Remotely operated underwater vehicles (ROVs) are increasingly being used for underwater construction, research or drilling activities. Among other things, these handy little vehicles are equipped with camera so that a good view of the work can be kept. A limiting factor here is the connection between camera and monitoring station on board a vessel where operators do their work. This usually requires the ROV to be physically connected to the ship via a long cable. Scientists are now working on a two-way system with lasers that can simultaneously transmit ultra HD video image and control commands through the water.
This underwater wireless optical communication (UWOC) system is being worked on by scientists at a university in Saudi Arabia. The system has now been successfully tested in a laboratory environment. In this, signals over a distance of 4.5 metres were sent and received by the ROV. The test was conducted in both clear ocean water and saltier water from the port.
The ultra HD video signal is converted on board the ROV into extremely fast pulse signals transmitted by a green laser diode at 520 nanometres. This signal to the vessel travels through the water and is received by a photodiode receiver that converts the laser signal back into video images.
The receiver uses a 450 nm blue laser for the data connection to the ROV. The data sent back includes not only the operator's control commands but also information about the signal quality of the received image. Based on this, the ROV adjusts the power and modulation of the video signal to compensate for the clarity of the water. If the water is quite clear, more video packets can be transmitted at higher speed. In saltier water, video quality is maintained by reducing the transmission rate.
