Switchable Photon-Plasmon Coupling in a Single-Nanoparticle-Perturbed Microcavity

Single plasmonic nanoparticles coupled to a whispering-gallery-mode (WGM) microcavity provide an excellent platform to explore enhanced light–matter interactions. Here, we demonstrate switchable coupling between localized surface plasmon resonances (LSPRs) and three-dimensionally (3D) confined WGMs in an optoplasmonic system composed of a single gold nanorod and a microtubular cavity. The photon–plasmon coupling is efficiently switched between an “ON” and “OFF” state by tuning the excitation of the LSPR to match or mismatch the WGMs, where spectral match and spatial overlap play crucial roles. This switching phenomenon is indicated by the observations of spectral energy shifts, intensity variations, and spatial redistributions of the 3D confined WGMs. To explain the observed results, a deformed potential well model is introduced based on perturbation theory, where the polarizability and enhanced electric field induced by the single plasmonic nanorod are considered. The present work provides a convenient way to manipulate the photon–plasmon coupling in a hybrid optoplasmonic system, paving the way for controllable light–matter interactions and opening up promising applications in future subwavelength photonic technologies.