High-Q Fano resonance in polymer metasurface for refractive index gas sensing

We propose a polymer metasurface designed on a silicon dioxide substrate, comprised of a periodic array of polymer cylinders with opened ring cavities. Under normal incidence and linearly polarized illumination, the structure supports nine sharp Fano resonances, achieving a maximum quality (Q) factor of 1 × 10⁵. Multipole decomposition and electromagnetic field analysis attribute these resonances primarily to toroidal dipole and magnetic quadrupole modes. As a refractive index gas sensor, the metasurface shows an exceptional sensitivity of 678.57 nm/RIU, an outstanding figure of merit (FOM) of 28274 RIU^-1, and a low limit of detection (LOD) of 1.47 × 10^-6 RIU. These performance metrics highlight its significant potential for multichannel RI gas sensing and environmental monitoring.