Topological Supercavity Resonances In the Finite System

TL;DR

This paper introduces a new class of topologically robust supercavity resonances in coupled acoustic resonators, achieved through merging bound states in the continuum, with experimental validation and potential applications in sensing and photonics.

Contribution

It presents the theoretical prediction and experimental demonstration of topological supercavity resonances arising from BIC merging in coupled acoustic systems, a novel mechanism for high-Q resonances.

Findings

Demonstrated supercavity modes linked to BIC merging

Experimental confirmation of mode movement, merging, and vanishing

Potential for applications in acoustic sensing and photonics

Abstract

Acoustic resonant cavities play a vital role in modern acoustical systems. They have led to many essential applications for noise control, biomedical ultrasonics, and underwater communications. The ultrahigh quality-factor resonances are highly desired for some applications like high-resolution acoustic sensors and acoustic lasers. Here, we theoretically propose and experimentally demonstrate a new class of supercavity resonances in a coupled acoustic resonators system, arising from the merged bound states in the continuum (BICs) in geometry space. We demonstrate their topological origin by explicitly calculating their topological charges before and after BIC merging, accompanied by charges annihilation. Comparing with other types of BICs, they are robust to the perturbation brought by fabrication imperfection. Moreover, we found that such supercavity modes can be linked with the Friedrich-Wintgen BICs supported by an entire rectangular (cuboid) resonator sandwiched between two rectangular (or circular) waveguides, and thus more supercavity modes are constructed. Then, we fabricate these coupled resonators and experimentally confirm such a unique phenomenon: moving, merging, and vanishing of BICs by measuring their reflection spectra, which show good agreement with the numerical simulation and theoretical prediction of mode evolution. Finally, given the similar wave nature of acoustic and electromagnetic waves, such merged BICs also can be constructed in a coupled photonic resonator system. Our results may find exciting applications in acoustic and photonics, such as enhanced acoustic emission, filtering, and sensing.