Modulation instability induced by cross-phase modulation.

Modulation instability that leads to break-up of intense cw radiation into a train of ultrashort pulses during its propagation in optical fibers occurs only in the presence of anomalous group-velocity dispersion. It is shown that a new kind of modulation instability can occur even in the normal-dispersion regime when two copropagating optical fields interact with each other through cross-phase modulation initiated by the nonlinearity. The quantitative aspects of this cross-phase- modulation-induced modulation instability are discussed and illustrated using a realistic experimental example.