SVD-Assisted Joint Pre- and Post-Equalization in Optical MIMO System

In recent years, the surge in capacity demands and cost-effectiveness have been beyond the ability of single-mode fiber (SMF) operating optical networks. In this work, the capacity crunch is dealt with by utilizing an optical multiple-input and multiple-output (MIMO) technology integrated with higher-order modulations (HOMs) as they lead to higher spectral efficiency. The low cost is achieved using intensity modulation / direct detection (IM/DD) system with a multi-mode fiber (MMF) transmission link. Contrary to an SMF channel, a highly dispersion-impaired MMF is equalized using a jointly designed pre- and post-equalization (PPE) filter, which consists of just two-taps pre-equalizer. A numerical optimization is defined to optimize the pre-and post-equalizer coefficients within the provided power and cost budgets. This work is the first investigation of a singular value decomposition (SVD) based joint-PPE scheme with a 1km long MMF link. The obtained results reveal that the signal-to-noise-ratio (SNR) gains of 5.48 dB and 10.57 dB at 10–4 bit-error rate (BER) for PAM-2 and PAM-4 compared to post-equalization only (PE-only) respectively. From the results, the SVD-assisted joint-PPE yields benefit in the presence of an MMF channel.