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A wavelength conversion device includes a photodetector for generating a photocurrent in response to the detection of radiation at a first wavelength. An avalanche multiplier amplifies the signal photocurrent and feeds this to a light emitting element that produces radiation at a second wavelength s

A wavelength conversion device includes a photodetector for generating a photocurrent in response to the detection of radiation at a first wavelength. An avalanche multiplier amplifies the signal photocurrent and feeds this to a light emitting element that produces radiation at a second wavelength shorter than the first wavelength and corresponding to the detected radiation at the first wavelength. The components are assembled together in an integrated stacked arrangement either by epitaxial growth or wafer fusion of the individual components. The device is useful as an image intensifier or thermal imaging device.

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We claim: 1. A wavelength conversion device comprising: a photodetector for generating a photocurrent in response to the detection of radiation at a first wavelength; an avalanche multiplier for amplifying said photo current; and a light emitting element driven by said amplified photocurrent to pro

We claim: 1. A wavelength conversion device comprising: a photodetector for generating a photocurrent in response to the detection of radiation at a first wavelength; an avalanche multiplier for amplifying said photo current; and a light emitting element driven by said amplified photocurrent to produce radiation at a second wavelength different from said first wavelength and corresponding to detected radiation at said first wavelength; wherein said photodetector, said avalanche multiplier, said light emitting element are arranged in a stacked innervated structure selected from the group consisting of: a structure wherein said photodetector, said avalanche multiplier, and said light emitting element are located on different wafers which are fusion bonded together, and a structure wherein functional layers of said photodetector, said avalanche multiplier, and said light emitting element are epitaxial layers grown on a common substrate. 2. A wavelength conversion device as claimed in claim 1, wherein said second wavelength is shorter than said first wavelength. 3. A wavelength conversion device as claimed in claim 2, wherein said photodetector is integrated onto a transparent substrate through which said radiation at a first wavelength passes to impinge on said photodetector. 4. A wavelength conversion device as claimed in claim 3, wherein said integrated stacked arrangement comprises III-V semiconductors. 5. A wavelength conversion device as claimed in claim 4, wherein said light emitting element is a light emitting diode. 6. A wavelength conversion device as claimed in claim 5, wherein said photodetector comprises InxGa1-xAs/InP layers. 7. A wavelength conversion device as claimed in claim 6, wherein said avalanche multiplier and said LED comprise InP and InPAs layers, respectively. 8. A wavelength conversion device as claimed in claim 7, wherein said layers are epitaxial layers. 9. A wavelength conversion device as claimed in claim 6, wherein said avalanche multiplier and said light emitting diode comprise GaAs and GaAs/AlGaAs layers respectively. 10. A wavelength conversion device as claimed in claim 3, wherein said first wavelength lies in the infrared range and said second wavelength lies in the near infrared or visible range. 11. A wavelength conversion device as claimed in claim 10, wherein said first wavelength lies in the range of 1.1 to 1.65 microns. 12. A wavelength conversion device as claimed in claim 1 wherein said photodetector and light emitting element are provided with optical windows to permit pixelless up conversion of an image. 13. A wavelength conversion device as claimed in claim 1, comprising an array of said stacked arrangements arranged in parallel to permit pixellized up conversion of an image. 14. A wavelength conversion device as claimed in claim 13, wherein said stacked arrangements are located on a common transparent substrate. 15. A thermal imaging device comprising: a) at least one integrated stack including: (i) a photodetector for generating a photocurrent in response to the detection of far infrared radiation; (ii) an avalanche multiplier for amplifying said photocurrent; and (iii) a light emitting diode driven by said amplified photocurrent to produce near infrared or visible radiation corresponding to said detected far infrared; and (iv) wherein said photodetector, said avalanche multiplier, and said light emitting element are arranged in a stacked integrated structure selected from the group consisting of: a structure wherein photodetector, said avalanche multiplier, and said light emitting diode are gown on different wafers which are fusion bonded together, and a structure wherein said functional layers of said photodetector, said avalanche multiplier, and said light emitting diode are epitaxial layers grown an a common substrate; and b) a camera for generating an image from said near infrared or visible radiation. 16. A thermal imaging device as claimed in claim 15, comprising an array of said integrated stacks on a common transparent substrate to provide a pixellated output. 17. A thermal imaging device as claimed in claim 16, wherein said camera is a charge coupled device having individual elements opposing said respective integrated stacks. 18. A thermal imaging device as claimed in claim 16, further comprising a micro-lens fabricated on the surface of said light emitting element. 19. A thermal imaging device as claimed in claim 15, comprising window openings to permit the formation of a pixelless image, and said camera is a charge-coupled device. 20. A thermal imaging device as claimed in claim 15, wherein said integrated stack comprises a III-V material system.