Abstract

Modulation instability refers to a process in which weak perturbations from the steady state grow exponentially as a result of an interplay between the nonlinearity and the group-velocity dispersion. In the context of optical fibers modulation instability requires anomalous dispersion and manifests as breakup of the cw or quasi-cw radiation into a train of ultrashort pulses.¹ This paper shows that a new kind of modulation instability can occur even in the normal dispersion regime when more than one optical field copropagates inside the fiber. The physical mechanism behind this novel phenomenon is cross-phase modulation that invariably accompanies the nonlinearity-induced self-phase modulation. The modulation-instability-induced gain and the frequency range over which the gain occurs are studied by including the effect of group-velocity mismatch. Numerical results are presented for the realistic case of propagation around 0.53 μm.

© 1987 Optical Society of America