Enhancing second-harmonic generation around exceptional points by coupling a quasibound state in the continuum and toroidal dipole modes
Phys. Rev. A 113, 053510 – Published 7 May, 2026
DOI: https://doi.org/10.1103/z6s7-xrw8
Abstract
In optical non-Hermitian systems, exceptional points (EPs) are singularities in the parameter space where at least two eigenvalues and their eigenmodes coalesce simultaneously. Recently, research on the interaction between EPs and bound states in the continuum (BICs) has attracted considerable attention. However, coupling a BIC with leaky Mie resonant modes to form an EP has not yet been explored. Here, we propose coupling a BIC) and toroidal dipole modes to form an EP. By controlling the relative position between the two modes, the BIC is converted into a quasi-BIC while adjusting the coupling strength. Simulations show that the resulting EP exhibits stronger field enhancement and boosts second-harmonic conversion efficiency (CE) by approximately 5.6 times compared to only the toroidal dipole mode alone. Furthermore, unlike quasi-BICs, which require precise control over structural defects, the CE of the proposed model can be further enhanced to 0.35 by structural perturbations. Our research enriches the configurations of EPs and paves the way for their application in high-efficiency harmonic generation.
