High figure of merit refractive index sensor with Fano resonance from interference between toroidal dipole and Rayleigh anomaly in asymmetric all dielectric metasurface array

Abstract

Metasurface refractive index sensor has become an important research direction in the field of optical biosensors owing to its capabilities of real time monitoring, compact device size and high sensitivity to the refractive index change of the external environment. During the last decades, the sensitivity of the sensors has been dramatically improved. Improving the figure of merit is another strategy to enhance the sensing performance. In this paper, we propose an asymmetric double semicircular all dielectric metasurface structure. With the interference between excited toroidal dipole and Rayleigh anomaly in the metasurface array, ultra-high figure of merit has been achieved. According to the simulation results, with optimized structure parameters, a Q-factor of 14559 has been obtained with a full width at half maximum (FWHM) of the resonance of 0.06 nm, while the sensitivity is 320 nm/RIU and the figure of merit is 5333 RIU^-1.