Observation of Soliton Molecules in a Robust All PM Mode-Locked Fiber Laser With Nonreciprocal Phase Bias

We report the first experimental observation, to the best of our knowledge, of soliton molecules in a robust all polarization-maintaining (PM) mode-locked fiber laser with a nonreciprocal phase bias that results in a low self-starting threshold and stable mode locking. Through elaborately tuning the waveplate in the cavity, calibrating the laser pulse from conventional soliton to soliton molecules is implemented, and versatile soliton molecules including harmonic soliton pairs, tightly or loosely bound soliton quartets, multipulse bound solitons are achieved and manipulated at different pump powers. Theoretical investigations are established to elucidate the soliton molecules spectral characteristics with various phase differences and time separations in the cavity that elicit good concurrence with achieved experimental results. The achieved results both rich the nonlinear dynamics in fiber lasers and pave the potential applications for this excellent architecture fiber laser.