Multiple Fano resonances by MIM waveguide coupling whispering gallery mode resonator and application in Refractive index sensing

Abstract

In this study, a baffled metal – insulator – metal (MIM) waveguide coupled with a whispering gallery mode resonator (WGMR) is proposed. This structure could excite quadruple Fano resonances. The asymmetric Fano resonance transmittance spectrum and the electric field at the resonance peak were numerically simulated using the finite difference time domain method. The obtained data were fitted using the multimode interference coupled mode theory. The number of Fano resonance peaks was tuned by the outer radius of the WGMR. With other geometric parameters unchanged, the number of Fano resonance peaks increased with increasing outer radius of the WGMR. When the ring width was fixed, the structure could excite multiple Fano resonances within a certain outer radius range. This structure was used for refractive index sensing and its sensitivity and figure of merit (FOM) were 3004 nm/RIU and 3.14× 104 in a gas environment, respectively. Therefore, the proposed structure can excite multiple Fano resonances and achieve a high sensitivity and FOM, providing a theoretical basis for micro and nano applications.