A Passively Mode-locked Tm-doped Fiber Laser Based on PbS Nanoparticles as Saturable Absorber

A passively mode-locked Tm-doped fiber laser was experimentally achieved by using PbS nanoparticles as a saturable absorber (SA), for the first time. The laser delivers stable conventional solitons with pulse duration of 1.24 ps at the repetition rate of 21.93 MHz. The centered wavelength and 3-dB bandwidth are 1957.37 nm and 3.43 nm, respectively. The high signal noise ratio of 61 dB indicates the good stability of the mode-locking. By further increasing pump power, the laser switches into stable second harmonic mode-locked regime. In this state, the average output power of 9.06 mW and repetition rate of 43.86 MHz are obtained. The results reveal that PbS is a type of promising SA for 2 μm ultra-short pulse generation.