High-performance refractive index sensing system based on multiple Fano resonances in polarization-insensitive...

An optical refractive index sensor is a detection device that can convert changes in the refractive index into detectable optical information. The combination of surface plasmon resonance (SPR) and Fano resonance can improve some key indicators, i. e., sensing sensitivity, figure of merit (FOM), band number, and polarization sensitivity, which are all related to the comprehensive performance for high-precision and multi-band sensing. In our manuscript, we proposed a refractive index sensor composed of a nanoring array and a Fabry-Pérot (F-P) resonant cavity. The coupling of the localized surface plasmon resonances (LSPR) of the nanoring array and the cavity mode of the F-P resonant cavity can produce double Fano resonances. The corresponding sensing sensitivities can reach 621.5 nm/RIU and 906.9 nm/RIU, and the corresponding FOMs can reach 119.7 and 119.0. Then we studied the influence of the structure parameters on the sensitivity and FOM of the sensor through simulation calculation and theoretical analysis and verified the insensitivity of the structure to the polarization of incident light. Our structure has high comprehensive performance, not only polarization insensitivity but also high sensing sensitivity and FOM in both bands, which is more suitable for practical applications.