Theory of soliton pulse forming in an actively modelocked fiber laser

Generation of subpicosecond solitons in active modelocked fiber lasers is investigated, both analytically and numerically. The laser model takes into account the pulse dispersive spreading, self-phase modulation, finite amplification bandwidth, pump depletion and Raman self-frequency shift. Our analytical theory, which is based on the inverse scattering method perturbation approach, allows us to calculate the steady-state parameters of the soliton pulse. The analytic predictions are confirmed by numerical simulation. It is shown that the minimal pulse duration may be achieved provided that the Raman self-frequency shift is suppressed by the phase modulator