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

Graphene/WS (G/WS) 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 WS, 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/WS-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 WS. In addition, through shifting the cavity dispersion to the net-normal dispersion, the G/WS 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/WS 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.