Low repetition rate microsecond square pulse generation in a passively mode-locked Yb-doped fiber laser

We demonstrate that a low repetition rate, all-fiber passively mode-locked Yb-doped fiber laser through nonlinear polarization rotation (NPR). A 1000 m long single-mode fiber (SMF) is inserted into the cavity to lower the repetition rate. The laser operates in dissipative soliton resonance (DSR) region and generates stable square pulses with a 202.3 kHz fundamental repetition rate. When the pump power increases, the pulse duration and output power increase linearly, but the peak power keeps unchanged. The maximum pulse duration is 1.25 μs at the pump power of 540 mW. The maximum average power of output pulses is 3.16 mW, which corresponds to single pulse energy of 15.6 nJ.