Transition metal dichalcogenide (WS₂ and MoS₂) saturable absorbers for Q-switched Er-doped fiber lasers

This report demonstrates a stable Q-switched Er-doped fiber laser with MoS₂ (WS₂)-based saturable absorber (SA) in the net normal dispersion regime. The SA is obtained by mixing MoS₂ (WS₂) nanosheets with polyvinyl alcohol (PVA) into polystyrene cells, and then evaporating them to form MoS₂ (WS₂)/PVA film. The modulation depth values for MoS₂/PVA and WS₂/PVA are measured to be 2.7% and 2.1% respectively. Employing the MoS₂ (WS₂)/PVA film in the Er-doped fiber laser cavity, stable Q-switching operation is achieved with central wavelength of 1560 nm. The shortest pulse durations of the two Q-switched fiber lasers are, respectively, 3.97 and 3.71 µs, and their maximum single pulse energies are measured to be 131.52 and 126.96 nJ. The experimental results clearly show that MoS₂ (WS₂) is a promising nonlinear material, and that improvements in Q-switching performance due to two SAs in the net normal dispersion regime might be helpful in the design of fiber lasers. (paper)