Numerical analysis of an optical toroidal antenna coupled to a dipolar emitter

We present a quantitative numerical study of the coupling between a single emitter and a gold optical antenna of toroidal shape. We show that the emitter can couple to a variety of surface plasmons localized on the antenna and that these resonances enhance the emissivity and/or the directivity of the radiated power. The properties of the surface plasmon modes and those of the emission strongly depend on the size and aspect ratio of the antenna. We show that the spectral features of small subwavelength toroidal antennas are largely independent from the precise position of the emitter and from the orientation of its dipole moment. These results highlight the great potential of the toroidal geometry for the design of versatile optical antennas that are robust to experimental variability.