Coupling Behaviors of a Radiating Dipole with the Surface Plasmon Induced on a Metal Protrusion.

The coupling behaviors of a radiating dipole with localized surface plasmon (LSP) resonance modes induced on an Ag protrusion in a GaN layer are numerically studied with an algorithm including the feedback effect of LSP resonance to modify the emission behavior of the radiating dipole. Two spectral ranges (400-570 and 570-800 nm) of radiated power enhancement can be observed. The radiated power enhancement in the long-wavelength (short-wavelength) range is generated through the coupling of the radiating dipole with the dipole and quadrupole (higher-order) LSP resonance modes induced on the protrusion. Because the LSP electromagnetic fields of those higher-order modes are mainly distributed around the tip of the protrusion, which is close to the radiating dipole, the radiated power enhancement is quite effective in the blue-green range even though the corresponding metal absorption can be higher than that of a lower-order LSP mode. Compared with the configurations of surface metal nanoparticle (NP) and embedded metal NP, the protrusion structure has the advantages of relatively higher radiated power enhancement in the blue-green spectral range and relatively lower fabrication cost from a practical application viewpoint. [ABSTRACT FROM AUTHOR]