Effect of birefringence on the modulation instabilities of a system of coherently coupled nonlinear Schroumldinger equations

A system of coherently coupled nonlinear Schroumldinger equations relevant to the polarization of light beams is considered. Modulation instability (MI) of plane waves is studied without approximations and two results were presented: (1) MI will be enhanced for a finite birefringence, thus extending earlier works that treated the low birefringence limit; (2) nonlinearity arising from phase coherence introduces unique regimes of cross-phase-modulation-induced MI.