Cross-phase modulation induced modulation instability in single-mode optical fibers with saturable nonlinearity

Taking into account the saturable nonlinearity of the single-mode optical fibers, condition and gain spectra of scalar modulation instability induced by cross-phase modulation of two optical waves of different frequencies with the same polarizations are investigated. In both of the normal and anomalous dispersion regions, the contour plots of gain spectra of modulation instability with gray levels, the critical perturbation frequency (or instability domain), and the peak perturbation gain versus the input powers of the two waves are analyzed and discussed. The results show that, the critical perturbation frequency (or instability domain) and the peak perturbation gain increase with the input power, reaching a maximum value, and then decrease. This leads to a unique value of peak perturbation gain and critical perturbation frequency for two different input powers.