CoS nanosheets for generation of vector soliton and bound solitons in nonlinear optical fiber system

Transition metal chalcogenides (TMCs) with two-dimensional (2D) structures are of great interest for their extraordinary electrical, optical, magnetic, and mechanical properties. In this work, a novel cobalt sulfide (CoS) nanosheets (NSs) based saturable absorber (SA) with a modulation depth of 6.4 % is fabricated through liquid phase exfoliation (LPE) method, and successfully applied to a passive mode-locked erbium-doped fiber laser (PML-EDFL) for the first time as far as we know. By adjusting the pump power and optimizing the orientation of the intra-cavity polarization controller, a stable conventional solitons (CS) pulse with a duration of 905 fs and signal-to-noise ratio (SNR) of 58.5 dB at fundamental repetition frequency of 4.03 MHz, a pair of bound solitons with time interval of 4.9 ps between two 1.8 ps pulses are generated in proposed PML-EDFL. Meanwhile, the vector characteristics of generated soliton pulse are investigated, and polarization-locked vector solitons are observed. The results reveal that the CoS NSs have superior polarization insensitive nonlinear optical modulation properties and will find extensive application potential in the ultrafast photonics.