The team notes that optical communications systems that use visible lasers and LEDs suffer from interference due to sunlight and point out that transmitters and receivers must be aligned precisely.
“Accurate beam alignment for point-to-point (or line-of-sight) optical communication is challenging,” said PhD student Xiaobin Sun. “Slight movements of just a few millimetres might break the communication link. This motivated us to look for a non line-of-sight communication system.”
Because UV-B from the Sun is mostly absorbed by ozone in the upper atmosphere, it doesn’t interfere with communications. UV-B also gets scattered in different directions by aerosols and common molecules, meaning the signal spreads out from the source to cover a wide area and accurate alignment of the beam is not required.
The team, led by Professors Boon Ooi and Slim Alouini and including the Chinese Academy of Sciences, is developing high-performance UV-LED sources and highly sensitive detectors that receive UV signals quickly and accurately. In their latest work, they used an LED to send pulsed UV-B signals to a sensor comprising two antireflective lenses that collect and focus the UV-B light into a photodetector. The team observed strong power transmission, even when the angle between source and detector was increased up to 12°, demonstrating that direct line-of-sight was not required. The system transmitted data at 71Mbit/s.
“Other groups have used different types of UV sources for transmitting relatively slow non line of sight signals for communications,” said Prof Ooi. “We are the first to achieve multiple tens of Mbit/s transmission using UV-B LEDs.”
The team will now work to increase the optical power and sensitivity of the system, with the goal of developing long-distance non line-of-sight UV communications with high data rates.
