Low Complexity Equalization Using Mode-Subset Selection in MIMO Multimode Fiber Links

Optical fiber links have enabled the transmission of very high data rates over both short-range and long-range links. However, the recent growth in the bandwidth demand has created the need to enhance their data rate capacities. While modern modulation techniques and multiple-input multiple-output (MIMO) based mode-division multiplexing (MDM) techniques with multimode fibers (MMFs) have been demonstrated to be promising approaches to achieve higher data rates, the computational complexity required to perform data decoding at these high data rates makes these systems prohibitive. In this paper, we model the channel characteristics and mode-dependent losses of few-mode and many-mode MMFs and study the data rates obtained if only a few modes are chosen for decoding at the subset. Such an approach promises to reduce the decoding complexity while not sacrificing data rate significantly. Simulations reveal that a subset selection approach leads to large savings in computation while not compromising data rate significantly. In particular, the energy-per-bit requirement can be reduced by over 50% in few-mode fibers and upto 70% in large-core multimode fiber links, when compared to conventional MDM decoding.