Mode‐Division‐Multiplexing Transmitter With Anisotropy Lithium‐Niobate‐on‐Insulator Photonic Waveguides

Abstract In recent years, there is a growing interest in lithium‐niobate‐on‐insulator (LNOI) photonics due to its superior material properties, particularly its large electro‐optical (EO) coefficient. As a promising method to improve the communication capacity, mode‐division multiplexing (MDM) has received intensive attention. However, achieving effective mode manipulation is challenging due to the hybridness nature of LNOI photonic waveguides. In this work, an innovative multi‐channel mode‐division‐multiplexing transmitter is proposed that integrates eight EO modulators with an eight‐channel mode multiplexer for the first time. To leverage the EO effect and enable on‐chip mode manipulation, the EO modulators are strategically designed along the y ‐propagation direction to access the largest EO coefficient. Conversely, the mode multiplexer is designed along the z ‐propagation direction to mitigate mode hybridness. Experimental results demonstrate that the present MDM transmitter exhibits low loss (<2.5 dB) and low crosstalk (−12–−17 dB) across the C‐band. The modulator features a voltage‐length product of 2.7 V·cm and an RF modulation damping of 2.0 dB even at 67 GHz. With the implementation of the proposed MDM transmitter, successful high‐capacity data transmissions of 8 × 60 Gbps On‐Off‐Keying signals and 8 × 50 Gbps four‐level pulse amplitude signals have been achieved with a single wavelength‐carrier.