The dependence of mode-locking characteristics for 1.5  μ m laser on the composition ratio of WTe2/MoS2 SA

Heterojunctions take advantage of their tunable band structure, showing excellent optoelectronic properties and becoming a research hotspot in optoelectronic devices. In this work, saturable absorbers based on WTe2/MoS2 heterojunctions with three different ratios are successfully fabricated and characterized. The band structures and optical properties are calculated based on first principles. Three types of heterojunctions are employed for a stable mode-locking pulse in an Erbium-doped fiber laser. The heterojunction with a 5:5 ratio has a bandgap of 0.751 eV, which provides optimal bandgap matching with the photon energy at 1.5 μm. Experiments demonstrate that the 5:5 heterojunction exhibits the best performance, with a pulse width of 1.55 ps, a repetition rate of 3.324 MHz, a signal-to-noise ratio of 57.5 dB, and a modulation depth of 18.9%. These results demonstrate the great potential of tunable-ratio heterojunctions in optimizing the performance of fiber lasers.