Stable operating region in a harmonically actively mode-locked fiber laser

We theoretically study the recovery of a harmonically actively mode-locked soliton fiber laser from pulse dropout. In such lasers, a large number of pulses propagate simultaneously in the cavity. In order to obtain stable operation, pulses that are dropped due to changes in environmental conditions should recover, while other pulses that propagate in the cavity should remain stable. Soliton perturbation theory is used to find stability conditions for the noise in a time slot where a steady state pulse exists and in a time slot where a pulse is dropped. In the stable operating region of the laser, noise is stable in the presence of a pulse while noise becomes unstable in time slots where a pulse is dropped. Such a stability condition ensures that the laser can recover from accidental pulse dropout. A good agreement between the results of a reduced model and the results of a comprehensive numerical simulation was obtained. The results of this paper may enable to improve the stability of actively mode-locked fiber lasers.