Modulation instability in the decreasing dispersion fibers with quintic nonlinearity

In case of co-existence of cubic and quintic nonlinearity,the condition and power gain spectra of modulation instability induced by the cross-phase modulation for two optical waves in loss,single-mode optical fibers are studied.In the normal dispersion region of the decreasing dispersion fibers,the effects of the quintic nonlinear coefficients,the dispersion longitudinal varying parameters,and the size relation of the two perturbation frequencies on the power gain spectra of modulation instability are analyzed in detail.The results indicate that,in case of quintic nonlinearity,the longitudinal decreasing of dispersion is still benefit to broaden the gain spectra of modulation instability.The positive quintic nonlinearity will make the width and the peak value of the gain spectra larger,and make the position of peak value be far away from the frequency of the main wave,while the negative quintic nonlinearity will do the opposite.If the size relation of the two perturbation frequencies is different,the dispersion longitudinal varying parameters will influence the position and value of the spectrum peak in different ways,and the quintic nonlinearity will intensify or suppress the modulation instability to different degrees.