“…In Refs 9,10,11,12,13,14,15, the periodically non-homogeneous dielectric material is either an isotropic rugate filter11 or a sculptured thin film (STF) that is periodically non-homogeneous along its thickness direction91012131415. STFs are a class of nano-engineered, unidirectionally non-homogeneous, and anisotropic thin films that can be fabricated using a variety of physical vapor deposition (PVD) techniques1617.…”