Space-division multiplexing (SDM) has been expected to support the continuous growth of transmission capacity. However, it suffers from high computation complexity that limits its physical implementations. In this paper, we propose and experimentally demonstrate a low-complexity MIMO equalization method to leverage the sparsity of weights and reduce the complexity by L1&L2-regularization in long-haul space-division multiplexing (SDM) systems. The L1-regularization finds the sparse solution of equalizer filters and substitutes it for optimal solution, reducing the complexity with performance degradation. On the other hand, the L2-regularization tends to produce a smoother estimation than L1 regularization and is therefore more robust to large variance. We conduct a 39.87-GBaud QPSK coherent optical transmission experiment based on a 4-core coupled-core fiber with the transmission distance from 1206-km to 7236-km. Comparisons on the equalization performance and computational complexity show that the sparse equalizer using L1&L2-regularization achieves a 30% reduction in complexity at the similar system performance, compared with the traditional time-domain MIMO.

The record 203 Tb/s and 102 Tb/s SDM transmission enabled by $\mathrm{C}+\mathrm{L}$ band FIFO-less MC-EDFA over 3105 km and 7245 km weakly-coupled 4-core MCF with $125-\mu \mathrm{m}$ cladding diameter was first experimentally demonstrated using PCS-16QAM and PDM-QPSK, respectively. Effective cost was achieved by G.652-compatible MCF and fully-integrated-components multicore EDFA.

A randomly coupled 4-core MCF 6030-km transmission with FIFO-less weakly-coupled MCF EDFA is first experimentally demonstrated. 115.4Gb/s net-rate PDM-QPSK signals with error-free transmission are realized in 122 of 137 channels over the entire super-C band.

We propose a low-complexity frequency-domain MIMO equalization scheme combining unconstrained frequency-domain equalization with out-of-band exclusion. Long-haul strongly-coupled multi-core fiber transmission experiment shows a 73% complexity reduction with negligible performance degradation using the proposed scheme.

A unified amplification structure based on FIFO-less weakly coupled MCF EDFA over randomly and weakly coupled 4-core MCF long-haul transmission is first experimentally demonstrated. The advantage of integrated EDFA is discussed.

Frequency-domain MIMO equalizer with fractional oversampling is proposed for Randomly-Coupled multi-core fiber transmission systems, and the performance is experimentally evaluated with 137-ch 39.87-GBaud PDM PCS16-QAM WDM signal.

We propose a modified frequency-domain MIMO with cyclic prefix to combat the temporal spread for different modes and largely reduce the complexity of the equalization. After 80-km FMF transmission, the proposed MIMO has almost the same performance as conventional FDE with a proper CP length while the complexity is reduced by 7.4 times.

A 109.6 Tb/s real-time SDM transmission over 2024 km weakly coupled 4-core multicore fiber with standard cladding diameter was experimentally demonstrated. 137-channel PS-PDM-16QAM signals were transmitted in super C-band with commercial single-mode 200G OTN transmission platform, and negligible performance degradation, introduced by the crosstalk of multicore fibers and Fan-In/Fan-Out devices, was confirmed.