Optomechanically induced transparency of topological corner states in phoxonic crystal slabs.

Optomechanical coupling (OM) can induce a narrow optical transparency window, a prominent phenomenon known as optomechanically induced transparency (OMIT). In this Letter, we propose a higher-order topological phoxonic crystal slab to realize robust OMIT. More specifically, we demonstrate the coexistence of photonic and phononic topological corner states with the OM coupling rate reaching 1.336 MHz. This strong interaction renders the system transparent within a very narrow frequency range, even under realistic over-coupled conditions. Since higher-order topological bandgaps protect these corner states, the achieved transparency remains well preserved against structural defects. This contrasts with trivial OMIT mechanisms, which are inherently dependent on the geometry of the optomechanical system. Our work opens a venue for designing what we believe to be novel topological optomechanical devices, which are potentially useful for advanced sensing, filtering, signal processing, and slow light.