Broadband, high-efficient and compact inverse-designed crossing on thin-film lithium niobate platform

Lithium niobate on insulator (LNOI), with its excellent electro-optic properties, high transparency, and stability, has been widely used in high-speed photonic integrated circuits (PICs). Waveguide crossings are one of the most fundamental and critical interconnect structures in PICs. They enable efficient, low-loss, and low-crosstalk transmission of optical signals at waveguide intersections, thereby facilitating complex optical routing in two-dimensional planes. We demonstrate an improved broadband, low-loss, compact LNOI waveguide crossing covering portions of the S-band and fully spanning the C, L, and U bands. Using the adjoint algorithm, the design achieves <0.12 dB insertion loss and < −40 dB crosstalk over 180 nm bandwidth, with best-case values of 0.05 dB and −50 dB. Its 16 × 16 μm2 footprint is smaller than comparable designs. This work demonstrates the viability of high-performance, compact inverse-designed devices on the LNOI platform, advancing possibilities for high-density photonic applications in data centers and quantum photonics.