Ultrahigh-Quality-Factor Topological Photonic Crystal Refractive Index Sensor Based on Second-Order Corner State

Owing to the flexible light control and the immunity to defects and impurities, topological photonic crystals (TPC) are considered an excellent platform in the engineering of optoelectronic devices. Herein, four TPC refractive index (RI) sensors are theoretically proposed based on the su-Schrieffer-Heeger (SSH) model. Zero-dimensional topological corner states (TCS) and 1-D topological edge states (TES) are demonstrated by the band structure and the Zak phases. Four TPC sensors are based on single topological microcavity (TCS formed by two TES and four TES), trivial corner states (TRCS)-TES coupling, and TCS-TES coupling. The TCS-based TPC sensors exhibit an ultrahigh quality factor (Q) of$\gt 10^{{6}}$. Moreover, TPC sensor based on TCS-TES coupling remain a topological robustness with >99.4% sensitivity quality of reproduction by artificially introducing eight-type defects. Notably, the design based on TCS-TES coupling presents a sensitivity of 413.76 nm/RIU and a Q value of$2.8\times 10^{{6}}$in a broad RI range of 1.00–1.50. This work not only provides a new way of 2-D photonic crystals (PC) sensor applications but also offers a guidance for the design of TPC sensors.