High performance mode (de)multiplexer assisted with a microring resonator on the lithium niobate-on-insulator platform.

The high extinction ratio mode (de)multiplexer is a pivotal component in high capacity mode-division multiplexing data communication and nascent on-chip intermodal acousto-optic modulators. Up to now, high performance on-chip mode (de)multiplexers are still lacking for integrated AOMs on the lithium niobate-on-insulator platform. In this paper, we propose and demonstrate an innovative scheme to achieve high extinction ratio signal routing for acousto-optic modulation, by leveraging a two-mode (de)multiplexer in conjunction with a high- racetrack microring resonator. The integrated devices are fabricated with one-step electron beam lithography and dry etching processes. The demonstrated two-mode (de)multiplexer boasts the excellent intermodal crosstalk below -20 dB and the on-chip insertion loss of less than 1.92 dB within the wavelength range of 1,514-1,580 nm. With the reinforcement of the microring resonator filter, the carrier signal can be suppressed thoroughly and the measured extinction ratio attains over 30 dB. Our proof-of-principle investigations have provided a feasible and compact solution to implement practical intermodal AOMs in LNOI for photonic and quantum information process, microwave photonics, and LiDAR.