Abstract

Optical instabilities can be classified as temporal or spatial depending on whether light is modulated temporally or spatially after its passage through the nonlinear medium. A temporal instability which has attracted considerable attention, known as the modulation instability, occurs through an interplay between self-phase modulation and anomalous dispersion. It manifests itself as the breakup of cw radiation into a train of ultrashort pulses. Its spatial analog corresponds to the development of a ring pattern on the transverse intensity profile of a cw beam in a self-focusing medium. The role played by anomalous dispersion in the case of temporal modulation instability is taken on by diffraction in the case of spatial instability. In this paper we study a spatio-temporal instability occurring when both diffraction and dispersion are present simultaneously. This instability is of fundamental importance as it shows how diffraction and dispersion act together to couple space and time. At the same time, it has the potential of practical applications since it can be used to convert a cw beam into a pulse train by spatially modulating the beam amplitude or phase.

© 1992 IQEC