High-efficiency chirped grating couplers on lithium niobate on insulator

High-efficiency chirped grating couplers (GCs) with coupling efficiencies (CE) approaching 90%/coupler were designed by using a particle swarm optimization algorithm. These GCs were fabricated on -cut lithium niobate on insulator (LNOI) with an Au layer on the lithium niobate substrate. The maximum CEs for transverse electric and transverse magnetic polarization input were measured up to /coupler and /coupler, respectively, which are the state-of-the-art values for LNOI GCs as far as we know. These GCs contribute to the realization of high-efficiency LNOI on-chip integrated optics.