Spatial shifts of the conjugate beam generated by a nondegenerate photorefractive phase-conjugate mirror.

We demonstrate that the phase conjugation of a beam during nondegenerate four-wave mixing is accompanied by a spatial shift relative to the degenerate conjugate-beam location. Experiments with a photorefractive phase-conjugate mirror reveal that the phase-conjugate beam shifts have a nonmonotonic dependence on the probe's detuning frequency and comprise both lateral displacements of up to 218 mum and angular tilts of up to 34 arc sec. An approximate theory based on spatial dispersion coefficients is in partial agreement with the experimental results.

Signal-to-noise ratio improvement by stochastic resonance in a unidirectional photorefractive ring resonator.

All-optical signal-to-noise ratio improvements by stochastic resonance have been obtained by use of the intensity bistability of a unidirectional photorefractive ring resonator. A signal-to-noise ratio gain of 10.5 dB has been obtained with a near-unity signal-to-noise ratio input signal at 6 mHz.

Image-contrast manipulation by the use of photorefractive ring multiresonators.

The nonlinear oscillations of photorefractive ring resonators that contain a microlens array are shown topermit controllable optical image-contrast compression and expansion.