Directional Radiation of Surface Plasmon Polaritons at Visible Wavelengths through a Nanohole Dimer Optical Antenna Milled in a Gold Film

Abstract

The mechanism of optical interaction of two nanoholes, milled in an opaque gold film, by means of surface plasmon polariton (SPP) propagation is investigated. The interaction depends on the polarization direction of the incident light when the nanohole pair is illuminated through uniform single antenna excitations. It is shown that by illuminating one of the nanoholes, under single antenna excitation, the other nanohole can be excited indirectly via propagated SPPs from the excited nanohole. In addition, it is found that the spectrum of electromagnetic power above the surface of the metallic film at an arbitrary point along the axis of the nanohole pair presents two resonant peaks. These peaks are due to the optical interaction between nanoholes, where the short-and long-wavelength peaks can be assigned to in-phase and antiphase interactions of magnetic dipoles relative to each nanohole, respectively. The magnetic coupled dipole approximation (MCDA) method confirms the simulation results.

A phased antenna array for surface plasmons

“…To achieve this with a small footprint and with control over directionality, gratings 6 7 8 9 10 and two dimensional hole arrays 11 12 are used. It has been shown that a limited number of well-positioned holes can give directional SPP emission 13 14 15 16 and even one hole 17 already gives a dipolar SPP radiation pattern. Strategies based on patterns of holes in metal films are promising, however they are static in design, resulting in a fixed radiation pattern.…”