Study on Fano resonance sensing characteristics of double-baffle MDM waveguide coupled disk cavity with absorption material

A metal-dielectric-metal (MDM) waveguide coupled disk cavity structure with bimetallic baffle is proposed, which bases on the transmission characteristics of surface plasmon polaritons (SPPs) in subwavelength structure, and the absorption material InGaAsP is filled in the Fabry-Perot (F-P) cavity and disk cavity. The Fano resonance is an asymmetric spectral line formed by the destructive interference between the wide continuous state generated by the F-P resonator and the narrow discrete state interference generated by the disk cavity. Based on the coupled mode theory, the formation mechanism of the Fano resonance of the structure is qualitatively analyzed. The structure was simulated by finite element method to quantitatively analyze the influence of structural parameters and absorption material InGaAsP on the refractive index sensing characteristics. The proposed sensor yields sensitivity higher than 1360 nm/refractive index unit (RIU) and a figure of merit of 4.98 x 105 by optimizing the geometry parameters and filling the absorption material InGaAsP. This structure has potential applications for high integration of nanosensors, slow-light devices, and nano-optical switches.