NbS2-nanosheet-based saturable absorber for 1.5 m and 2 m ultrafast fiber lasers

Niobium disulfide is a kind of transition metal dichalcogenides which has the advantages of large modulation depth, short excited carrier recovery time and high carrier mobility, theoretically being very suitable for the applications in ultrafast photonics. Up to now, there are few reports on the application of NbS2 in ultrafast optical devices, especially in the devices with long working wavelength, such as 2 & mu;m. In this work, few-layer NbS2 nanosheets were prepared by liquid exfoliation method and the NbS2-SA was prepared by covering the nano-sheets on tapered fiber. The device NbS2-SA exhibits good nonlinear saturable absorption property with a modulation depth of 10.2 % at 1550 nm. Based on the NbS2-SA, both 1.5 & mu;m and 2 & mu;m ultrafast fiber lasers are realized. The 1.5 & mu;m mode-locked fiber laser has a pulse width of 753 fs and the 2 & mu;m mode-locked fiber laser has an estimated pulse width of 5.77 ps and a maximum output power of 5.56 mW. All the results prove that NbS2 is an excellent broadband saturable absorption material.