Simple computational model of image correlation by four-wave mixing in photorefractive media

Abstract

A simple systems-oriented model of image correlation by nondegenerate four-wave mixing in photorefractive media is discussed, and its computational implementation is described. The model is based on a linear-incomplex modulation index formulation and is capable of describing the correlation product in a wide range of experimental conditions. Bragg matching effects on the test and reference images are explicitly included. The comparison of calculated results with experimental results is excellent, and a discussion of higher-order theories of the photorefractive effect is given. The model is currently being used to optimize the performance of experimental correlators.

Bandwidth study of volume holography in photorefractive InP:Fe for femtosecond pulse readout at 15 μm

“…Because of the strong spatial Bragg selectivity of volume holograms, photorefractive crystals are excellent for high-capacity holographic data storage 6 by use of angular multiplexing and for narrow-band interference filtering, 7 but they are considered as not well suited for implementing Fourier-plane filtering operations in space-domain image processing 8 because the Bragg selectivity performs the function of a spatial filter and limits the field of view. 9,10 Special designs, such as the Galilean telescopic beam compression technique in a jointtransform correlator, 11 had to be used to solve the problem. Even holographic memories experience limitations in storage density owing to the Bragg selectivity when volume holograms are written and read out by lasers with greatly different wavelengths, although this is not a problem for identical write and readout wavelengths.…”

Shift-invariant photorefractive joint-transform correlator using Fe:LiNbO_3 crystal plates

“…Assuming the reference beam and the readout beam are nearly counterpropagating, as the object image is spatially shifted inside the object plane, the new gratings written by the object and the reference waves are always nearly satisfying the Bragg conditions for the fixed readout beam. Rela tively large shift invariance is expected in the object plane, which has been experimentally demonstrated by Nicholson et al 7 For the reference plane, how ever, the shift invariance becomes much more strin gent. This is because, when the reference image is shifted horizontally inside the reference plane, the newly formed gratings tilt away from the fixed read out beam, introducing a phase mismatch in the diffraction process.…”

“…Over the past few years, a variety of real-time optical image correlators have been demonstrated by using either a spatial light modulator or a photorefractive crystal in the Fourier domain. [3][4][5][6][7][8][9] Although the technology of spatial light modulators has advanced rapidly, the devices still have poor resolutions compared with photorefractive crystals. Photorefractive crystals have the capability of real-time operation and an extremely high sensitivity for certain materials such as sillenites and compound semiconductors.…”

<title>Holography in biosciences</title>

“…Applications on holographic matched filtering [31][32][33], holographic interferometry [34] and moire holography [15] have been described in the literature.…”