Graphene Absorption Enhanced by Quasi‐Bound‐State‐in‐Continuum in Long‐Wavelength Plasmonic–Photonic System

Abstract Graphene plasmonic structures can support enhanced and localized light–mater interactions within extremely small mode volumes. However, the external quantum efficiency of resulting devices is fundamentally limited by material scattering radiation loss. Here, such loss channels are suppressed tailoring structure to a symmetry‐protected bound‐state‐in‐the‐continuum (BIC) system. With practical rates doping level in graphene, over 90% absorption near critical coupling expected from numerical simulation. Experimentally measured peak 68% achieved tailored graphene photonic–plasmonic system, with maximum 50% contrast control sample without graphene. Significant reduction plasmon for different spacer thickness verifies sensitivity system quasi‐BIC condition.