For weakly coupled mode-division multiplexed (MDM) transmission systems, we design and implement optical coherent receiver prototypes with real-time multiple-input multipleoutput (MIMO) digital signal processing to equalize two degenerate linearly polarized modes with dual polarization. Using field programmable gate array circuits, we implement real-value 8 × 2 MIMO adaptive equalization with externally separated phase compensators based on the least mean square algorithm, which enables not only training equalization but also fast carrierphase tracking. With the optical coherent MIMO receiver prototype, we demonstrate real-time weakly coupled 10 ×MDM wavelength-division multiplexed dual-polarization quadrature phase shift keying transmission over 48-km few-mode fibers. This report shows a record number of multiplexed spatial modes, namely, 10 modes with dual polarization, in real-time MDM transmission experiments.
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