Solitons in fiber amplifiers beyond the parabolic - gain and rate - equation approximations

We explore the existence of solitons in a nonlinear, dispersive, amplifying medium based on a model that makes neither the parabolic-gain approximation nor the rate-equation approximation. Without these approximations, the Maxwell-Bloch equations no longer reduce to a Ginzburg-Landau equation and do not appear to have analytic soliton solutions. We use numerical simulations to show that solitary waves can exist provided there is enough broadband loss such that the net gain is negative far away from the gain peak. In general, such solitons are chirped and the degree of chirp as well as the soliton width depend on the