Multi-Fano Resonances in Graphene Coated All-Dielectric Metasurface for Refractive Index Sensing With High Figure of Merits

At present, many refractive index sensors based on plasmonic structures are inefficiency in practical applications due to the presence of metal ohmic losses. Here we propose an all-dielectric metasurface and conduct a comprehensive analysis of the multi-Fano resonances in the structure with high Figure of Merit for the near-infrared regime. The structure is composed of two silicon elliptical cylinders with asymmetric minor axe on silica substrate coated graphene. The finite-difference time-domain method for three-dimensional model is utilized for investigating the transmission spectra and electromagnetic field distributions. The results show the Fano resonances are arising from the interactions between a radiant mode and a non-radiative dark mode by adding asymmetric parameter. Four sharp Fano peaks can be observed which the maximum Q-factor can exceed 10 ⁴ . According to the electromagnetic field distributions, we analyze the resonant modes of the four peaks in detail and investigate the influence of geometry parameters on the resonances. Furthermore, we find that the Fano resonances are very sensitive to the background refractive index. The results show that the sensitivity of the structure can achieve 400 nm/RIU and the corresponding figure of merit can reach 3074. The proposed structure has potential application as refractive index sensor.