Stabilization of a harmonic mode-locking by shifting the carrier frequency

Harmonically mode-locked soliton fiber lasers have been intensively investigated in recent years due to their wide range of applications. Drawback of these lasers is relatively large timing jitter which is significantly higher than the timing jitter in lasers operating at fundamental frequency. We report the stabilizing frequency shift effect in harmonic mode-locking ring soliton fiber laser that is studied theoretically and numerically. It is known that a harmonic mode-locking regime in a fiber laser occurs due to interpulse repulsion, which leads to a uniform distribution of pulses in the cavity. We demonstrate that the frequency shift contributes to an increase in the hardness of interpulse interactions and can led to stabilization of the periodic arrangement of pulses. The experiment carried out confirms the theoretical predictions and the results of numerical simulation.