Generation of a Train of Ultrashort Pulses from cw Light using Cross-phase Modulation and Raman Amplification in Optical Fibers

Abstract

A novel method that can lead to generation of a train of ultrashort optical pulses from cw light in the anomalous-dispersion regime of single-mode fibers is proposed. It consists of copropagating a CW signal with a train of intense pump pulses in an optical fiber whose minimum-dispersion wavelength is chosen such that it falls between the pump and the signal wavelength. The pump pulses impose nearly linear frequency chirps on the signal through cross-phase modulation and at the same time amplify the signal through stimulated Raman scattering, which induce the cw signal to evolve into a train of ultrashort pulses. Numerical simulations show that the generated signal pulses are nearly chirp free and pedestal free and are much shorter than the pump pulses. The higher the pump power is, the narrower and more intense the generated signal pulse is, and a shorter fiber is used. Finally, it is shown that the method remains applicable even for a small walk-off between the pump and the signal pulses.