Effects of grating heights on highly efficient unibond SOI waveguide grating couplers

Abstract

The effect of the grating height upon the output efficiency of grating couplers was evaluated. Good agreement between measured values and the perturbation theory used to design the couplers allowed the design or prediction of the optimum grating height of the couplers to obtain the maximum output efficiency toward either the surface or the substrate and hence a highly efficient waveguide grating coupler. An Si rectangular grating coupler with 70% output efficiency, the highest ever reported, was also fabricated.