Lead Sulfide Saturable Absorber Based Passively Mode-locked Tm-doped Fiber Laser

In this paper, a passively mode-locked Tm-doped fiber laser by employing lead sulfide (PbS) nanoparticles as the saturable absorber (SA) is successfully demonstrated in the 2 μm region for the first time, to the best of our knowledge. Measured by a home-made balanced twin-detector setup at 2 μm, the PbS SA was characterized by the modulation depth of 10.69%, the non-saturable loss of 74.27%, and the saturable peak intensity of 8.62 MW/cm2, respectively. The laser delivered stable conventional soliton with a pulse duration of 1.24 ps and a repetition rate of 21.93 MHz. The center wavelength and 3 dB bandwidth are 1957.37 nm and 3.43 nm, respectively. Additionally, the second-order harmonic soliton pulses with a repetition rate of 43.86 MHz were also observed by further increasing the pump power. Our work reveals that PbS material is a reliable SA applied for pulse generation in the 2 μm spectral region.