Abstract: The present invention provides a specific gradient-optical-index porous (GRIP) layer coating on inorganic optical substrate surfaces, and the fabrication method used to create the GRIP layer coating. The method consists of two major processing steps: (1) the co-deposition of an optical index-matching material and a mass density-modulating material, followed by (2) the sacrificial etch of the mass-density-modulating material to reveal a GRIP surface. The method is designed for use with crystalline, polycrystalline, and dry or wet etch-resistant substrate materials, where anti-reflective (AR) solutions using AR surface structures (ARSSs) do not exist. These coatings are designed to minimize Fresnel reflectivity of the original substrate surfaces, using a single porous layer matched to the optical index of the original substrate material.