Wide-Angle Reflection Suppression of Dielectric Slabs Using Nonlocal Metasurface Coatings

Any discontinuity of constitutive parameters along a wave propagation path causes scattering. For a plane wave incident onto a flat dielectric slab, reflection becomes strongly dependent on the incident angle as the electrical thickness becomes large. This behavior limits the applicability of conventional single-and multilayer anti-reflective coatings. Recently, inspired by the generalized Huygens’ condition, synthesized grid impedance sheets implemented as metasurfaces with local response have been shown to remove reflection from a dielectric slab in a wide range of incident angles, applicable, however, only in the case of small optical slab thickness. In this work, we study plane wave transmission through dielectric slabs with arbitrary thickness coated on both sides with identical metasurfaces with nonlocal response, whose grid impedance is angularly dependent (spatially dispersive). Nonlocality is shown to play a key role in obtaining wide-angle reflection suppression in the case of optically thick slabs. To validate our approach, we study a metasurface implementation composed of Interconnected-Split Ring Resonators that approximates the predicted spatial dispersion law. As demonstrated numerically and experimentally, such properly devised coatings with spatially dispersive grid impedance indeed provide transmittance enhancement (and reflectance suppression) of thick dielectric slabs across a broad range of angles, paving the path to optically thin and easy-to-fabricate anti-reflective coatings efficiently operating in a wide angular range even for optically thick dielectric slabs.