Titanium dioxide-assisted metal focusing grating couplers for thin-film lithium niobate waveguides

Abstract

Thin-film lithium niobate (TFLN)-based photonic integrated circuits (PICs) demand efficient, compact, and simply realizable grating couplers for optimal performance. This work introduces titanium dioxide (TiO2)-assisted metal focusing grating couplers (TMFGCs) as a promising solution. The TMFGCs leverage a simplified fabrication process based on metal gratings. Moreover, they achieve a smaller footprint compared to previous one-dimensional metal grating couplers (GCs). Theoretical simulations predict a 1.3 dB enhancement in coupling efficiency (CE) due to the integrated TiO2 structure. Experimental results demonstrate a maximum coupling efficiency of -4.88 dB, with the potential to reach -4.07 dB through refined fabrication techniques. The TMFGCs offer a simple yet effective approach to efficient light coupling in TFLN-based PICs. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.