Bound states in the continuum induced by the strong coupling within the plasmonic lattices

Bound states in the continuum (BICs), manifesting themselves as the collapse of Fano resonance, are observed in many photonic and plasmonic systems. The BICs have been studied systematically through various methods such as the topological photonics analysis, temporal coupled mode theory, multipole decomposition method, and the cavity quantum electrodynamics (CQED) method. Since CQED can give a macroscopic and intrinsic description of light-matter interaction, it is expected to study BIC that participates in strong coupling. What is more, the relation between coupling strength, the Fano parameter, and the asymmetry property of BICs needs to be clarified. In this paper, we investigated the strong coupling between the cavity mode and Bloch-surface plasmon polariton (Bloch-SPP) mode induced by BICs within the plasmonic lattices of the metal-dielectric-metal (MDM) layer. The properties of strong coupling and BIC were revealed theoretically by the quantum model based on the CQED. The increase in the Fano parameters of BICs was proved to facilitate the coupling strength, which was indicated by the monotonically increasing relation between the Fano parameter and the coupling strength. This work may pave the way for flexible modulation and application of BIC in the fields of high-quality plasmonic nanocavity, low-threshold nano-lasers, and quantum information.