Dual-band unidirectional forward scattering with all-dielectric hollow nanodisk in the visible.

High-index dielectric nanoantennas have become an emerging branch of optical nanoantennas, essentially due to their low loss. These types of nanoantennas can achieve both forward and backward unidirectional scattering, enabled by electric dipole and magnetic dipole interaction. Here, we show that the scattering directionality can be further enhanced if higher-order moments are properly balanced and reach the generalized Kerker condition at two different wavelengths in an all-dielectric hollow nanodisk. Moreover, putting the nanodisks in an array of transverse configuration can enhance the unidirectionality to be needle-like, with the main lobe angular beam width α<15°. Finally, we show that such unidirectional radiation properties can be maintained for a local electric dipole source.