Breathing Dissipative Soliton Molecule Switching in a Bidirectional Mode-Locked Fiber Laser

Breathing optical solitons propagating in a dissipative nonlinear system can interact and bind stably, forming an optical soliton molecule that presents striking molecule-like dynamics. To date, the breathing soliton pair has been mainly observed in the microcavity platform, and the peculiar dynamic evolution of breathing soliton molecules (BSMs) remains largely unexplored in modelocked fiber lasers. Herein, the transient switching dynamics of BSMs in a bidirectional ultrafast fiber laser is revealed, specifically triggered at different parameter spaces of saturable absorption with manipulation polarizations that maintain constant pulse separation or undergo strong repulsion and kink after switching. All-optical switching of breather molecules and significantly increasing multiple soliton molecules' switching of two or three solitons between states with different binding separations by applying a strong stimulus with periodic pump modulation is demonstrated. The instantaneous pulse breakup can be induced by the collision of bidirectional breathing solitons in each switching, which is characteristic of the breathing solitons in a bidirectional fiber laser and further corroborated by numerical simulation. The study unveils new perspectives into the ultrafast transient process of BSMs in various dissipative systems.