Using Standard 2×2 MIMO to Increase Capacity of Spatial Multiplexing with OAM Modes

Modal multiplexing can greatly increase fiber capacity, but often at the cost of high digital processing with multiple-input multiple-output (MIMO) algorithms. The use of orbital angular momentum (OAM) for multiplexing can support MIMO-free reception, but it always operates in an interferencelimited regime. Many previous MIMO-free demonstrations for OAM used a type of optical MIMO that is impractical for deployed systems. We compare the performance of MIMO-free and standard electronic 2 × 2 MIMO in a demonstration with no recourse to optical MIMO. We show that the receiver complexity of these two reception strategies is very similar in hardware and signal processing. We explore commercial coherent receivers with 2 × 2 MIMO, hence this solution for OAM demultiplexing can be deployed effectively with current technology. The 2 × 2 MIMO reception enhances the total bit rate and is more compatible with wavelength division multiplexing (WDM) as it equalizes performance across the C-band. At 1.3 km transmission, the net bit rate spans 426–450 Gb/s across wavelengths with 2 × 2 MIMO, while variability is high for MIMO-free reception, spanning 200–418 Gb/s.