Self-starting passively mode-locked Yb-doped fiber lasers based on graded-index multimode fiber and fiber loop mirrors

We experimentally demonstrate self-starting stable noise-like pulse generation in Yb-doped passively mode-locked fiber lasers based on graded-index multimode fiber and fiber loop mirrors. The nonlinear loop mirror is employed in the ring-cavity to achieve self-starting mode-locking, the output pulses have a central wavelength of 1062.55 nm, a bandwidth of 6.8 nm, a fundamental repetition rate of 6.899 MHz, while the optical spectrum curves are basically the same under different pump powers. In order to obtain higher repetition-frequency pulses, the nonlinear amplifying loop mirror is implemented to realize self-starting noise-like pulses operation, while the pulses have a central wavelength of 1065.65 nm, a bandwidth of 4.9 nm, and a fundamental repetition rate of 16.5 MHz. We systematically are investigating the pump threshold power, optical spectrum, repetition frequency, pedestal pulse duration, peak width, and average output power.