Modulational instability of incoherently coupled beams in biased photorefractive crystals

We study the one-dimensional modulational instability of incoherently coupled beams in biased photorefractive crystals under steady-state conditions. By globally treating the space-charge equation and only considering the local space-charge effect, i.e.; neglecting the higher-order terms in the space-charge equation, we obtain the global and local one-dimensional modulational instability growth rates of incoherently coupled beams in biased photorefractive crystals. Our results show that both the modulational instability growth rates can be adjusted and controlled by external bias field and the intensities of background beam and incoherently coupled signal beams.