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We show that a soliton of the nonlinear Schrödinger equation perturbed by filter losses and/or the finite gain bandwidth of amplifiers can be kept stable by saturable absorbers with a relaxation time much longer than the width of the soliton. This provides for ultrashort pulse generation with a slow saturable absorber only and may have possible applications in the stabilization of soliton storage rings.
Kärtner et al. (Sun,) studied this question.