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) 4DxD 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 4DxD MIMO AEQ and validate its performance through simulations and experiments. Our results underscore its validity, demonstrating a net transmission of 2.6 (0.65x4) Tb/s/lambda over a dynamically fluctuating four-coupled-core cabled transmission line using 100-Gbaud 16QAM signals.