Coherent Control of Topological States in an Integrated Waveguide Lattice

Topological photonics holds the promise for enhanced robustness of light localization and propagation enabled by the global symmetries of the system. While traditional designs of topological structures rely on lattice symmetries, there is an alternative strategy based on accidentally degenerate modes of the individual meta-atoms. Using this concept, we experimentally realize topological edge state in an array of silicon nanostructured waveguides, each hosting a pair of degenerate modes at telecom wavelengths. Exploiting the hybrid nature of the topological mode, we implement its coherent control by adjusting the phase between the degenerate modes and demonstrating selective excitation of bulk or edge states. The resulting field distribution is imaged via third harmonic generation showing the localization of topological modes as a function of the relative phase of the excitations. Our results highlight the impact of engineered accidental degeneracies on the formation of topological phases, extending the opportunities stemming from topological nanophotonic systems.

Automated summary

Topological photonics utilizes global symmetries of the system to enhance the stability of light localization and propagation. In addition to traditional lattice symmetries, an alternative strategy based on accidentally degenerate modes of individual meta-atoms exists. In this study, we experimentally realize a topological edge state in an array of silicon nanostructured waveguides, each having a pair of degenerate modes at telecom wavelengths. By exploiting the hybrid nature of the topological mode, we demonstrate coherent control through the adjustment of phase between the degenerate modes, selectively exciting bulk or edge states. Third harmonic generation imaging confirms the localization of topological modes as a function of relative phase excitations. The engineered accidental degeneracies in our study highlight their impact on the formation of topological phases, expanding the possibilities in topological nanophotonic systems.