Block-Diagonal MIMO Equalization for Polarization-Multiplexed OFDM Transmission With Direct Detection

We propose a novel digital signal processing (DSP)-based multiple-input-multiple-output (MIMO) equalization algorithm set for polarization-multiplexed orthogonal frequency-division multiplexing transmission with direct detection (POLMUX-OFDM-DD), based on block-diagonal matrix processing. The new methodology significantly reduces legacy zero forcing (ZF)-based equalization complexity, and enables performance gains via efficient minimum mean square error (MMSE) and maximum likelihood (ML) detection. The new block-diagonal MMSE and ML algorithms are experimentally shown to extend transmission distance from 870 to 900 km and beyond 960 km, respectively, in 20-Gb/s standard single-mode fiber (SSMF) POLMUX OFDM quadrature-phase-shift-keying (QPSK)-DD transmission. The new algorithms are highly attractive for future cost-efficient, DSP-based optical metro/access systems.