Multimode Waveguide Bends in Lithium Niobate on Insulator

Abstract Lithium niobate on insulator (LNOI) is a promising platform for realizing high‐performance photonic integrated circuits (PICs) for communication applications due to LN's excellent electro‐optic properties. Multimode photonic devices are attractive as they can improve the communication capacity of PICs by multiplexing orthogonal modes. For connecting multimode photonic components on the same chip, multimode waveguide bends are indispensable. In this contribution, multimode waveguide bends are proposed, simulated, and experimentally demonstrated with double air grooves to ensure low crosstalk for three different transverse electric (TE) modes by improving the mode overlap at the interface between the straight and bent waveguide when the waveguide is bent. This enables demonstration of S‐shaped waveguide bends (two 90 o bent waveguides) with insertion losses below 1.42, 1.12, and 2.5 dB in the wavelength range of 1525–1575 nm for the transmitted TE 0 , TE 1 , and TE 2 modes, respectively. The mode crosstalk is lower than −12.2 dB for all three modes. The demonstrated device provides a compact solution for multimode waveguide bends in the LNOI platform, paving the way for high‐speed, high‐data‐capacity PICs for on‐chip communication systems.