Integrated lithium niobate optical mode (de)interleaver based on an asymmetric Y-junction.

Lithium niobate on insulator (LNOI) platforms promise unique advantages in realizing high-speed, large-capacity, and large-scale photonic integrated circuits (PICs) by leveraging lithium niobate's attractive material properties, which include electro-optic and nonlinear optic properties, low material loss, and a wide transparency window. Optical mode interleavers can increase the functionality of future PICs in LNOI by enabling optical mode division multiplexing (MDM) systems, allowing variable mode assignment while maintaining high channel utilization and capacity. In this Letter, we experimentally demonstrate an optical mode interleaver based on an asymmetric Y-junction on the LNOI platform, which exhibits an insertion loss of below 0.46 dB and modal cross talk of below -13.0 dB over a wavelength range of 1500-1600 nm. The demonstrated mode interleaver will be an attractive circuit component in future high-speed and large-capacity PICs due to its simple structure, scalability, and capacity for efficient and flexible mode manipulation on the LNOI platform.

Integrated lithium niobate polarization beam splitter based on a photonic-crystal-assisted multimode interference coupler.

Lithium niobate on insulator (LNOI) is a promising platform for high-speed photonic integrated circuits (PICs) that are used for communication systems due to the excellent electro-optic properties of lithium niobate (LN). In such circuits, the high-speed electro-optical modulators and switches need to be integrated with passive circuit components that are used for routing the optical signals. Polarization beam splitters (PBSs) are one of the fundamental passive circuit components for high-speed PICs that can be used to (de)multiplex two orthogonal polarization optical modes, enabling on-chip polarization division multiplexing (PDM) systems, which are suitable for enhancing the data capacity of PICs. In this Letter, we design and experimentally demonstrate a high-performance PBS constructed by a photonic crystal (PC)-assisted multimode interference (MMI) coupler. The measured polarization extinction ratio (ER) of the fabricated device is 15 dB in the wavelength range from 1525 to 1565 nm, which makes them suitable for the high-speed and large data capacity PICs required for future communication systems.