A High Efficiency Grating Coupler Based on Hybrid Si-Lithium Niobate on Insulator Platform

In this paper, a high efficiency grating coupler based on the Si thin film on Lithium Niobate (LiNbO 3 , LN) on insulator (LNOI) platform (Si-LNOI) was developed and analyzed. Two-dimensional finite-different time-domain (2D-FDTD) simulations were performed to optimize the grating structure. Those parameters (e.g., the layer thickness of SiO 2 , LNOI, and Si) and grating configuration were numerically investigated for the coupling efficiency. A coupling efficiency exceeding 98% at λ =1550 nm was obtained for TE polarization. Furthermore, the deviation tolerances of the grating period, the filling factor, the etching depth, and the layer thickness of the Si waveguide layer were studied systematically. The results indicated a high deviation tolerance. The grating coupler presented in this study could be achieved without adding fabrication steps other than etching, thereby showing high coupling efficiency and low fabrication complexity.