In this paper, a novel plasmonic structure consisting of a metal-insulator-metal (MIM) waveguide which is separated in intermediate region coupled with a cross-shaped cavity (CSC) is proposed. Based on the finite element method (FEM), results are simulated by COMSOL Multiphysics software concluding three different Fano resonances peaks and an independent Lorentz peak. Theoretically, multimode interference coupled mode theory (MICMT) is used to calculated the formation of the peaks. Besides, by changing the parameters of the structure, the influence of different parameters on each resonance peak is studied. Based on the original CSC structure, the system is extended to five types of Fano resonance system by appending a semi annular (SA) structure. The research results show that the sensitivity of expanded structure can be up to 1478 nm/RIU, and the FOM value can be as high as 5×105, demonstrating its excellent nano-sensing performance and can be used as an efficient refractive index (RI) sensor.
A plasmonic structure, constituted by metal insulator metal waveguides and split annular cavity connected with rectangular resonator (SACRR), is proposed and investigated. Numerical simulation by the finite element method (FEM) has been done to investigate the transmittance properties of the proposed structure and four Fano resonances arise in the results. To analyze and verify the simulation results, multimode interference coupled mode theory is engaged, theoretically. In addition, the structural parameters are analyzed and discussed to design and control the proposed structure, which shows sufficient flexibility. Due to multi-Fano resonances providing multiple monitoring points and the extremely sharp asymmetry of Fano resonance, the structure can service as a high-performance multichannel refractive index nanosensor with a sensitivity of 1000 nm/RIU and maximum figure of merit of 1.358 × 105. The designed structure can surely meet extensive applications for nanoscale devices and integrated optical devices.
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