Light control based on unidirectional scattering in metal-dielectric core-shell nanoparticles

We theoretically investigate the light control performances of metal−low-permittivity (LP)−high-permittivity (HP) core-shell nanoparticles (M-LP-HP CSNPs). We demonstrate that a free-standing M-LP-HP CSNP can simultaneously possess the zero-backward (ZB) and near-zero-forward (NZF) scattering at different wavelength ranges due to the interference of electric and magnetic modes. We show that at the wavelength of the ZB and NZF scattering, the ability of CSNPs to confine the optical fields within the cavity is quite robust against the existence of LP substrates. As a result, such unidirectional scattering properties are well maintained when the CSNP is placed on the LP substrate. Furthermore, we demonstrate that in the arrays of CSNPs, the high reflection and transmission can be achieved near the wavelengths of NZF and ZB scattering. Particularly for the case of the optimal inter-particle distance, the reflectance can reach 98% over a wavelength range from 868 nm to 935 nm. These features are further tuned to other wavelengths by varying the structural parameters of the CSNPs.