Double Fano resonances based on different mechanisms in a MIM plasmonic system

In this paper, a metal-insulator-metal (MIM) waveguide structure consisting of two identical stub resonators and a rectangular cavity is designed. Two-dimensional finite-difference time-domain (FDTD) method is used to study the performances of the proposed structures. According to the simulation results, the transmission spectrum exhibits two typical sharp Fano peaks. One of them originates from the interaction between the strong trapped resonance in the Fabry-Perot (FP) resonator and the weak resonance in the stub resonators, while the other results from the interference between the narrowband spectrum generated by the rectangular cavity and the broadband spectrum provided by the stub resonators. Based on the different mechanisms, the two Fano resonances can be adjusted independently through changing the parameters of the structure. Besides, multiple Fano peaks are also achieved by adding an extra rectangular cavity. An analytic model based on scattering matrix theory is provided to explain the phenomenon. The results reveal potential applications of the coupled system in the field of sensors.