Effects of Surface Plasmon Coupling on the Whispering-Gallery Resonance in a Hexagonal Nanowire Cavity Structure

The effects of surface plasmon (SP) coupling with the excitation radiating dipole on the behaviors of the whispering-gallery resonance (WGR) modes in a hexagonal GaN nanowire cavity structure, either suspended or supported by a substrate, are numerically investigated by placing an Ag nanoparticle (NP) on one of six facets of the hexagonal structure. Through the Purcell effect, the intrinsic resonance behavior of a WGR mode can affect the radiation behavior of the source dipole and hence influence the SP-coupling behavior, which eventually determines the effects of SP coupling on the WGR behavior. The SP coupling can produce two competing effects, including the enhanced stored energy within the resonance cavity and the increased light extraction from the cavity into the air. Both of them are related to the Purcell factor and quality- (Q-) factor of cavity resonance. When the former (latter) dominates, the resonance intensity of a WGR mode can be enhanced (suppressed). It is observed that the WGR becomes stronger, i.e., the radiated power is enhanced, through SP coupling when the intrinsic resonance is not strong. The resonance intensities of those WGR modes with strong intrinsic resonances or high Q-factors can be reduced.