Collective explosive dynamics of soliton rains in a figure-8 Tm-doped fiber laser

We report the explosive events of unidirectional and bidirectional soliton rains (SRs) in a Tm-doped fiber laser mode locked by the nonlinear amplifying loop mirror technology. It is observed that the explosive evolution undergoes a disintegrating process from a multi-SR state to a normal SR, and to a soliton group followed by annihilation, and eventually to the explosion. Continuous observations reveal that each explosion exhibits a decay, a sudden drop, and an eruption of energy, thereby manifesting a quasiperiodic characteristic. A numerical experiment has effectively simulated the explosive processes and confirmed the $Q$-switching effect inside the collective soliton explosions. An analysis of the orbit diagrams derived from nonlinear mapping solidly substantiates the origin of the SR explosions: a gain-modulated mode-locking mechanism. These findings unveil an extreme collective soliton behavior in dissipative systems.