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.
Highlights
Mode-locked fibre lasers have attracted significant scientific attention during the past decades as a compact and highly stable platform to explore novel ultrafast phenomena[1,2,3]
Chaotic optical pulsation with controllable levels of the occurrence of extreme events are demonstrated for the first time in a Tm/Ho doped soliton mode-locked linear cavity fibre laser
This study further represents the generation of extreme events in a relatively short linear cavity at a high repetition rate of 135 MHz compared to prior studies which have been exclusively conducted in ring laser cavities, with the highest repetition rate around 17.2 MHz21
Summary
The proposed fibre laser configuration has an energy gap where multi-pulsing states are not supported when the pump power is increased beyond the upper limit of the single-pulsing ML operation. Unique to the studied configuration, the single-pulsing regime does not extend up to a level where sufficient intracavity pulse energy is accumulated for pulse break up into two pulses with energies corresponding to the ML threshold This is shown, which indicates that a minimum of 90 mW of coupled pump power is required to achieve ultrafast pulse formation whereas the allowed upper limit for steady-state solitons within the cavity is 115 mW. The generated ultrafast pulse trains for PC angles of 30° and larger clearly indicate an increased level of chaos and amplitude fluctuations that resemble rogue wave behaviour. This is further supported by the RF domain statistics presented, where the frequency constituents of each wave are decomposed into.
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