LiFi goes underwater

September 23, 2020 //By Nick Flaherty
Hydromea has developed a LiFi optical modem that can operate down to 6,000m and collect data over 50m
Hydromea has developed a LiFi optical modem that can operate down to 6,000m and collect data over 50m

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

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