Low-loss, low-crosstalk polarization-independent lithium niobate crossing waveguide based on the multimode interference coupling principle

Lithium niobate (LN) integrated crossing waveguides are essential components in photonic integrated circuits.However, the refractive index tensor of lithium niobate and the asymmetry of waveguides lead to polarization-dependent performance of LN crossing waveguides.In this Letter, a polarization-independent lithium niobate crossing waveguide on the lithium-niobate-on-insulator platform is proposed and demonstrated using the multimode interference coupling principle.Experimental results show that the proposed device exhibits low insertion losses (<-0.96dB), with crosstalk below -37 dB over the wavelength range of 1480-1640 nm.The proposed device significantly enhances the on-chip density of lithiumniobate-based photonic interconnection networks.