Enhancing Plasmonic–Photonic Hybrid Cavity Modes by Coupling of Individual Plasmonic Nanoparticles

We report the multibody coupling behavior of a vertical hybrid plasmonic–photonic cavity whose output mode can be selected by different lateral geometrical configurations of plasmonic nanostructures for a novel compact optical modulation strategy. The hybrid cavity has a Fabry–Pérot-based configuration with a SiO2/Si dielectric interface at one end and plasmonic individual or coupled Au nanospheres (AuNSs) on the other end. The AuNS acts as an optical antenna that outcouples the standing wave inside the cavity to the far-field. The behavior of this hybrid antenna can be altered by the lateral near-field coupling of two AuNSs, allowing different output mode to be amplified. Upon assembly, the plasmonic peaks of the AuNSs are discretized by the photonic cavity, forming hybrid modes that are distinctively different from the original Fabry–Pérot modes. A different primary mode can be selected according to the spectral envelope imposed by the plasmonic oscillation from respective AuNS nanostructures. Optical responses from monomer and dimer are recorded at single-particle resolution, and their interactions with a photonic cavity are analyzed using subnanometer grid finite difference time domain (FDTD) simulations to reveal the underlying multibody coupling mechanism. We also demonstrate the potential for the hybrid microcavities to incorporate gain media for potential applications in photonic circuits and near-field spectroscopy.