Directional Scattering and Quasi-Bound States in the Continuum in All-Dielectric Nano-Antenna Metasurfaces

Due to their capability to overcome ohmic losses, and the unique ability to manipulate, control and confine electromagnetic waves at the nanoscale dimensions, high index dielectric metastructures have become promising candidates for numerous photonic device applications such as beam steering, imaging, sensing and solar energy harvesting. We numerically study the scattering behavior of an array of silicon nanocylinders, and we show that varying the silicon nanocylinder heights results in the excitation of Fano resonance creating asymmetric scattering spectral profiles. We also demonstrate strong mode coupling behavior called quasi-bound states in the continuum where the modes are localized (trapped) in the nanostructure as a result of suppression of radiative losses leading to a high quality factor due to the disappearance of the width of the Fano lineshape. Our studies also reveal the overlap of the modes between the electric dipole and magnetic dipole moments leading to suppression of light reflectance and transmittance in the metastructure array.