Phase effects on the optical near-filed interaction of a nanohole dimer milled in a gold film

The near-field optical interaction of a nanohole dimer milled in a gold film and illuminated by an optical plane-wave is investigated. Depending on the polarization direction of the incident light, two resonant peaks are generated, in the normalized transmission spectrum due to the strong interaction between the nanoholes. In order to elucidate the nature of the interaction between the nanohole dimer elements at the resonant peaks, the symmetry breaking idea is applied. It is found that, in contrast to the complementary metallic nanoparticle dimers, the short and long wavelength peaks of the transmission spectrum can be assigned to in-phase and out-of-phase interaction of two adjacent magnetic dipoles, respectively. Furthermore, it is shown that breaking the symmetry in line with the polarization of the incident magnetic field results in severely antiphase interaction, while breaking the symmetry in line with the polarization of the incident electric field results in slightly out-of-phase interaction, at the long wavelength peak. The numerical simulation results are verified with Magnetic Coupled Dipole Approximation (MCDA) method.