Collective soliton collision annihilation and related collisional statistics in a figure-8 Tm-doped fiber laser

We report an unusual collision-induced collective annihilation of solitons at 2 $\textmu{}\mathrm{m}$ in a figure-8 Tm-doped fiber laser. The solitons are generated in a unique bidirectional soliton rain state, where the interaction of heterogeneous vector solitons stimulates deep inelastic collisions. The experiment shows that the solitons activate four collisional scenarios and eventually are annihilated after an average of three to four collisions, adhering to a geometric distribution. The collision-annihilation state can be maintained even for certain energy perturbations, unveiling an extreme soliton characteristic in a large anomalous-dispersion regime.