Toward Perfect Optical Diffusers: Dielectric Huygens' Metasurfaces with Critical Positional Disorder.

Conventional optical diffusers, such as thick volume scatterers (Rayleigh scattering) or microstructured surface scatterers (geometric scattering), lack the potential for on-chip integration and are thus incompatible with next-generation photonic devices. Dielectric Huygens' metasurfaces, on the other hand, consist of 2D arrangements of resonant dielectric nanoparticles and therefore constitute a promising material platform for ultrathin and highly efficient photonic devices. When the nanoparticles are arranged in a random but statistically specific fashion, diffusers with exceptional properties are expected to come within reach. This work explores how dielectric Huygens' metasurfaces can implement wavelength-selective diffusers with negligible absorption losses and nearly Lambertian scattering profiles that are largely independent of the angle and polarization of incident waves. The combination of tailored positional disorder with a carefully balanced electric and magnetic response of the nanoparticles is shown to be an integral requirement for the operation as a diffuser. The proposed metasurfaces' directional scattering performance is characterized both experimentally and numerically, and their usability in wavefront-shaping applications is highlighted. Since the metasurfaces operate on the principles of Mie scattering and are embedded in a glassy environment, they may easily be incorporated in integrated photonic devices, fiber optics, or mechanically robust augmented reality displays.