Resonantly induced mitigation of supermode noise in a harmonically mode-locked fiber laser: revealing the underlying mechanisms

We have performed experimental and numerical studies enabling clear insight into the physical mechanisms underlying the super-mode noise mitigation in harmonically mode-locked (HML) fiber lasers using the resonant continuous wave (CW) injection. New experiments have refined the requirements to the positions inside the laser spectrum assigned to the injected CW component, a Kelly sideband, and the transparency peaks of the birefringent fiber filter. In particular, we have proved experimentally that the noise mitigation effect is dominating with the CW injected to the long-wavelength side of laser spectrum. Injection to the opposite side destroys the HML operation regime. Our numerical simulations confirm these specific features. To get the result, we have simulated phase-locking between the CW and a single soliton. Then, the developed model has been applied to the laser cavity operating multiple pulses in the presence of the gain depletion and recovery mechanism responsible for harmonic pulse arrangement. We clearly demonstrate how the CW injection accelerates or slows down the HML process enabling the generation of additional inter-pulse forces.