The manipulation of optical modes directly in a multimode waveguide without affecting the transmission of undesired signal carriers is of significance to realize a flexible and simple structured optical network-on-chip. In this Letter, an arbitrary optical mode and wavelength carrier access scheme is proposed based on a series of multimode microring resonators and one multimode bus waveguide with constant width. As a proof-of-concept, a three-mode (de)multiplexing device is designed, fabricated, and experimentally demonstrated. A new, to the best of our knowledge, phase-matching idea is employed to keep the bus waveguide width constant. The mode coupling regions and transmission regions of the microring resonators are designed carefully to selectively couple and transmit different optical modes. The extinction ratio of the microring resonators is larger than 21.0 dB. The mode and wavelength cross-talk for directly (de)multiplexing are less than −12.8 dB and −19.0 dB, respectively. It would be a good candidate for future large-scale multidimensional optical networks.

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.