On the directivity of optical antennas
Résumé
When coupled to quantum emitters, metallic antennas behave as nanoscale optical resonators and different geometries have been proposed to strongly enhance at a nanometer scale the light-matter interaction. More recently, attention has been focused on the ability of metallic antennas to shape the emission pattern of light emitters, and to redirect the emitted light towards a given direction. Yagi-Uda antennas, patch antennas, bull's eyes antennas, metallo-dielectric antennas are modern designs developped into the optical range of frequencies and that are able to emit light into a narrow angular lobe. In this talk, emphasis will be placed on the fundamental case of a single particle coupled with a single electric dipole emitter. We will detail an analytical model able to accurately describe the collective or reflective property of a particle antenna as a function of the polarisability of the metallic particle as well as the distance between the emitter and the surface of the particle. In particular, we will evidence the fundamental role played by the distance, and we will show that a modification of the emitter/particle distance at a scale around lambda/60 drastically modifies the direction of emission.