Optical Interaction of a Pair of Nanoholes in Au Film via Surface Plasmon Polaritons

The optical interaction mechanism of a nanohole pair milled in an opaque gold film by means of surface plasmon polaritons (SPPs) propagation is investigated. This interaction depends on the polarization direction of the incident light and the separation distance between the nanoholes. It is found that when the nanoholes are illuminated by a plane wave incident light polarized parallel to the axis of the nanohole pair, the SPP waves can propagate between the nanoholes, and therefore, the nanoholes can interact through SPPs. In contrast, it is shown that for the incident plane wave polarized perpendicular to the pair axis, the propagation direction of the SPPs is normal to the pair axis, and thus, a weak interaction through the SPPs can occur between the nanoholes. It is also shown that in order to investigate the interaction of the nanoholes through the SPP waves, each nanohole can be modeled by a magnetic dipole, which propagates SPPs. Thus, the optical properties of the interacting nanoholes can be modeled using a magnetic-coupled dipole approximation method accounting SPPs to confirm the simulation results.