Unidirectional broadband radiation of honeycomb plasmonic antenna array

Emerging plasmonic and photovoltaic applications benefit from effective interaction between optical antennas and unidirectional incident light over a wide spectrum. In this study, we propose a honeycomb array of plasmonic nanoantennas with broken symmetry for obtaining a unidirectional radiation pattern over a wide spectrum. The honeycomb nanoantenna array is based on a hexagonal grid with periodically arranged nanostructure building blocks. To analyze the far-field optical distribution and spectral behavior of the plasmonic antenna honeycomb, a two-dimensional Wigner-Seitz unit cell is used to represent the nanostructure building block of broken symmetry. When combined with periodic boundary conditions, superposition of the fields from a single asymmetric building block generate far-zone optical fields lead to constructive or destructive interference in different directions. The constructive interference along the array's normal direction engenders unidirectional radiation. Consequently, due to the broken symmetry of the Wigner-Seitz cell, multiple resonances are supported by the plasmonic antenna honeycomb array over a broad spectrum.