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.