Self-injected spatial mode locking and coherent all-optical FM/AM switching based on modulational instability.

A geometric analysis of modulational instability reveals that spatiotemporally stable amplitude and frequency modulations may propagate in a nonlinear dispersive fiber, owing to self-injected locking of the temporal modes. We describe the close connection between the coherent nonlinear switching of an intense carrier by means of a weak modulating signal and similar instabilities in birefringent fibers and nonlinear directional couplers.