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Performance analysis of spectrally efficient free-space data link using spatially multiplexed orbital angular momentum beams

In this paper, we present the measurement results of a spectrally efficient 2.56Tb/s free-space data link using orbital angular momentum (OAM) beams. This link includes 32 independent 20 Gbaud/s 16-quadrature-amplitude-modulation data streams, each encoded on a different OAM beam, which are mode-, polarization- and space-division multiplexed as one collocated beam. We measured the bit-error rate (BER) curves of all 32 channels, all of which can achieve a BER of <2×10-3. The performance degradation due to the spatial multiplexing using concentric ring scheme is analyzed. Additionally, the effect of the pre-filtering is investigated, and negligible penalty is observed.