Real-time measurement of soliton-similariton explosions and intermittence instabilities in a mode-locked fibre laser
Résumé
Ultrafast mode-locked lasers are well-known to display a rich variety of unstable dissipative soliton dynamics resulting from the interplay of nonlinearity, dispersion and dissipation. Although laser instabilities have been known and studied in depth for many years, their properties have recently received greatly renewed attention because of the development of time and frequency domain techniques that allow laser dynamics and instabilities to be measured in real-time. This has allowed the variations in circulating pulse characteristics to be examined on a roundtrip to roundtrip basis, providing a new window into understanding these instabilities and how they develop based on the cavity configuration being used. A technique of this kind that has proven both straightforward to implement and powerful is the photonic time stretch or dispersive Fourier transform (DFT) which has been used in a number of important applications including the measurement of soliton rogue waves, modulation instability and supercontinuum noise. The DFT allows direct access to shot-to-shot measurement of the mode-locked fibre laser spectrum and, via computation of the associated autocorrelation function, can also provide complementary time-domain information in cases where multiple pulse states are observed. In this paper, we report results of DFT measurements which have been used to reveal previously unreported behavior in a mode-locked fiber laser designed to operate with soliton-similariton dynamics. In particular, we observe instabilities including soliton explosions, chaotic evolution and oscillation in the relative phase of bound-state multi-pulse molecules, and what we believe to be a previously-unobserved regime of operation associated with the intermittent appearance of short-lived stable single pulses within of otherwise chaotic dynamics. Our results - obtained in a laser believed to be a particularly stable design - suggest that instabilities such as soliton explosions and intermittence are a universal feature of dissipative soliton systems transitioning from noise to stability.