Photorefractive square law converter

Details Photorefractive square law converter Photorefractive square law converter

1991-10-23

1993-03-02

Arnold, Bruce Y.

Optical: systems and elements

Holographic system or element

Having particular recording medium

359 1, 359 28, 359 30, 359244, 359290, 359292, 359322, G03H 102, G02F 100, G02B 2600

Patent

active

051914484

ABSTRACT:
A photorefractive device is provided for converting an image-bearing incoherent input beam to a high contrast coherent output beam the intensity of which varies as the square of the input intensity pattern. The device uses an incoherent image beam to write a holographic grating directly in a photorefractive medium. In one embodiment, a parallel, laterally displaced, telecentric system of lenses is used to split a quasi-monochromatic, incoherent image-bearing beam into two equal components. The two components are superimposed at the surface of the photorefractive medium to produce the hologram. In a second embodiment, the incoherent input beam is directed through a physically translating external grating to write the hologram in the photorefractive medium. The moving grating improves the diffraction efficiency of the hologram under the influence of an applied electric field and stabilizes the temporal response characteristics for signal processing. In both embodiments, the photorefractive medium is exposed to a coherent beam that picks up the image from the hologram and produces a coherent output beam having a high contrast replica of the input image.

REFERENCES:
patent: 4429954 (1984-02-01), Caulfield et al.
patent: 5062693 (1991-11-01), Beratan et al.

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