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'Twisted' waves could boost capacity of wi-fi

American and Israeli researchers have used twisted, vortex beams to transmit data at 2.5 terabits per second. Its of the capacity of more than 66 DVDs - per second. This technique is likely to be used in the next few years to vastly increase the throughput of both wireless and fiber-optic networks.

The technique relies on manipulating what is known as the orbital angular momentum(OAM) of the waves. The striking demonstration of the approach, reported in Nature Photonics, is likely to lead to even higher rates. Angular momentum is a slippery concept when applied to light, but an analogy closer to home is the Earth itself.
Our planet has "spin angular momentum" because it spins on its axis, and "orbital angular momentum" because it is also revolving around the Sun.

Light can have both these types, but the spin version is the far more familiar, as what is commonly called polarisation, or the direction along which light waves wiggle. Polarising sunglasses and many 3D glasses work by passing one polarisation and not another.

In many data-carrying applications involving light, more data is packed on to light waves by encoding one polarisation with one data stream, and another with a different stream.
That means twice as much information can fit within the same "bandwidth" - the range of colours that the transmitting equipment is able to process.

How it works:

In this case, Alan Willner and fellow researchers from the University of Southern California, NASA’s Jet Propulsion Laboratory, and Tel Aviv University, twisted together eight ~300Gbps visible light data streams using OAM. Each of the eight beams has a different level of OAM twist. The beams are bundled into two groups of four, which are passed through different polarization filters. One bundle of four is transmitted as a thin stream, like a screw thread, while the other four are transmitted around the outside, like a sheathe. The beam is then transmitted over open space (just one meter in this case), and untwisted and processed by the receiving end. 2.5 terabits per second is equivalent to 320 gigabytes per second, or around seven full Blu-ray movies per second.

This huge achievement comes just a few months after Bo Thide finally proved that OAM is actually possible. In Thide’s case, his team transmitted an OAM radio signal over 442 meters (1450ft).

The next task for Willner’s team will be to increase the OAM network’s paltry one-meter transmission distance to something a little more usable. “For situations that require high capacity… over relatively short distances of less than 1km, this approach could be appealing. Of course, there are also opportunities for long-distance satellite-to-satellite communications in space, where turbulence is not an issue,” Willner told enthusaistically.

The future of wireless networking is very bright indeed, however.