Marine researchers and operators during their daily work need consistent data from the underwater environment to constantly monitor the habitat’s probes and the robots condition. For underwater applications, wireless communication are of paramount importance. Today, the needs for high-speed communication has prompted the exploration of the Underwater Optical Wireless Communications (UOWC) method. This article presents the design and validation aspects of the optical layer of a bidirectional UOWC system developed in the framework of the European Project SUNRISE, able to provide wireless connectivity compliant to 10Base-T Ethernet protocol (Manchester-coded signal with 10 Mbit/s data rate). The designed modems are made of two similar optical transceivers, each including a transmitter, a receiver unit and an optical power monitor part. The transmitter is based on an array of blue Light Emitting Diodes (LEDs), the receiver exploits a commercially available Avalanche Photodiode (APD) and the monitoring relies on a pin-photodiode. The modems, after a deep characterization in controlled environments, were proved to work with the required 10Base-T Ethernet, up to 7.5 m distance in shallow harbor waters. The complete optical system is intended to become a node of the SUNRISE infrastructure

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A new pair of optical wireless modems has been realized, which exploit Visible Light Communication (VLC) to transmit Ethernet signals through water. The modem prototypes are finally tested in sea waters at La Spezia harbor; they successfully transmitted 10 Mbit/s 10Base-T signals over a up to 10 m, notwithstanding the high turbidity and the strong sunlight.Final tests included the integration with SUNRISE testbed and the use with a moving robot, remotely operated. Commercial components were used to realize the modems; thus, we expect that the key design concepts can be used as a starting point for practical deployment of this technology.

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