Tunable Topological Phase Transition in Interacting Soliton Lattices

Topological photonics is nowadays one of the most active areas in optics, yet thus far research efforts in this area are mainly focused on investigating linear topological photonic structures [1] , where dynamics are usually described through eigenmode expansions. The presence of nonlinearity typically couples the eigenmodes and gives rise to nonlinear phenomena ranging from solitons to extreme waves and chaos. Recently, there has been a surge of interest in nonlinear topological photonics, demonstrating that nonlinearity can induce topological phase transitions, coupling into topologically protected edge states, as well as nontrivial topological gap solitons and topological insulators [2] - [7] . However, how nonlinearity affects nontrivial topological systems and couples eigenmodes in nonlinear topological systems still remains a largely unexplored territory. Here, we report dynamical topological phase transitions entirely driven by nonlinearity, achieved in colliding soliton lattices. By forming two one-dimensional soliton sublattices and kicking them initially in opposite directions, soliton interaction forms a paradigm model of topological physics, namely, the Su-Schrieffer-Heeger (SSH) lattice [8] - [10] . During nonlinear propagation, such a soliton SSH-like lattice repetitively evolves from a topological trivial to a nontrivial regime (featured by the Zak phase [8] ), exhibiting dynamical topological phase transitions.