Experimental demonstration of underwater wireless optical OFDM communication system with a single SPAD receiver

Generally, only binary modulation formats, such as on–off keying (OOK) and pulse position modulation (PPM), can be detected by a single photon avalanche diode (SPAD). In this paper, we propose to use a single SPAD receiver to achieve underwater wireless optical communication (UWOC) with high-order modulation formats. The feasibility is theoretically analyzed, and firstly demonstrated in a proof-of-concept orthogonal frequency division multiplexing (OFDM) experiment. The proposed OFDM system using quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) can work with less than 68 and 390 photons per symbol, and with receiver sensitivities below the forward error correction (FEC) limit as high as −84.5 dBm and −77.8 dBm, respectively. These extraordinarily sensitive results indicate that the proposed scheme is a promising solution to long-distance UWOC systems or internet of underwater things (IoUT).