Multiple fano resonances in a coupled plasmonic resonator system

A refractive index sensor based on metal-insulator-metal waveguides coupled with two rectangular cavities is proposed and investigated by using a finite-difference time-domain method and coupled mode theory. The calculation results show that dual Fano resonances can be manipulated independently through adjusting the parameters of the system due to the local discrete states caused by different cavities. Moreover, the line shape of the transmission spectrum can be tuned by changing the height of the output port. In addition, triple Fano resonances with considerable performances are also achieved after adding an extra slot cavity, and the sensitivity of up to 985 nm/RIU and the figure of merit of up to 54 are obtained. It is believed that the proposed structure can find wide applications in sensors, nonlinear devices, and slow-light devices.