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Abstract Pathways towards the generation of extreme optical pulsation in a chaotic transition regime in a linear fibre laser cavity configuration are presented. In a thulium mode-locked fibre laser, extreme events that can be controllably induced by manipulating the cavity birefringence for pulse energies exceeding the single soliton pulse operating regime are studied in detail for the first time. While a solitonic pulsation structure at the fundamental repetition rate is maintained, additional energy is shed in a chaotic manner, leading to broader spectral generation and shorter pulse durations whose behaviour deviates significantly from a classical statistical distribution. These pulses display markedly different characteristics from any previously reported extreme events in fibre lasers associated with multiple solitons and pulse bunching, thus presenting a novel observation of extreme pulsation. Detailed noise studies indicate that significant enhancement of relaxation oscillations, modulation instability and the interplay with reabsorption mechanisms contribute in this transient chaotic regime. The extreme pulsation generated in a compact fibre laser without any additional nonlinear attractors can provide an attractive platform to accelerate the exploration of the underlying physics of the chaos observed in mode-locked laser systems and can lead to novel fibre laser cavity designs. 

We experimentally characterize the dynamics of soliton explosions in a transient chaotic state between a single and double pulsing state, as well as periodic explosions induced by soliton collisions in a dual wavelength soliton state. These explosions occurring in a thulium-doped linear fiber laser with net anomalous dispersion are characterized with real-time measurements based on a modified time-stretched dispersive Fourier transform method relying on second-harmonic generation. 

Real-time explosion dynamics in a transition chaotic state and a dual-wavelength vector soliton state in a thulium-doped linear fiber laser are analyzed with real-time pulse measurements.