Numerical investigation of nonlinear and chaotic dynamics in an erbium-doped fibre ring laser with low frequency cavity-loss modulation

Fibre lasers operating near threshold exhibit high sensitivity to external perturbation due to their intrinsic nonlinear dynamics. However, the dynamical behaviour under modulation is often accompanied by significant fluctuations in the output. The dynamics and bifurcations of erbium-doped fibre ring lasers (EDFRLs) under low frequency cavity-loss modulation (≤15 kHz) show nonlinear behaviour while maintaining traceable periodic patterns. In this work, we numerically investigate the dynamical behaviour and bifurcation structure of an EDFRL. Phase-plane trajectories and return maps are employed to characterise transitions between regimes. For a modulation index of m = 0.13 and relative volumetric pump rate Δ = 150 s −1 , three distinct chaotic regimes are identified. As the modulation frequency increases, the system undergoes a sequence of bifurcations from multi-pulse bursts to single-pulse periodic operation, followed by a period-doubling route to chaos. The overall bifurcations of the peak photon density show a period-doubling route to chaos and stabilise into limit cycles above 10720 Hz. These results provide a systematic characterisation of the nonlinear response of the EDFRL under low-frequency modulation and contribute to the understanding of controlled dynamical regimes in modulated laser systems.