Topological edge and interface states in phoxonic crystal cavity chains

Topological states of classic waves are fascinating for both fundamental and practical purposes due to their unprecedented wave characteristics. In this paper, we realize the one-dimensional topological insulators for electromagnetic and mechanical waves simultaneously based on phoxonic crystal (PxC) cavity chains. The proposed PxC cavity chains are the analogs to the Su-Schrieffer-Heeger model in condensed-matter physics. The interaction between the neighboring PxC cavities can be described by the tight-binding model, where the coupling or hopping strength between the adjacent cavities can be tuned by varying their distance. Thus, the PxC cavity chains with topologically nontrivial and trivial phases are achieved by changing the cavity distances directly. The topological edge and interface states for the electromagnetic and elastic (or acoustic) waves are observed simultaneously in the finite-sized PxC cavity chains, which exhibit robustness against geometrical imperfections. The topological states of the proposed PxC cavity chains hold promise for designing robust devices in signal processing, sensing, and optomechanics.