Abstract
Lithium niobate on insulator (LNOI) is a highly promising platform for integrated photonics. However, existing LNOI waveguide crossings often suffer from relatively high insertion loss and strong sensitivity to fabrication-induced sidewall roughness because they typically rely on narrow waveguide designs. To address these issues, we propose a broadband and low-loss waveguide crossing for multimode waveguide systems on the Z-cut LNOI platform. The design is based on the multimode interference (MMI) self-imaging principle, and the geometric parameters of the MMI region and taper waveguides are optimized accordingly. Finite-difference time-domain (FDTD) simulations show that, for TE0-mode input at 1550 nm, the device achieves a TE0 transmittance of −0.013 dB (99.7%), a cross-port crosstalk of −49 dB, and a TE0–TE2 intermodal crosstalk of −39 dB. The proposed device also exhibits excellent wavelength insensitivity across the 1500–1600 nm band and favorable fabrication tolerance to critical dimension variations. This waveguide crossing can serve as a key building block for high-density LNOI photonic integrated circuits (PICs) for optical communication applications.