Realization of alignment-tolerant grating couplers for z-cut thin-film lithium niobate

We present the design. modeling, fabrication. and characterization of grating coupler devices for z-cut lithium niobate near 1550 nm. We first experimentally measure the sensitivity of the insertion loss of a conventional grating coupler to translational misalignment through a three-factor full factorial design of experiment. Next, we design grating couplers that are significantly less sensitive to misalignment. The fabricated devices experienced less than 7 dB of excess insertion loss for combined misalignments of up to +/- 5 mu m in plane and up to -2 mu m or + 10 mu m out of plane. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement