Dynamics of ultrashort-pulse generation by Raman fiber lasers: cascade self-mode locking, optical pulsons, and solitons

The dynamics of ultrashort-pulse generation in Raman fiber lasers is numerically investigated. The regime of cascade self-mode locking in the process of generation of higher-order Stokes components as well as formation of ultrashort solitary pulses with a high contrast of radiation are described. The generation of optical solitons at the Stokes frequency is shown to be the result of a cooperative effect of self-phase modulation, negative group-velocity dispersion, and distributed stimulated Raman scattering. In the same way we explain the formation of pulses with regularly pulsating amplitude and frequency modulation; we call these optical pulsons.