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. The general fundamentals of the optical resonance are elucidated in a single dielectric cylinder excited by bessel‐type plasmon polaritons instead of the free‐space waves. A general design principle is proposed to construct and predict a series of supercavity modes, which may provide guideline for achieving high Q‐factor in lossy system.