High Q-factor multi-Fano resonances in all-dielectric metasurface for high-performance optical switching and sensors

The bound state in the continuum (BIC) in photonics has received widespread attention owing to its ultra-high Q-factors and promise in realizing field enhancement and sensing. In our study, we proposed and studied an all-dielectric metasurface composed of two silicon nano-quadriprisms. By introducing broken symmetry in the nano-structure, the BIC modes were transformed into quasi-BIC modes, resulting in four Fano resonances with limited but extremely high Q-values. Through multipole decompositions and electromagnetic field analysis, we revealed that these resonances were dominated by magnetic dipoles and magnetic quadrupoles responses. The sensing characteristics of the structure were examined, revealing a maximum sensitivity and figure of merit of 383.3 nm/RIU and 958.3RIU −1 , respectively. The structure we proposed achieved dynamic adjustability by changing the polarization angle of incident light, and thus implemented the function of an optical switch. The ON and OFF states of the structure are obtained at y polarization and x polarization, respectively, and the ON/OFF ratio was 29.75 dB. In addition, the phase variations and group indices at the four Fano resonances were analyzed, with the maximum group index reaching 3000. These characteristics make the metasurface suitable for applications in high-performance biosensors, optical switches, and slow-light effects.