Topological Floquet interface states in optical fibre loops

We experimentally observe a coexisting pair of topological anomalous Floquet interface states in a (1+1)-dimensional Discrete Photon Walk. We explicitly verify the robustness of these states against local static perturbations respecting chiral symmetry of the system, as well as their vulnerability against non-stationary perturbations. The walk is implemented based on pulses propagating in a pair of coupled fibre loops of dissimilar lengths with dynamically variable mutual coupling. The topological interface is created via phase modulation in one of the loops, which allows for an anomalous Floquet topological transition at the interface.