Plasmonic band-gap filter by using tapered waveguide

A new design of a plasmonic band-gap filter, based on the metal–insulator–metal structure is proposed and simulated by the finite element method (FEM). Different parts of the filter are laid on a silver substrate which consists of a tapered silicon waveguide and two ring resonators for signal trapping in a predefined range. By using the concept of mode compression in a tapered waveguide and power coupling to peripheral rings, several important results have been found. The filtering action of the structure, between 800–1800 nm, can be tuned by structural parameters engineering, such as waveguide/ring dimensions and indices. Considering a linear relationship between the refractive index and the resonant wavelengths, it was shown that there was a red-shift for various dips when the waveguide and ring indices were increased. The proposed structure has the unique quality of having high amplitudes for the portion of the passed waves and very low amplitudes for the rejected parts. (author)