Intermittent\n“Invisible” Soliton Pulsations\nInduced by the Temporal-Gain Dynamics in Passively Mode-Locked Fiber\nLasers

Gain, as one of the critical parameters in passively\nmode-locked\nfiber lasers (PMLFLs), fluctuates periodically in the time domain,\nincluding the fast depletion and slow recovery processes. Unfortunately,\nsince there are few soliton dynamics phenomena that can properly reflect\nits effect, time-varying gain is rarely considered a research topic\nin studying the nonlinear dynamics of fiber lasers. Here, based on\nthe transformation of soliton states, the effects of the temporal-gain\ndynamics (TGD) on soliton evolutions are theoretically speculated\nand experimentally demonstrated, and a novel nonlinear dynamics phenomenon\n- intermittent “invisible” pulsation (IIP) is reported.\nThe IIP is ultimately generated by the accumulation and consumption\nof gain residues. In addition to the fundamental frequency regime,\nthe generation of IIP is also observed in the harmonic mode-locking\nregime, and the evolution characteristics of each pulse train are\nvery similar to those in the fundamental frequency regime, demonstrating\nthe independence of the evolution of each pulse train during harmonic\nmode-locking IIP and verifying the universality of IIP. Apart from\nproviding new insights into the study of intermittent dynamics in\nultrafast lasers, this research will also provide new ideas for the\nstudy of TGD in ultrafast fiber lasers.