Supercavity Modes Excited by Bessel-Type Plasmon Polaritons

High-index dielectric resonators are favorable to enhance light-matter interaction with the advantages of low loss and multipolar resonances. However, realizing a high-Q factor in a single dielectric cavity remains a challenge especially in lossy systems such as that in plasmonics. Here, the resonant modes of a dielectric cylinder excited is explored by bessel-type plasmon polaritons and reveal the general dependence of its eigenfrequency on the physical size. Based on this fundamental a universal and robust approach is proposed to find the high-Q supercavity modes, which arise in the vicinity of the resonance crossing features of two coupled resonant modes in the same radiation channel. Following the proposed principle, one cannot only construct a series of high-Q modes, but also predict their corresponding size parameters and resonant frequencies without relying on the heavy computations of parameter scanning. Such high-Q mode can be easily extended from visible wavelengths to other frequency regime due to scale invariance of the eigenfrequency and the insensitivity of the Q-factor to the permittivity (real part) of the plasmonic substrate. The findings provide guideline for the engineering of high-Q modes and may open up a pathway to design resonant meta-optics devices in lossy dielectric-metal composite system.