Control modulation instability in photorefractive crystals by the intensity ratio of background to signal fields.

By experimental measurements and theoretical analyses, we demonstrate the control of modulation instability in photorefractive crystals though the intensity ratio of coherent background to signal fields. Appearance, suppression, and disappearance of modulated stripes are observed in a series of spontaneous optical pattern formations, as the intensity of input coherent beam increases. Theoretical curves based on the band transport model give good agreement to experimental data, both for different bias voltages and different intensity ratios.