Modulation instabilities in asymmetric nonlinear fiber coupler

We have investigated the modulation instability (MI) in a nonlinear optical coupler using a generalized model describing the pulse propagation of two-core fiber. In particular, we discuss some influence of the MI of asymmetric nonlinear fiber coupler. The results show that input power and nonlinear coefficients of two cores influence the maximum value of the MI gain and MI bandwidth. When nonlinear coefficients of two cores are both negative, better modulation stability can be obtained than other situations. In particular, if the negative nonlinear coefficients are equal, the modulation instabilities will not appear.