Broadband Adiabatic Optical Power Coupling with Multimode Operation for Mode‐Division Multiplexing Systems

Abstract Mode‐division multiplexing (MDM) technology, which utilizes spatial modes to expand optical communication capacity, has attracted increasing attention. As a fundamental building block for MDM communication systems, multimode optical power coupling is playing an important role in light transmission and optical interconnection. However, it is still very challenging to achieve optical power coupling with multimode operation over a large bandwidth. Here, we propose and experimentally demonstrate an adiabatic directional coupler (DC) and 3‐dB power splitter based on the stimulated Raman adiabatic passage scheme, which can realize broadband and mode‐insensitive power coupling and splitting for the guided E 11 , E 21 , and E 12 modes in an MDM system. Specifically, the adiabatic DC achieves the simulated coupling efficiencies >91.6% across 1450–1750 nm and measured coupling efficiencies >92.0% over 1500–1630 nm for the three modes. Furthermore, an adiabatic multimode 3‐dB power splitter for the three modes maintains near‐ideal 50%:50% power splitting ratios in simulation (<0.006 dB imbalance) and experiment (<0.11 dB imbalance) across the same operating bandwidth. This work successfully overcomes a critical challenge of achieving broadband multimode coupling in MDM systems, which demonstrates the great potential for enlarging the capacity and flexibility of MDM systems.