Employing Topological Properties of Phase Singularities for Designing Supercavity Systems with Tailored Excitation

Abstract

AbstractTrapping electromagnetic waves in high‐index resonators with extreme quality factors (Q‐factor) can be achieved by exciting supercavity (quasi‐bound states in the continuum, quasi‐BIC) modes with minimal radiation loss. Conventionally, the quasi‐BICs are achieved by tuning the resonator dimensions to promote destructive interference between two modes in the cavity. In this work, an enhanced Q‐factor is achieved by manipulating the structure of a near‐field excitation source and tailoring the excitation strength of individual multipolar modes. A pair of concentric rings with strong mutual coupling is used in contrast to a simple single‐ring case. We show that adding the second passive ring enables additional degrees of freedom to manipulate the multipolar content exited in the cavity. The multipole decomposition of the cavity modes is performed using full‐wave numerical simulations to support these claims. Experimental validation with a double‐ring fed supercavity demonstrates the highest measured Q‐factor of ≈310 or ≈2× the quality factor of a design without supercavity, which is consistent with a numerical model predicting up to 3× enhanced Q‐factor. We show that, analyses of polarization singularities and multipolar decomposition can be used to understand, characterize, and design such systems, employing their topological properties not broadly explored before.