Ultra-compact Y-branch splitter on thin-film lithium niobate substrate

We have proposed and demonstrated an ultra-compact Y-branch splitter on the thin-film lithium niobate (TFLN) platform with topology optimization. Fabrication constraints, such as minimum feature size and radius of curvature, are also involved within the optimization process. With optimized design and high aspect ratio etching techniques, the footprint of Y-branch splitter is only 6 μm ×4 μm while the average insertion loss is as low as 0.12 dB within 40 nm operation wavelength range. This work provides a potential solution for large-scale TFLN photonic integrated circuits in optical telecommunications and quantum photonics.