Coherent energy transfers between orthogonal modes of a dielectric cavity bridged by a plasmonic antenna

Here, we demonstrate a strategy that two orthogonal modes in a dielectric cavity can efficiently couple with each other through the bridging effect of a plasmonic antenna. In such a dielectric-antenna hybrid system, a plasmonic antenna can coherently interact with both modes of the dielectric cavity, which brings sufficient coherent energy transfers between the two orthogonal modes. Specifically, a broad electromagnetic mode and a narrow whispering gallery mode (WGM) in a subwavelength silicon disk are considered, where they cannot directly interact with each other through near-field couplings. By introducing a plasmonic antenna, coherent energy transfer between the above two modes occurs, which is confirmed by both far-field spectra and near-field distributions. More investigations show that spectral and spatial overlaps between the involved modes can largely affect energy transfer behaviors. Those overlaps are highly dependent on various parameters of the system. The WGM response in the hybrid system can even exceed that of an individual disk. Our proposed strategy can be extended to other similar systems and the modified optical responses can find applications in enhanced light-matter interactions.