Terabits by Twisted Light: The Optical Communications Revolution
Jun 27, 2012 8:00 AM PT
Twisted infrared light beams have propelled wireless data transmission to a dazzling 2.56 terabits per second via a system developed by a multinational team of researchers led by the Optical Communications Laboratory at the University of Southern California.
The process, called "orbital angular momentum" (OAM) multiplexing, essentially twists beams of light so that they can carry more data, more quickly than ever before.
Broadband cable supports the transmission of around 30 megabits per second; this system transmits more than 85,000 times that amount.
The work of these scientists builds on prior OAM research by Leslie Allen, Anton Zeilinger, Miles Padgett and others.
"The basic ideas were out there," said Alan Willner, the Steven and Kathryn Sample Chair in Engineering at USC and one of the authors of the team's recent Nature Photonics article about the research.
"We just pushed things further," he told TechNewsWorld.
To accomplish the feat, Willner -- along with colleagues from NASA's Jet Propulsion Laboratory, China, Pakistan and Israel -- manipulated eight beams of light, twisting each one into a helical shape and sending it through free space to a receiver in the lab.
Twisted light beams are particularly powerful because they can encode tremendous amounts of data, and twisting them in various ways and directions only increases that data capacity. It far exceeds anything possible with radio frequencies such as those currently used for WiFi and cellular communications.
"With optics, you can encode more data than you can with radio waves," noted Willner.
Applications and Limitations
Before long, this research, which was funded by the Defense Advance Research Projects Agency (DARPA) as a part of the InPho (Information in a Photon) program, will find its way into a variety of applications, both in space and on Earth, predicted Willner.
"In the future, this will likely require a more cost-effective and integrated approach," he said. "Ours was a demonstration on a limited scale to show that you can do terabits."
At least in the near term, the technology's potential applications for terrestrial communications are limited, since it requires a clear line of sight and no turbulence or other interference.
"Even [on] a clear day, the turbulent atmosphere will distort the phase front of the light waves," Mohsen Kavehrad, the W. L. Weiss Chair Professor of Electrical Engineering at The Pennsylvania State University, told TechNewsWorld. "It is a bad idea to rely on phase manipulations for unguided atmospheric transmissions. [It] may be better to be used in vacuum."
Because of atmospheric issues, therefore, the process might be more practical in satellite and space communications than on Earth, since space has no turbulence, according to Moshe Tur, a professor of electrical engineering at Tel-Aviv University who helped to develop the ideas behind this work and contributed to the research.
"[This work] can find various applications where large amounts of data must be exchanged between two points and OAM multiplexing is technically and economically advantageous," Tur told TechNewsWorld. "Turbulence may hurt performance of such optical wireless links, which means that longer-range applications can succeed in space."
Just as promising is the possibility that OAM processes could be adapted to fiber optic cables, which are the basis of the Internet and most other terrestrial communications.
"OAM modes can play even a more important role in fiber-optic communications, where work on all forms of space-division multiplexing is currently a very hot research topic," noted Tur. "Preliminary results on long-range OAM transmission have already been reported."
There are many other potential applications of OAM data transmission, including medical imaging and even the detection of landmines.
"It's very exciting for a number a fields," IT consultant Bill St. Arnaud told TechNewsWorld. "There's a huge range of applications, once people start to realize its impact. It'll be a few years before the technology becomes commonplace, but the potential is significant."
OAM technology is so fundamental that it will likely change the ways researchers think about communications and imaging for generations, said St. Arnaud.
"It's one of those fundamental new technologies that will have an impact across a whole range of fields," he remarked. "It's like the discovery of electricity."