Graphene/WS₂ heterostructure saturable absorbers for ultrashort pulse generation in L-band passively mode-locked fiber lasers

Abstract

Graphene/WS₂ (G/WS₂) van der Waals (vdW) heterostructures are utilized as saturable absorbers (SAs) in compact mode-locked fiber lasers operating in the telecommunication L-band for the first time. The interlayer coupling is confirmed by Raman and photoluminescence spectra. In comparison with pure WS₂, the heterostructure exhibits excellent nonlinear optical properties in terms of larger modulation depth and lower saturation intensity due to the strong interlayer coupling. By incorporating the G/WS₂-based SA into an all-anomalous-dispersion fiber laser, stable conventional-soliton pulses with a pulse duration down to 660 fs can be realized at 1601.9 nm, manifesting better output performance compared to pure WS₂. In addition, through shifting the cavity dispersion to the net-normal dispersion, the G/WS₂ SA can also be applied for dissipative-soliton generation. Resultant output pulses feature the central wavelength of 1593.5 nm and the pulse duration of 55.6 ps. Our results indicate that the G/WS₂ vdW heterostructure is a promising candidate as SA for pulsed laser applications, which pave the way for the development of novel ultrafast photonic devices with desirable performance.