Underwater fiber–wireless communication with a passive front end

We propose and experimentally demonstrate a novel concept on underwater fiber–wireless (Fi–Wi) communication system with a fully passive wireless front end. A low-cost step-index (SI) plastic optical fiber (POF) together with a passive collimating lens at the front end composes the underwater Fi–Wi architecture. We have achieved a 1.71-Gb/s transmission at a mean BER of 4.97 × 10−3 (1.30 × 10−3 when using power loading) over a 50-m SI-POF and 2-m underwater wireless channel using orthogonal frequency division multiplexing (OFDM). Although the wireless part is very short, it actually plays a crucial role in practical underwater implementation, especially in deep sea. Compared with the wired solution (e.g. using a 52-m POF cable without the UWOC part), the proposed underwater Fi–Wi scheme can save optical wet-mate connectors that are sophisticated, very expensive and difficult to install in deep ocean. By combining high-capacity robust POF with the mobility and ubiquity of underwater wireless optical communication (UWOC), the proposed underwater Fi–Wi technology will find wide application in ocean exploration.