Topologically-protected dual-parameter Valley Hall photonic crystal sensor

Topological photonic crystals (TPCs) are considered excellent optical sensor platform due to the robustness of light propagation, immunity to interference, and ease of integration. This paper theoretically proposes a topological valley photonic crystal (VPC) sensor based on second-order corner states and, to our knowledge, realizes for the first time topologically protected dual-parameter detection for refractive index (RI) and temperature. Two highly localized opological corner states (TCSs) are generated by splicing two types of VPCs with broken inversion symmetry. Owing to the very weak coupling between the two TCSs, they respond independently to RI and temperature variations, respectively. Results show that the RI sensitivity is around 653 nm/RIU over a wide range from 1.26 to 1.35, and the temperature sensitivity reaches 235 pm/°C over a broad range from 0 to 100 °C. Fascinatingly, the resonance peak's quality factor (<i>Q</i>) surpasses the order of 10⁵ due to the high localization of TCS. Moreover, the TPC sensor maintains high-performance robustness by deliberately introducing 12 types of defects. This design has great potential in engineering compact, easy-integrated, and dual-parameter sensors in biomedical, chemical, and pharmaceutical fields.