Modulational instability of incoherently coupled beams in azobenzene-containing polymer with photoisomerization nonlinearity

The modulational instability of two incoherently coupled beams inazobenzene-containing polymer with photoisomerization nonlinearityis investigated analytically and numerically. Our results show thatas a precursor to spatial optical soliton formation, modulationalinstability can be adjusted and controlled by the wavelengthcombinations of the signal and background beams. We also discuss thedependences of strength of modulational instability on intensitiesof two signal beams and background beam. These findings make itpossible to predict the formation of incoherently coupled solitonpairs in azobenzene-containing polymer.