Incorporating MoS2 saturable absorption with nonlinear polarization rotation for stabilized mode-locking fibre lasers

Abstract

Stabilized hybrid mode-locking of erbium-doped fiber laser (EDFL) by incorporating strong MoS2 saturable absorber and weak nonlinear polarization rotation (NPR) is demonstrated. At threshold condition, the MoS2 starts the mode-locking of EDFL to provide a 680 fs wide pulsewidth with a time-bandwidth product of 0.407. With only the unintentionally weak NPR effect, the fluctuated EDFL pulsewidth ranged between 377 and 382 fs is observed with a tolerant half-wave-plate orientation angle of θHWP =21°. Adding MoS2 enhances the self-amplitude modulation (SAM) and shortens a pulsewidth to 305–330 fs with an allowable θHWP increasing up to 76°, implying the enhanced stabilization of passively mode-locking in EDFL. Enduing the weak NPR with strong saturable absorption (SA) effect significantly makes up the maximal SAM coefficient from 4.02 × 10−4 to 1 × 10−3, whereas the self-phase modulation (SPM) coefficient remains unaltered as that without adding the MoS2. The MoS2 saturable absorber additively offsets SAM beyond its threshold to enlarge the polarization tolerance without altering the SPM. Adjusting the polarization controller with unintentional polarization dependence affects the NPR induced polarization dependent loss so as to strengthen the SAM for mandatory mode-locking optimization of EDFL.