Demonstration of 8-mode 32-Gbit/s millimeter-wave free-space communication link using 4 orbital-angular-momentum modes on 2 polarizations

This paper reports an experimental demonstration of modal multiplexing using orbital angular momenta (OAM) in the millimeter-wave regime (28 GHz). Using 1 GBaud/s signals with 16-QAM modulation, a data rate of 32 Gbit/s is obtained by employing 4 different OAM modes (l= -3,-1,+1 and +3) on two orthogonal linear polarization states. Without any digital post-processing, the receiver can separate the different data streams since crosstalk among the OAM channels is low: measured to be better than -23dB with a 28 GHz narrowband carrier on a single polarization, and better than -16dB on both polarization states. The bit-error rate (BER) of 8 channels is measured, and found the raw BER is below 3.8×10^-3, thus allowing efficient use of forward error correction (FEC) codes.