Real-Time Observation of the Regime Transition Dynamics of Mode-Locked Fiber Lasers

Mode-locked lasers exhibit complex nonlinear dynamics. Precise observation of these dynamics will aid in the understanding of the underlying physics and provide new insights for laser design and applications. The starting dynamics, from initial noise fluctuations to the mode-locking regime, have previously been observed directly by time-stretched transform-based real-time spectroscopy. However, the regime transition dynamics, which are essential processes in mode-locked lasers, have not yet been resolved because regime transition process tracking is very challenging. Here we demonstrate the real-time observation of the regime transition dynamics enabled by our design of a real-time programmable mode-locked fiber laser, in which different operating regimes can be achieved and switched automatically. The regime transition dynamics among initial noise fluctuations, Q-switching, fundamental mode-locking and harmonic mode-locking regimes have been observed and thoroughly analyzed by both temporal and spectral means. These findings enrich our understanding of the complex dynamics inside mode-locked lasers.