A temporal insight into the rich dynamics of a figure-eight fibre laser in the noise-like pulsing regime

We report on the dynamics of noise-like pulses at the ns scale in a passively mode-locked fibre laser, which grow in complexity as wave retarder adjustments are performed. We can observe that the laser operating in the fundamental mode can be tuned to get different shapes of the noise-like pulse. Following a regime of a very stable waveform, regimes characterized by a much more variable (but still compact) waveform are observed. Then we can get the fragmentation of the main bunch and expulsion of sub-packets and, finally, a variety of puzzling dynamics with increasing complexity are evidenced. Although the collective behaviour of the multiple waveforms is at first sight random we can observe some well-defined patterns in the kinematics of light bunches at the global cavity scale. These results may be useful to unravel the subtle mechanisms at play in complex dissipative nonlinear systems such as passively mode-locked fibre lasers.