A SiPM-Based Optical Modem for Underwater Wireless Communication: Experiments in Turbid Waters

The high bandwidth capability of optical wireless communication has sparked interest in underwater applications. Communication links beyond 100 meters can be established in clear waters, supporting the adoption of optics in short-range operations. While the level of water clarity highly affects the maximum transmission range, the type of photodetector used to receive the transmitted light also plays a significant role. In this paper, we investigate the feasibility of using a sensitive silicon photomultiplier (SiPM). The latter is integrated as part of a bidirectional optical modem using 450 nm blue LEDs as the transmitting light source. Experiments conducted near a harbor in Oslofjord, Norway, are compared to a channel model for both daytime and nighttime conditions. During the day under a clear sky, the sea trials resulted in a bit error rate (BER) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.21 \ \mathrm{x} 10^{-3}$</tex> at 15 meters for a 1 Mbps NRZ-OOK modulated signal. In the evening, with reduced ambient noise, the optical modem achieved a transmission distance of up to 18 meters with a BER of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.85 \ \mathrm{x}\ 10^{-3}$</tex> in the turbid harbor.