Silver Nanocap Enabled Conversion and Tuning of Hybrid Photon-Plasmon Modes in Microtubular Cavities

Hybrid photon plasmon modes are promising for the study of enhanced light matter interactions due to the formation of a unique plasmon-type evanescent field. Here, we demonstrate the tunability of photon plasmon coupling enabled by a metal nanocap on a microtubular cavity. An angle-dependent tuning of the photon plasmon hybridization is revealed, where the dominant polarization is transverse magnetic (TM) polarized at the middle-top of the nanocap and gradually converts to be transverse-electric (TE) polarized at the sidewall of the microtube cavity. The intensity ratio of strongly hybridized TM and TE modes is extremely sensitive to nanoperturbations at the metal nanocap, thus providing a novel scheme for surface sensing. Theoretical calculations show that the sensitive intensity ratio change originates from the distinct tuning effect on the TM- and TE-polarized hybrid modes, which is particularly significant in thin-walled microtubular cavities. Our work reports photon plasmon modes tuned by a metal nanostructure, which are promising for the fundamental studies of enhanced light matter interactions and relevant applications.