Performance analysis and optimization of high Q-factor toroidal resonance refractive index sensor based on all-dielectric metasurface

Sensing is a crucial step to provide information for biology and chemistry. The introduction of a new method with high sensitivity, robustness and low cost has been a research hotspot recently. In this paper, we propose a split ring metasurface composed of silicon nanorods, which shows ultra-high local field enhancement in the near infrared band. Further, the enhanced toroidal dipole is confirmed by multipole decomposition and surface current distribution. Then, the parameter adjustment and sensing performance are analyzed and calculated, and the obtained sensitivity and figure of merit (FOM) are 430 nm/RIU and 1720 RIU-1 respectively. In order to improve the sensing performance, three different substrate etching schemes are proposed, in which the maximum sensitivity and FOM values are 500.75 nm/RIU and 3013.33 RIU-1 respectively. Lastly, the effects of material loss, substrate and array effect on Fano resonance are analyzed. The proposed scheme may provide a new idea for the design and optimization of high-performance refractive index sensor.