A Single-Mode Tunable Plasmonic Filter Based on a Hexagonal Ring Resonator

A plasmonic filter with a novel design has been proposed using an hexagonal ring resonator coupled with two MIM waveguides for the input and output. The basic design yields a two-mode response, which is undesirable for filters. We propose a gap in the two middle sides of the hexagonal ring resonator, which results in a single-mode filter. Additionally, we have implemented sharp-tipped waveguides at the resonator-waveguide connections to improve transmission. This technique leads to a monomode filter at 851 nm, within the wavelength range of 550 nm to 1600 nm. The transmission is 65.5%, with 35 nm of selectivity and a Q-factor of 24.31. The structure uses air as the dielectric and silver as the metal, with silver characterized by the Drude model. The numerical investigations were carried out using the FEM methods implemented in COMSOL Multiphysics software. The favorable filter characteristics suggest strong potential for use in all-optical devices.