All-Dielectric Metasurface for Achieving Perfect Reflection at Visible Wavelengths

Metamaterials have attracted considerable attention owing to their extraordinary ability in controlling the propagation of electromagnetic waves. These materials can be realized using artificial composites consisting of subwavelength metallic resonators, but losses of the metallic components may significantly degrade the performance of metamaterials, especially in the visible region. Here, we propose low-loss all-dielectric metasurfaces, comprised of a monolayer of titanium dioxide (TiO2) nanoparticles, to achieve perfect reflection band at visible wavelengths. Using the Mie scattering theory, we explore the electromagnetic scattering features of one single TiO2 nanosphere and show that both electric and magnetic dipole resonances can be excited inside the sphere in the visible range. Then, a semi-infinite medium of TiO2 nanospheres is studied using Lewin effective-medium model, and we find that the effective permeability or permittivity becomes negative around the magnetic or electric resonance wavelength, leading to the perfect reflection of light. On the basis of these results, we design a monolayer of TiO2 nanocylinder array to achieve a flat-top perfect reflection band by optimizing the wavelength interval between the magnetic and electric resonances. In addition, it is shown that the position of the perfect reflection band can be adjusted across the whole visible spectrum by changing the dimensions and lattice period of the TiO2 nanocylinder array. Our design of all-dielectric metamaterial reflectors may find applications in diverse fields such as filter, color printing, spectroscopy, and so on.