Plasmonic bandpass filters with cascaded rectangular ring resonators.

We theoretically present the analysis and design of a nanoplasmonic bandpass filter with flat-top spectral characteristics by cascading a series of directly connected rectangular ring resonators based on metal-insulator-metal waveguides. Analyzed by the equivalent lumped circuit model of the transmission line to plasmonic waveguides, the transmission properties of a symmetric rectangular ring resonator with the directly connected input and output waveguides are approximately the same as that of a Fabry-Perot resonator. Then the thin-film design methodology is applied to realize a plasmonic bandpass filter with the squared passband. An example of cascaded two-rectangular ring resonator structure is numerically demonstrated by using the transmission line model and 2D finite difference time domain method.