High coupling efficiency grating couplers on lithium niobate on insulator

We demonstrate monolithically defined grating couplers in Z-cut lithium niobate on insulator for efficient vertical coupling between an optical fiber and a single mode waveguide. The grating couplers exhibit similar to 44.6%/coupler and similar to 19.4%/coupler coupling efficiency for TE and TM polarized light respectively. Taperless grating couplers are investigated to realize a more compact design. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement