The modulational instability of one-dimensional broad optical beams in biased two-photon centrosymmetric photorefractive crystals under steady-state conditions has been investigated.

Incoherently coupled dark-dark , bright-bright and bright-dark screening soliton pairs in centrosymmetric photorefractive crystals are possible due photorefractive effect.

Numerical simulations show that by this method chaotic synchronization can be achieved effectively no matter whether or not the coupling driving control of the injection lights is symmetrical.