Optical Wi-Fi enables ultrafast underwater communication

22 Sep 2020

EPFL spin-off Hydromea develops mini-optical modem that works at 6,000m under the sea.

Startup Hydromea, a spin-off company from École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, 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 high speeds from sources more than 50 meters away.

This is useful for researchers needing to use a connected device underwater, for example for data gathering – radio waves do not work well in these conditions because they are easily absorbed by water, meaning they cannot effectively communicate much further than a meter or so.

Acoustic communication is often used, but it is very slow and unreliable, and fixed wired connections are impractical in many situations. These are 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 (the study of inland waters) is another field affected by this problem.

However, engineers at Hydromea have come up with a solution: using light to transmit data below the ocean or lake surface. They have developed an underwater modem called LUMA that communicates through a rapidly flashing blue light.

The modem rapidly converts data into light pulses that it sends out, or inversely, converts light pulses that it receives into data. “Our optical modem gives you a fast, wireless underwater connection,” commented Alexander Bahr, Hydromea’s COO.

“We selected blue light because, even though water is generally opaque to electromagnetic waves, there is a small transparency band for blue and green light. That allows our system to send and receive data over long distances,” said Felix Schill, the company’s CTO. While water readily absorbs most wavelengths, and especially infrared ones, only blue and green light can travel through it. Red and yellow light such as from he sun are absorbed in just a few meters.

Reliability challenges

The most difficult aspect of developing LUMA was to enssure that 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 up to 100 meters was difficult,” said Schill. “It took us a long time to develop a receiver sensitive enough to capture faint light pulses even from far away.”

LUMA is designed to work at depths of up to 6,000 meters. It is a fully-sealed, encased in clear plastic so it will not 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 (AWI), in Bremerhaven, Germany.

This is the first research institute that Bahr and Schill began working with. “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 Bahr.

Bahr and Schill started researching underwater Wi-Fi systems when they were both students in Australia back in 2004. They improved their design over the years, and finalized it during their post-doc work at EPFL. Today they are still collaborating with AWI. For example, they are helping develop robotics and communications systems for LéXPLORE, a research platform located just off the shores of Lake Geneva, near Pully Vidy.

There, limnologists are using LUMA to 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.

Video explainer

The following Hydromea / EPFL video explains the design and operation of the LUMA underwater communications system: