Preparation of a 2D WS₂/MoS₂heterostructure via S-vacancy doping and its application in ultrafast laser modulation

Saturable absorbers (SAs) are core components in fiber lasers. In recent years, transition metal dichalcogenides have been widely used as SAs in fiber lasers due to their excellent saturable absorption performance. Here, two-dimensional (2D) WS₂/MoS₂heterojunctions with S vacancy defects are fabricated by regulating S vacancies. Based on this, a novel WS₂/MoS₂-based SA is prepared. Experimental results show that SAs achieve stable mode-locking phenomena in erbium-doped fiber lasers (EDFLs) and ytterbium-doped fiber lasers (YDFLs). In EDFLs, the WS₂/MoS₂-based SA (5 : 4) generates 682 fs pulses. In YDFLs, the WS₂/MoS₂-based SA (1 : 1) produces 748 fs pulses. Additionally, the WS₂/MoS₂-based SA (5 : 3) generates dual-wavelength pulses in the 1 µm and 1.5 µm bands in fiber lasers. Meanwhile, based on first-principles calculations, the dielectric constants of the WS₂/MoS₂heterojunction with S vacancies are calculated, achieving a clever combination of microscopic atomic structure and macroscopic optical properties. The presence of vacancy defects and heterostructures optimizes the optical modulation performance of the WS₂/MoS₂-based SA. This study not only provides a universal method for preparing WS₂/MoS₂-based SA but also theoretically explains the optimization of optical modulation by the vacancy defects and heterostructures, providing a reference in the development of two-dimensional SAs.