4×4 MIMO equalization to mitigate crosstalk degradation in a four-channel free-space orbital-angular-momentum-multiplexed system using heterodyne detection

We demonstrate crosstalk degradation mitigation using 4×4 MIMO equalization on an orbital-angular-momentum-multiplexed free-space data link with heterodyne detection. 20-Gbit/s QPSK signal with up to -4.8 dB crosstalk is recovered and the BER is reduced by two orders of magnitude.