallel, optically isolated optical channels which establish respective linear pixel arrays at one end, and stacking said layers to form a two-dimensional pixel array.