Femtosecond Passively Er-Doped Mode-Locked Fiber Laser With WS2 Solution Saturable Absorber

This study presents the femtosecond fundamental and harmonic mode-locked Er-doped fiber laser with WS2 solution saturable absorber (SSA). The SA is fabricated based on a D-shaped fiber (DF) embedded in WS2 nanosheets solution. Such WS2 solution has virtues of good antioxidant capacity, excellent scattering resistance, high heat dissipation, and high damage threshold. This kind of SA shows a modulation depth of 11%, a saturable intensity I-sat of 5 MW/cm(2), and nonsaturable loss of 18%. By employing DF-WS2 SSA, a stable mode-locked fiber laser is achieved with repetition rate of 10.2 MHz and pulse duration of 660 fs. At the pump power of 350 mW, 460.7-MHz repetition rate harmonic mode-locking (HML) operation is also obtained, which corresponds to 45th harmonics of the fundamental cavity repetition rate. The pulse duration is 710 fs and signal-to-noise ratio is 66 dB, showing the excellent performance in HML fiber laser with SA. The results indicate that DF-WS2 solution can work as a potential SA for ultrafast nonlinear optics.