High FOM Fano Resonance Refractive-Index Sensor Based on a Baffled MIM Waveguide Coupled with an Inverted L-Shaped Resonator

Abstract A baffled metal-insulator-metal (MIM) waveguide coupled with an L-shaped resonator was developed and a double Fano resonance was excited in the structure. Using the optimal parameters, the sensing characteristics of the structure in a gas environment were studied. The maximum sensitivity was 682 nm/RIU and the maximum figure of merit (FOM) was 7587. Based on this structure, the influence of the resonators on the transmittance characteristics was studied for four different placement ways. A triple Fano resonance was obtained by simply inverting the L-shaped resonator. In this state, the maximum sensitivity and FOM reached 945 nm/RIU and 1.04×105, respectively. Compared with the L-shaped resonator structure, the sensitivity and FOM of the inverted L-shaped resonator structure were significantly improved. This study provides a new concept for designing a refractive-index sensor with high sensitivity, high FOM , and multichannel sensing.