Avoided resonance crossing and non-reciprocal nearly perfect absorption in plasmonic nanodisks with near-field and far-field couplings

Avoided resonance crossings (ARC) in plasmonic nanodisk structures due to near field or far field couplings were numerically demonstrated. Near field coupling in disk dimmer leads to both energy and linewidth anti-crossing as one disk size approach the other. Far field coupling in double layered disk arrays also leads to linewidth anti-crossing but energy crossing of the absorption spectrum illuminated from different sides. We observed the disappearing of Fabry- Perot resonant mode and the nonreciprocal nearly perfect absorption. These phenomena are explained by a Frequency-Selective-Surface-Fabry-Perot model.