Curious features of nonlinear pulse propagation in single-mode optical fibers

Abstract

Numerical simulations of the propagation of high-intensity pulses in single-mode optical fibers, and the subsequent compression of such pulses in a grating-pair compressor, have shown some curious features. For a wide range of parameters the pulses exhibit a phenomenon which we describe as optical wave breaking, in which the inner parts of a pulse overtake the pulse tails, resulting in a high-frequency modulation on the pulse, and the generation of new frequency components. Numerical simulations with sufficient resolution to model this effect predict some previously unexplained features in the spectrum of the pulses which have been used to achieve the highest compression yet reported.1 Simulations including the wave-breaking effect, and a linear fiber loss, quite accurately predict the results of those experiments, thus extending the range of validity of the nonlinear Schroedinger equation for describing nonlinear pulse propagation in single-mode fibers. Simulations including the effects of a finite response time for part of the nonlinear index of the fiber have demonstrated the existence of an instability, better known as stimulated Raman gain, which limits the usefulness of this technique for long input pulses.