Demonstration of Distance-Dependent Data Channel Recovery in a 40-Gbit/s QPSK 2-Channel Mode-Multiplexed FSO Link by Varying the Longitudinal Wavenumbers of Structured Light

We experimentally demonstrate tunable distance-dependent data channel recovery in a 40-Gbit/s QPSK MDM FSO link by varying the longitudinal wavenumbers of structured beams. Data channel privacy is enhanced by a $\gt25 \mathrm{~dB}$ power difference between the received signals at the intended and undesired locations.