UV-written grating couplers on thin-film lithium niobate ridge waveguides

Grating couplers on thin-film lithium niobate ridge waveguides were designed and fabricated using UV-laser ablation. The calculated coupling efficiency with a sinusoidal grating can be as large as 53% in a 0.5 µm thin film. The maximum grating depth we fabricated was 130nm, limiting the coupling efficiency to a theoretical value of 18%. We fabricated grating couplers on adhered ridge waveguides of 20 µm thickness. Coupling light to waveguides on thin-film lithium niobate is still challenging, and here we present a fast, cheap and reliable fabrication alternative. It will benefit the on-chip testing of integrated components developed on this novel and promising material platform.