High-speed communication systems based on ultraviolet radiation are presently in sight.
Civil and military authorities could obtain benefits from secure optical communication systems that make use of light in order to carry messages between moving vehicles. KAUST researchers have succeeded in demonstrating rapid data transfer employing ultraviolet-B (UV-B) light, which offers a number of advantages over visible light.
Optical communications systems employing light emitting diodes (LEDs) and visible lasers suffer from interference because of the increasing levels of visible light in sunlight. Additionally, it is necessary for the receiver and transmitter to be aligned in an extremely precise manner, which is extremely difficult for vehicles on the move.
"Accurate beam alignment for point-to-point (or line-of-sight) optical communication is challenging-slight movements of just a few millimeters might break the communication link," states PhD student Xiaobin Sun who worked on the project along with professors Boon Ooi and Slim Alouini, together with other coworkers at KAUST and the Chinese Academy of Sciences in Beijing. "This problem motivates us to look for a nonline-of-sight communication system."
This is indeed where UV-B becomes useful. UV-B from the sun is generally absorbed by ozone present in the upper atmosphere, so it does not interfere with communications. Furthermore, UV-B gets scattered in varied directions by common molecules and aerosols, which means that the signal spreads out from the source in order to cover an extensive area and accurate alignment of the beam is not needed.
Sun, Ooi, Alouini and coworkers are presently producing high-performance UV-LED sources and extremely sensitive detectors capable of receiving UV signals accurately and quickly. In their recent work, they made use of an LED for sending pulsed UV-B signals to a sensor containing two antireflective lenses capable of collecting and focusing the UV-B light into a photodetector. Strong power transmission was observed by the team even when the angle between detector and source was increased up to 12 degrees, thus proving that direct line-of-sight was not needed. Additionally, the system was also able to transmit data at a record-breaking rate of 71 megabits per second (Mbps).
"Other groups have used different types of UV sources for transmitting relatively slow NLOS signals for communications," says Ooi. "We are the first to achieve multiple tens of Mbps transmission using UV-B LEDs."
With their concept being successfully proved in a low-power system, the team now plans to increase the optical power and sensitivity till they attain long-distance nonline-of-sight UV communications along with high data transmission rates.
"These interdisciplinary collaborative efforts between the photonics and communication theory groups at KAUST are paving the way toward the next frontier for optical wireless communication systems," states Alouini.