One-to-many data information transfer, also known as multicasting, is desired in underwater wireless communications when distributing signal between multiple users. In this paper, by exploiting the space domain (spatial phase structure) of lightwaves, we propose and demonstrate an orbital angular momentum (OAM)-based underwater wireless optical multicasting link. 2-meter underwater transmission of 4-fold green light (520 nm) OAM modes multicasting (OAM-6, OAM-3, OAM+3, OAM+6), each channel carrying 1.5-Gbaud 8-ary quadrature amplitude modulation (8-QAM) with orthogonal frequency-division multiplexing (OFDM) signal, is demonstrated in the experiment. The OAM spectrum after underwater propagation suffers some degradation with the crosstalk between multicasting OAM channels and other unwanted channels measured to be less than −6 dB. Bit-error rate (BER) performance is characterized with ~2 dB penalty. Higher-order modulation signals (16-QAM-OFDM, 32-QAM-OFDM) are also considered in free-space OAM multicasting link for comparison.
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Zhao et al. (2017) studied this question.
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