Nanoscale Surface Plasmon Polariton Disk Resonators, a Theoretical Analysis

We analyze whispering gallery-type disk resonators with radii down to 50 nm. Single interface waveguiding is accomplished by a plasmonic–dielectric interface operating near the surface plasmon polariton (SPP) resonance, employing a hypothetical material with lower loss than what is currently available in metals or negative permittivity media. The disk is immersed in a second dielectric, nonresonant to the plasmonic medium. Due to the high effective index of the disk mode and the concomitant low radiation losses, the quality ( $Q$ ) values of the resonator are solely determined by material losses, in contrast to more conventional nanoscale resonators. We calculate the dependence of the effective indices of the guided mode, the $Q$ values of absorption and radiation, and the Purcell factor on the deviation from the SPP resonance.