Sub 500 kHz single soliton generation in a ring cavity Er-fiber laser

We report a passive mode-locked fiber laser (PMLFL) in a novel configuration to generate a single soliton with ultra-low repetition rate. The configuration includes a Faraday mirror after the first half of the cavity length to counteract the nonlinear polarization rotation effects. The total cavity length is 428 m including a 400-m SMF-28 fiber which was twisted to cancel the linear birefringence. The strict polarization control establishes a relation between the regimes of generation and the polarization state of the pulses propagating in the cavity. By properly adjusting the initial polarization state, we observed three different emission regimes, the single soliton regime (SR), conventional noise-like pulses (NLP) and noise-like square-waveform pulse (NLSWP). In the SR, we obtain a 2.9 ps pulse duration centered at 1558.7 nm with a 467.2 kHz repetition rate.