Designing scalable single-mode to seven-mode plasmonic filters utilizing disk and ring-shaped resonators

In this paper, seven surface plasmon-based filters using a single disk resonator (DR) and a DR coupled with one to six ring-shaped resonators (RSRs) are proposed. In these configurations, the resonators are bidirectionally connected to a pair of metal–insulator-metal (MIM) waveguides. The initial filter structure, consisting of only a single DR, functions as a single-mode band-pass filter. By coupling a disk resonator with a ring-shaped resonator (RSR), a dual-mode filter is created. Following this pattern, each additional RSR introduce another mode to the transmission spectrum. Essentially, the innovative method detailed in this work allows for the creation of plasmonic filters capable of operating with one through seven distinct modes. By utilizing a consistent topology, the results for various structural geometries with different numbers of RSRs are achieved, showcasing true scalability. Moreover, the quality factor (Q-factor) of the resulting modes is enhanced by increasing the quantity of RSRs. Consequently, these filters detailed in this study are suitable as foundational designs for optical sensors that require varying levels of sensitivity. The insulator material employed is air, while silver, whose properties are described by the Drude model, is used as the metal. Every result was generated through the finite-difference time-domain method, a technique known for its numerical stability and minimal dispersion error. Due to the remarkable features such as single and multi-mode filtering, tunable resonant frequency, and variable Q-factor, the filter topologies proposed here can find applications in more complex designs, including optical sensors, demultiplexers, splitters, couplers, and so on.