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.