WS₂ saturable absorber for dissipative soliton mode locking at 1.06 and 1.55 μm

Transition-metal dichalcogenides, such as tungsten disulfide (WS₂) and molybdenium disulfide (MoS₂), are highly anisotropic layered materials and have attracted growing interest from basic research to practical applications due to their exotic physical property that may complement graphene and other semiconductor materials. WS₂ nanosheets are found to exhibit broadband nonlinear saturable absorption property, and saturable absorbers (SAs) are fabricated by depositing WS₂ nanosheets on side-polished fibers. Attributing to the weak evanescent field and long interaction length, the WS₂ nanosheets are not exposed to large optical intensity, which allows the SA to work at the high-power regime. The SAs are used to mode lock erbium- and ytterbium-doped fiber lasers with normal dispersion, producing trains of dissipative soliton at 1.55 and 1.06 μm respectively. Simulations show that the bandgap of WS₂ nanosheets decreases from 1.18 to 0.02 and 0.65 eV by introducing W and S defects respectively, which may contribute to the broadband saturable absorption property of the WS₂.