Abstract
We show by experimental measurements and theoretical analyses that there exists a pattern transition from optical modulation instability to transverse instability in nonlinear media. With the conditions of different input intensities and bias voltages, an input coherent beam propagating in the photorefractive crystals is observed to break up into stripe-filaments at a first threshold voltage. By modeling the periodic strip-filamens as cnoidal waves, we demonstrate that a second threshold voltage for forming dot-filaments comes from the transverse instability, resulting a good agreement with the experimental data. © 2009 Optical Society of America.