Exploring the Optical Bound State in the Continuum in a Dielectric Grating Coupled Plasmonic Hybrid System

The bound state in the continuum (BIC) explores the extraordinary optical properties of a system possessing wave characteristics that gained recent importance for practical applications, including lasing, sensing, optical tweezing, nonlinear interactions, and many more. Unlike a pure optical or plasmonic system, a hybrid architecture with coupled photonic–plasmonic characteristics can offer the intermittent resonant modes for suitable applications. Therefore, BIC modes are investigated here in such a photonic–plasmonic hybrid structure made up of a dielectric sinusoidal grating deposited on a flat metal layer via low‐cost fabrication methods. Such a design has not been subjected to the investigation of BIC formation so far. The structure‐supported resonant modes are numerically studied by analyzing the reflection characteristics in the parametric space. The Friedrich–Wintgen bound state (FW‐BIC) is produced by the interference of distinct resonance channels, further resulting in a quasi‐BIC hybrid mode revealed in the parametric sweep. An additional angular scan demonstrates the intrinsic symmetry‐protected BIC (SP‐BIC), and its hybridization with a plasmonic mode results in a distinct FW‐BIC mode and a quasi‐BIC hybrid mode. The experimentally obtained spectral characteristics in the angular resolved scan between 5 to 20 degrees verify the quasi‐BIC hybrid modes with good quality factors and enhanced field confinement. Dielectric grating coupled hybrid plasmonic system is investigated for bound state in the continuum (BIC) modes. BICs originated by the resonance synergies between a photonic grating and a plasmonic thin film are explored to full depths. Identified BICs in both theoretical and experimental observations can be useful in attaining high quality factors for nanophotonic device applications.