Inverse-designed broadband meta-coupler with high efficiency on thin-film lithium niobate

Efficiently coupling free-space light with a large bandwidth to arbitrary positions in on-chip systems is a significant challenge. In this work, we address this issue by utilizing an inverse-designed metasurface as a meta-coupler, replacing conventional grating couplers. Our meta-coupler achieved a maximum coupling efficiency of 90% (-0.46 dB). The 1-dB bandwidth spans 138 nm (1450-1588 nm), while the 3-dB bandwidth extends over 300 nm (1425- 1725 nm), far exceeding the bandwidth of traditional grating couplers used on thin-film lithium niobate. This meta-coupler demonstrates strong potential for on-chip systems requiring multi-wavelength interactions, such as integrated lasers and amplifiers. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved. https://doi.org/10.1364/JOSAB.545358