Nonhermiticity-induced higher-order topological insulator in fractal-like photonic lattices

We experimentally realize nonhermiticity-induced higher-order topological insulators in fractal-like photonic lattices with first-generation Sierpinski gaskets serving as unit cells. By introducing controllable optical loss into specific waveguides, we demonstrate that nonhermiticity can drive the system from a trivial phase to a nontrivial topological phase, enabling the emergence of corner and edge states. We fabricate the tailored photonic lattices via femtosecond laser direct writing and experimentally observe the loss-induced localization of edge and corner modes. This work not only expands the scope of topological photonic materials, but also opens up new opportunities for the development of reconfigurable topological photonic devices.