The interplay of nonlinearity and topology–nontrivial eigenmodes coupling induced by nonlinearity

Trivial and nontrivial photonic SSH lattices are established by direct cw-laser writing in a bulk nonlinear crystal and thereby the nonlinearity-induced coupling of light into topological edge and interface states is experimentally demonstrated. A general theoretical framework is developed for interpreting the mode-coupling dynamics in nonlinear topological systems. This protocol is also applicable to systems other than SSH lattices and even to systems beyond the photonic platform.