Manipulating the localization of the bound state and electromagnetic field in a plasmonic-dielectric hybrid system

Bound states in the continuum (BICs) have emerged as a powerful strategy for realizing high Q optical resonances, enabling enhanced light–matter interactions in compact nanophotonic systems. Compared to all-dielectric BICs with ultrahigh Q factors, plasmonic nanocavities are promising candidates for light–matter interactions due to their minimal mode volume. Here, we propose and demonstrate a plasmonic-dielectric hybrid (PD-hybrid) metasurface that supports Friedrich–Wintgen BICs (FW-BICs), achieved through coupling between transverse magnetic (TM) and transverse electric (TE) guided-mode resonances (GMRs). Through precise engineering of the Au nanopillars’ geometry, the localization of bound states can be efficiently manipulated in momentum space, with an experimentally observed high Q factor of ∼390 in the visible range. The temporal coupled-mode theory (TCMT) shows that the localization of bound states is mediated by the near-field coupling coefficient between TM and TE modes, which accompanies the electromagnetic field of FW-BICs transitioning from localized resonances to extended nonlocal modes. The proposed hybrid photonic system could offer a promising platform for high Q and field localization nanophotonic devices.