“Twisted” light to make fiber-optic cables obsolete?

Researchers have taken an important step towards using “twisted” light as a form of wireless, high-capacity data transmission which could one day make fiber-optic cables obsolete. In a recent paper in the journal Science Advances, a team of physicists based in the U.K., Germany, New Zealand and Canada describe how new research into what’s called optical angular momentum (OAM) could overcome current limitations of wireless communications.

Scientists can “twist” photons—individual particles of light—by passing them through a special type of hologram, similar to that on a credit card, giving the photons a twist known as optical angular momentum.

While conventional digital communications use photons as ones and zeroes to carry information, the number of intertwined twists in the photons lets them carry additional data – something akin to adding letters alongside the ones and zeroes. The ability of twisted photons to carry additional information means that optical angular momentum has the potential to create much higher-bandwidth communications technology. OAM techniques have been used to transmit data across cables, but transmitting twisted light across open spaces has been significantly more challenging. Even simple changes in atmospheric pressures can scatter light beams and cause the spin information to be lost.

The researchers examined the effects on both the phase and intensity of OAM carrying light over an actual link in an urban setting to assess the viability of these modes of quantum information transfer. Their free space link, in Erlangen, Germany, was 1.6-km in length and passed over fields and streets and near high-rise buildings to accurately simulate an urban environment and atmospheric turbulence that can disrupt information transfer in space.

Field tests revealed new challenges that must be overcome before systems can be made commercially available, according to the report. Previous studies had indicated the potential feasibility of OAM communication systems, but had not fully characterized the effects of turbulent air on the phase of the structured light propagating over links of this length.

Dr. Martin Lavery, head of the Structured Photonics Research Group at University of Glasgow, is the lead author on the team’s research paper. Lavery said, “In an age where our global data consumption is growing at an exponential rate, there is mounting pressure to discover new methods of information carrying that can keep up with the huge uptake in data across the world.

“A complete, working optical angular momentum communications system capable of transmitting data wirelessly across free space has the potential to transform online access for developing countries, defense systems and cities around the world. Free space optics is a solution that can potentially give us the bandwidth of fiber, but without the requirement for physical cabling,” said Lavery.

This study takes vital steps towards high-dimensional free space optics that can be a cheaper, more accessible alternative to buried fiber-optic cable, he continued. And it indicated the challenges future adaptive optical systems will be required to resolve. With these new developments, researchers are confident that they can now try new approaches to adaptive optics systems, Lavery added. “We are getting ever closer to developing OAM communications that can be deployed in a real urban setting.”

Dr. Lavery undertook the work in partnership with researchers from the Max Planck Institute for the Science of Light and Institute of Optics, and the Universities of Otago, Ottawa and Rochester. These findings allow researchers to address challenges not previously observed. The results may help them develop adaptive optics for quantum information transfer—and move closer towards a new age of free space optics that will eventually replace fiber optics as a functional mode of communication in urban environments and remote sensing systems.