Experimental Demonstration of a 20-Mbit/s per Channel Free-Space Bi-directional Quantum Communication Link Using Orbital-Angular-Momentum Encoding and Multi-Port Mode Converters

We experimentally demonstrate a free-space, bi-directional quantum communication link encoded by two OAM states using multi-port mode converters. We achieve a quantum-symbol-error-rate of ≈ 0.058 for each channel at 20 Mbit/s/channel when OAM mode-spacing is 4.