Up-scalable method to amplify the diffraction efficiency of simple gratings.

An innovative class of coupling gratings for efficiently redirecting light beams is described. They are based on symmetric binary gratings equipped with an asymmetric high refractive index coating. This kind of structure exhibits a grating blaze effect and produces high diffraction efficiencies. Coupling gratings based on the described principle have been fabricated by UV casting and subsequent oblique ZnS evaporation. The gratings were characterized by measuring their diffraction efficiencies. For unpolarized light, efficiencies of around 70% have been measured at 510 nm wavelength. Simulations revealed that diffraction efficiencies of up to 90% can be obtained for polarized light.