Noise-like square pulses in a linear-cavity NPR mode-locked Yb-doped fiber laser

• Noise-like square pulses are first generated in a linear-cavity fiber laser. • A fiber-pigtailed PBS is used as a NPR mode-locking element. • The compact linear-cavity configuration leads to low mode-locking threshold. We have first experimentally demonstrated the generation of noise-like square pulses (NLSPs) in a linear-cavity mode-locked Yb-doped fiber laser. The mode-locking mechanism is based on nonlinear polarization rotation (NPR) in our simple and compact linear-cavity configuration, in which a fiber-pigtailed polarization beam splitter (PBS) is used as a mode-locking element. The pulse duration of square pulses can be tuned from 2.92 ns to 12.06 ns with the amplitude remaining constant, and the maximum output average power is 75.4 mW with the slope efficiency of 23.69%, under our pump-power condition.