Tunable multi-pulse trains 1972 nm mode-locked fiber laser based on external mechanical modulation

Multi-pulse trains can be achieved by increasing the pump power from single-pulse mode-locking regime. Under high pump power, there is an inevitable risk of device damage, with SESAM devices being particularly susceptible. The external mechanical modulation method has been proposed to achieve multi-pulse trains. It has been demonstrated that six different multi-pulse mode-locking trains under the same pump power had been achieved by this method. The threshold generated by multi-pulses mode-locking trains was also decreased from 1.72 W to 1.47 W. External mechanical modulation acted as a handle to tune the nonlinear refractive index of a fiber. This adjustment directly changed the state of mode locking pulse. Therefore, this work provides a novel approach for tuning multi-pulse in 2 µm mode-locked fiber lasers.