One of the limiting factors of underwater remotely-operated vehicles (ROVs) is the fact that, in order for their operators to see what the ROVs' cameras are seeing, the craft have to be physically connected to a surface support ship via a long tether. Scientists are working on changing that, via a two-way system that uses lasers to wirelessly transmit ultra-HD video through the water.
The underwater wireless optical communication (UWOC) system was created by PhD student Abdullah Al-Halafi and his supervisor Basem Shihada, at Saudi Arabia's King Abdullah University of Science and Technology (KAUST). So far it's been tested in a lab setting, successfully sending and receiving signals through up to 4.5 meters (14.7 ft) of both clear open-ocean water, and siltier harbor water.
It incorporates an underwater platform that converts ultra high-definition digital video into a series of extremely rapid pulses, which are emitted by a 520-nanometer green laser diode. These form a downlink channel, travelling through the water and being picked up by a photodiode-equipped receiver, which converts them back into real-time video.
That receiver in turn uses a 450-nm blue laser to form an uplink channel, which transmits data back to the underwater platform. Included in that data is feedback on the signal quality of the received video. Based on that feedback, the underwater platform adapts the power and modulation of its video signal, in order to compensate for the clarity of the water. This means that if the water is fairly clear, more video packets can be transmitted at faster rates, but if it's silty, the video quality is maintained by slowing down the rate of video transmission.
"The end user will not experience any difference in video quality, as the system delivers video packets with the same definition, but at optimized power and transmission rates," says Al-Halafi.
Data transmitted on the uplink channel could also include commands, which operators would use to remotely control the ROV. And while this isn't the first UWOC system we've seen, it reportedly has achieved the highest resolution and fastest transmission rate for underwater video.
A paper on the research was recently published in the IEEE Photonics Journal.
Source: KAUST
They should use magnetics. The *reason* radio-waves (which don't go through water at all well) are called Electro-MAGENTIC-radiation, is because the other half of that energy is not radio (aka light), but magnetic. A decent loop antenna picks that up.