Multi-GHz repetition-rate pulse generation by gain instability in a semiconductor-based all-fiber laser

We present a novel, simple and highly effective method for generating multi-GHz regular pulse trains in lasers. This method relies on self-sustaining cross-gain modulation achieved by incorporating negative optical feedback (NOF) into a cavity equipped with a semiconductor optical amplifier (SOA). Notably, this approach not only facilitates pulse formation without the need for active modulation or saturable absorption but also enables effortless multiplexing of the laser system to achieve diverse pulse repetition rates. The feasibility of the method was confirmed by the stable generation of sub-nanosecond pulses at $1.35 \mathrm{GHz}, 1.57 \mathrm{GHz}$, and 1.79 GHz repetition rates in an SOA-based laser with a simple ring all-fiber all-PM cavity.