Mode-folded thin-film lithium niobate phase shifter for channel scalable optical interconnect with high switching efficiency

Paralleled optical interconnection has been widely used in optical transceivers. Reconfigurable photonic integration with scalable channel numbers is thus highly useful in timely adjusting the link capacity to the changing traffic patterns in data centers or high-performance computing (HPC) systems. In this paper, a 1×8 Mach–Zehnder switch (MZS) over thin-film lithium niobate is proposed and experimentally demonstrated for 1-to-8 channel scalable optical interconnects, with high switching efficiency through utilizing the mode-folded phase shifter. The three-mode phase shifter recirculates the light three times, undergoing phase changing with different waveguide modes. Simultaneously, the multimode waveguiding within the phase shifter results in a pronounced enhancement of the optical field confinement, further improving the Pockels effect for all modes. A 3.5-time improvement of the switching efficiency is experimentally demonstrated, exhibiting a low Vπ·L of 0.6 V·cm. The proposed MZS also features low channel crosstalk (below -20 dB over 1530-1565 nm) and nanosecond-order switching time, paving the way towards channel scalable and versatile MSA-compatible optical interconnect.