Inverse-designed 1 × 2 power splitter on X-cut thin-film lithium niobate platform by DUV photonic integration

Scalar-based isotropic inverse design algorithms have been widely adopted. However, anisotropic materials pose challenges for scalar-based inverse design methods due to their direction-dependent refractive index distributions, which particularly limit the application of X-cut lithium niobate materials in inverse-designed photonic devices. Meanwhile, the predominant use of electron beam lithography (EBL) in fabricating inverse-designed devices creates bottlenecks for large-scale manufacturing, ultimately hindering their transition to practical applications. In this work, we present for the first time a 1 × 2 power splitter designed by the generalized inverse design method and fabricated via deep ultraviolet (DUV) lithography on an X-cut thin-film lithium niobate platform. The orientation-dependent properties of anisotropic material are incorporated into the adjoint method, and gradient-based optimization is utilized to generate non-intuitive structures that satisfy both functional performance and fabrication constraints. Experiments demonstrate operation over the 1520 nm-1550 nm range, with the average insertion loss (IL) of 0.7 dB and a power imbalance of less than 0.25 dB. This approach enables compact, robust device designs compatible with scalable manufacturing, offering a promising path for next-generation photonic integration.