Self-stabilization of dense soliton trains in a passively mode-locked ring laser

The generation of stable dense soliton trains in passively mode-locked ring fiber lasers was explored theoretically. We found equilibrium states of even and odd numbers of interacting solitons in a ring configuration by employing soliton perturbation theory. In a lossless ring, these equilibrium states were unstable due to the lack of a damping mechanism both for the oscillations in the solitons parameters as well as for modulation instability. In a passively mode-locked ring fiber laser, these dense soliton trains were self-stabilized to form ordered trains. The stabilization process was initiated by the local repulsive soliton-soliton interactions and preceeded by a global soliton phase locking stemming from multimode self-injection locking. We describe in detail the evolution from a disordered to ordered dense soliton train.