Five-Fold Partitioned 30 × 30 MIMO Equalization Using Mode-Group Specific Interface Quantization in 15-Mode Fiber SDM Transmission

The increasing capacity demand of optical communication systems has driven research on space-division multiplexing (SDM) using few-mode fibers (FMFs). While FMFs provide high spatial efficiency, their practical deployment is limited by the rapidly growing complexity of multiple-input multiple-output (MIMO) digital signal processing (DSP). Partitioned-MIMO architectures reduce DSP complexity by exploiting the existence of mode groups (MGs) in FMFs, where intra-group coupling is strong and inter-group coupling is weak. In this work, we experimentally investigate a partitioned MIMO architecture with mode-group specific interface quantization for a 15-mode FMF transmission system, which would otherwise require a full 30 × 30 MIMO equalizer. The equalizer is decomposed into five MG-specific sub-equalizers with low-resolution, MG-dependent inter-partition signal exchange to compensate residual inter-group coupling. Using 24.5-GBd dual polarization QPSK transmission over a 58.9-km graded-index FMF, we evaluate the impact of interface quantization on the achievable signal-to-noise ratio (SNR). The results show that weak inter-group coupling can be omitted entirely, while stronger neighboring MG interactions require only three to four bits to limit SNR penalties to below 1.7 dB relative to a uniform five-bit reference. This approach significantly reduces inter-partition interface throughput while preserving equalization performance, demonstrating the scalability of partitioned-MIMO architectures for high-capacity SDM systems.