| 摘要 |
A nonlinear optical receiver includes a source of coherent light of frequency omega for illuminating a spatial region. The portion of the source light which is reflected from objects within the spatial region constitutes a signal beam. A reference beam of coherent light of frequency omega is also provided. A photorefractive element receives the signal and reference beams and amplifies the signal beam by two-wave mixing. The receiver may include a first polarizer, having a first polarization direction, placed between a cubic photorefractive element and the signal and reference beams, and a second polarizer, having a second polarization direction perpendicular to the first polarization direction, placed so that the amplified signal beam must pass therethrough. A frequency shifting element, such as a Bragg cell modulator, is used to change the frequency of the reference beam. pa A first laser may provide both the source of coherent light and the reference beam of coherent light, or a first laser may provide the source of coherent light while a second laser provides the reference beam of coherent light. The photorefractive element may be a cubic photorefractive crystal or a nonlinear optic material. A two dimensional focal plane array may be added for detecting the amplified signal beam.
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