Passively Q-Switched and Mode-Locked Fiber Laser Based on an ReS2 Saturable Absorber

Transition metal dichalcogenides, a family of two-dimensional material with unusual electronic, optical, mechanical, and electrochemical properties, have received much research attention in recent years. Here we demonstrate that, another type of few-layer transition metal dichalcogenides, rhenium disulfide (ReS₂) nanosheets display saturable absorption property at 1.55 μm. By incorporating the ReS₂ nanosheets with the polyvinyl alcohol (PVA), a film-type ReS₂-PVA saturable absorber is fabricated to realize Q-switching and mode locking of erbium-doped fiber lasers. The repetition rate of the Q-switched laser pulses varies from 12.6 to 19 KHz while the duration changes from 23 to 5.496 μs by tuning the pump from 45 to 120 mW. By optimizing the polarization state, the mode-locked operation is also obtained, emitting a train of pulses centered at 1558.6 nm with the duration of 1.6 ps and the fundamental repetition rate of 5.48 MHz. It is demonstrated that ReS₂ nanosheets have the similar saturable absorption property as that of MoS₂ and WS₂, and may find potential applications in pulsed laser, optical modulators, and sensors.