Coupled-Core Transmission at 100-Gbaud with Low-Complexity, Fast-Tracking 4D × D MIMO Equalizer

Space division multiplexing (SDM) has emerged as a pivotal technology for scaling the capacity of future high-capacity optical transmission systems. Large-scale multiple-input/multiple-output (MIMO) digital signal processing-based SDM systems that utilize media with inherent strong crosstalk between spatial channels, such as coupled-core multicore fibers, are particularly promising for achieving unprecedented transmission capacities. To alleviate the inherent complexity of these massively parallel systems, an SDM-MIMO signal processing scheme needs to be developed that can efficiently handle high-symbol-rate transmissions. In this context, we present a partially frozen (PF) 4D×D multiple-input/multiple-output adaptive equalizer (MIMO AEQ), tailored specifically for robust high-symbol-rate SDM-MIMO signal reception. This approach is designed to combat electrical IQ impairments—a predominant obstacle in high-symbol-rate transmission—while simultaneously enhancing tracking ability to channel dynamics and reducing computational complexity. We detail the operational principles of the PF 4D×D MIMO AEQ and validate its performance through simulations and experiments. Our results underscore its validity, demonstrating a net transmission of 2.6 (0.65×4) Tb/s/λ over a dynamically fluctuating four-coupled-core cabled transmission line using 100-Gbaud 16QAM signals.