Interaction between single nano-emitter and plasmonic disk–ring nanostructure with multiple Fano resonances

Abstract

We study the emission behavior of an electric dipolar nano-emitter coupled with a disk–ring nanostructure (DRN) that sustains multiple plasmonic Fano resonances. The emitter–DRN electromagnetic coupling efficiency strongly depends on the relative position of the nano-emitter and the DRN, which determines whether the multiple Fano interactions are visibly activated. More specifically, for longitudinal polarization, the multiple Fano resonances are pronounced when the nano-emitter is at the outer apex of the disk or at the gap center of the DRN, observable in the far-field and/or near-field characteristics. However, no obvious Fano feature shows up when the nano-emitter is near the outer apex of the ring. For the case in which the nano-emitter oscillates vertically with respect to the DRN axis, Fano resonance is dramatic only when the nano-emitter is inside the gap of the DRN. We show that the cascading amplification of the dipole moment by the nanodisk is crucial for the excitation of the multiple Fano resonances. Our results are useful in engineering plasmon-modified optical spectroscopy and photon emission control, particularly in resonant plasmonic heterostructures.