A double-sided grating coupler for thin light guides

A simple and efficient solution for coupling a collimated light beam into a thin light guide is presented. The approach is based on two gratings, with their grating lines perpendicular to each other, fabricated into the opposite surfaces of the light guide. The presented numerical simulation shows that an optimized double-sided solution for unpolarized light enables around 2-7 times higher incoupling efficiencies than what is possible with conventional solution based on only one grating. Experimental verification is made by using UV-replicated binary gratings on both sides of a PMMA foil.