Complex refractive index sensing based on multiple Fano resonance all-dielectric metasurfaces

This study presents a polarization-insensitive all-dielectric metasurface composed of C4 symmetric “□”-shaped silicon units to generate four distinct Fano resonance modes for efficient complex refractive index sensing. The environmental complex refractive index ( N = n -i k ) can be accurately determined by the peak positions and Q factors of the Fano resonances. Specifically, all Fano peaks exhibit linear responses as n varies, with one mode having the highest sensitivity at 260.82 nm/RIU. On the other hand, three of the modes show linear Q- k relationships, of which the highest sensitivity for k reaches 19712.2 RIU -1 . Furthermore, three-dimensional mappings of the peak and Q values vary with n and k values, and are established to measure the complex refractive index of the environment. By simultaneously determining the n and k of the complex refractive index, this method enables precise fingerprint identification of environments.