Numerical analysis of the Raman spectrum evolution and soliton pulse generation in single-mode fibers

Numerical simulation is used to investigate the evolution of Raman spectra in the negative group-velocity dispersion regime of fibers for continuous-wave pump radiation. It is shown that the ratio of the pump power to the power of the fundamental soliton with a duration of approximately the inverse of the Raman gain linewidth is of great importance. Depending on its value, either cascade Raman scattering (with successive generation of the discrete Stokes components at relative frequency shifts of ~440 cm−1) or the generation of a Raman continuum is observed. In the time domain such a Raman continuum represents a random sequence of soliton-like pulses. The possibilities of the generation of a single solitonlike pulse from the Raman continuum are analyzed.