LiFi goes underwater
A spin off from EPFL in Switzerland has developed a light-based LiFi data modem that can operate underwater at great depths
Hydromea has developed a miniature optical modem that can operate down to 6,000 meters below the ocean’s surface. It is sensitive enough to collect data at very high speeds from sources more than 50m with data arates of 500kbit/s.
Radio doesn’t work well underwater, so sonar tends to be used instead, but both are limited in the data rate they can carry. This creates significant obstacles to effective communications when it comes to underwater construction, inspection, monitoring and repair activities – such as in the offshore energy sector. Limnology research is another field affected by this problem.
The LUMA modem communicates through a rapidly blinking blue light with the light pulses carrying the data in a way similar to the light-based version of WiFi.
“We chose blue light because even though water is generally opaque for electromagnetic waves, there is a small transparency band for blue and green light. That’s what lets our system send and receive data over long distances,” said Felix Schill, the company’s CTO. While water readily absorbs most waves, and especially infrared ones, just blue and green light can travel through it. The red and yellow light waves of the sun are absorbed in just a few meters.
The hardest part about developing LUMA was making sure it could send data over long enough distances and work reliably under all sorts of conditions. “Because light generally diffuses so rapidly underwater, finding a way to send communications over distances of 50 or 100 meters was difficult,” said Schill. “It took us a long time to develop a receiver sensitive enough to capture tiny light pulses even from far away.” There are four transmission power levels from two to five watts and a wide supply voltage range.
LUMA is designed to work at depths of up to 6,000 meters. It’s a fully contained unit in a plastic casing, which is completely encased in clear plastic so it doesn’t collapse under extreme water pressures. The system has already been tested in the Pacific Ocean, at 4,280 meters below sea level, by scientists at the Alfred Wegener Institute for Polar and Marine Research, in Germany.
“We were later contacted by companies operating offshore that were interested in our technology for laying underwater pipelines or building foundations for offshore wind farms,” said Alexander Bahr, Hydromea’s COO.
Bahr and Schill are helping develop robotics and communications systems for LéXPLORE, a research platform located just off the shores of Lake Geneva, neat Pully Vidy.
There, limnologists are using LUMA to regularly check on the data collected underwater and make sure the measurement instruments are working properly, since the sensors need to remain underwater for months at a time. One modem is installed on the data logger which collects scientific data from the submerged sensors and the other modem is installed on a subsea robot that dives down to where the sensors are located and collects the sensors’ data instantly. “The LéXPLORE scientists give us feedback on their specific needs, and this helps us further improve our modem’s performance,” said Bahr.
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