A deep subwavelength cavity formed by total external reflection of surface plasmon polariton

Abstract

We numerically analyze the characteristics of a nanocavity in surface plasmon polariton (SPP) modes confined by total external reflection (TER) at deep subwavelength scales. This SPP-TER cavity consists of a low-index dielectric channel on a flat metal surface covered by a high-index gain medium. Compared to other types of nanocavities formed by total internal reflection such as a metallic channel and a high-index dielectric channel, an SPP-TER nanocavity provides superior functionality on mode area, confinement factor in the gain medium, Q-factor, and threshold gain. From this result, we suggest the SPP-TER nanocavity as a promising high-quality deep-subwavelength scale resonator, which is an essential ingredient in nanophotonics.