Highly Efficient and Ultrabroadband Hybrid Silicon-Lithium Niobate Grating Coupler

We propose and design a highly efficient and ultrabroadband grating coupler based on the hybrid Silicon and Lithium Niobate platform. By using a triple layer structure and a bottom metal reflector, simulation results demonstrate that the minimal insertion loss is about −0.15dB and the 1-dB optical bandwidth is up to 135 nm. Such a broadband and highly-efficient grating coupler is suitable for various thin film Lithium Niobate devices.