Modulation instability induced by cross-phase modulation in optical fibers

When two optical beams copropagate inside a single-mode fiber, the intensity-dependent refractive index couples the two beams through a nonlinear phenomenon known as cross-phase modulation (XPM). Such an XPM-induced interaction between the two waves can destabilize the steady state and lead to temporal modulations (self-pulsing) in the presence of group-velocity dispersion. This phenomenon is analogous to the modulation instability of a single beam occurring in the anomalous-dispersion regime of the fiber. The XPM-induced modulation instability can occur even in the normal-dispersion regime. The features of XPM-induced modulation instability are discussed in detail. This phenomenon may be useful for generating ultrashort pulses (<100 fs) in the visible region of the optical spectrum.