Nonlinear Imaging of Nanoscale Topological Corner States

Topological states of light represent counter-intuitive optical modes localized at boundaries of finite-size optical structures that originate from the properties of the bulk. Being defined by bulk properties, such boundary states are insensitive to certain types of perturbations, thus naturally enhancing robustness of photonic circuitries. Conventionally, the N-dimensional bulk modes correspond to (N - 1)-dimensional boundary states. The higher-order bulk-boundary correspondence relates N-dimensional bulk to boundary states with dimensionality reduced by more than 1. A special interest lies in miniaturization of such higher-order topological states to the nanoscale. Here, we realize nanoscale topological corner states in metasurfaces with C-6-symmetric honeycomb lattices. We directly observe nanoscale topology-empowered edge and corner localizations of light and enhancement of light-matter interactions via a nonlinear imaging technique. Control of light at the nanoscale empowered by topology may facilitate miniaturization and on-chip integration of classical and quantum photonic devices.

Automated summary

Topological states of light localized at the boundaries of finite-size optical structures, originating from bulk properties, exhibit insensitivity to perturbations and enhance the robustness of photonic circuitries. The higher-order bulk-boundary correspondence relating higher-dimensional bulk states to lower-dimensional boundary states is of interest for miniaturization to the nanoscale. Nanoscale topological corner states in metasurfaces allow for enhanced light-matter interactions, potentially facilitating the miniaturization and integration of classical and quantum photonic devices on-chip.