An optical metamaterial with simultaneously suppressed optical diffraction and surface reflection

Diffraction-free propagation of light has been demonstrated in free space for Bessel-like beams and for arbitrary beams in specially designed photonic crystals and metamaterials. The phenomenon is called self-collimation in photonic crystals and canalization in metamaterials, as the approaches to obtaining the effect are different. In both cases, however, diffraction-free propagation of light is achieved by making the dispersion surface of the material at a given frequency flat. In photonic crystals this is done by tuning the unit-cell dimensions close to the band-gap regime, and in metamaterials by tuning a hyperbolic-type metamaterial towards its transition to an ordinary elliptical metamaterial. In this work, we propose an alternative way to suppress optical diffraction in a metamaterial by adjusting the anisotropy of the finite-sized three-dimensional metamolecules and the material's spatial dispersion. The approach allows matching the wave impedance of the material to that of the surrounding medium in a wide range of incidence angles and thereby also suppressing optical reflection from the material's surface. (paper)