News in Science

Twisted light may boost internet bandwidth

Bandwidth breakthrough A new fibre optic technology could increase internet bandwidth capacity by sending data along light beams that twist like a tornado rather than move in a straight line, say scientists.

The discovery comes as internet data traffic is reaching its limit amid mounting demand for bandwidth by users of smartphones and internet-enabled devices, creating problems for network providers.

The new technology uses optical vortices, which are like doughnut-shaped laser light beams. Also known as orbital angular momentum (OAM) beams, they were thought to be unstable in fibre until now.

An engineering professor at Boston University, Siddharth Ramachandran, found a way to make an optical fibre that can handle them.

The technique is described in the US journal Science.

"Our discovery, of design classes in which they are stable, has profound implications for a variety of scientific and technological fields," said Ramachandran.

"Including the use of such beams for enhancing data capacity in fibres."

Optical communication system expert and co-author Alan Willner at the University of Southern California says the fibre is a "very unique and valuable innovation."

Traditionally, bandwidth has been enhanced by increasing the number of colours, or wavelengths of data-carrying laser signals -- essentially streams of 1s and 0s -- sent down an optical fibre, where signals are processed according to colour.

Increasing the number of colours -- or channels -- has worked well since the 1990s when the method was introduced, but now that number is reaching physical limits.

An emerging strategy to boost bandwidth is to send the light through a fibre along distinctive paths, or modes from one end of the fibre to the other. Unlike the colour channels, data streams of 1s and 0s mix together so determining which stream data comes from requires computationally intensive and energy-hungry algorithms.

Ramachandran and Willner's approach combines both techniques packing several colours into each mode and uses several modes. But unlike conventional fibres, the data streams remain separate at the receiving end.

Using this technique, they showed it was possible to send a huge amount of data through a one-kilometre fibre, as much as 1.6 terabits per second, or the equivalent of transmitting eight Blu-Ray DVDs every second.

Paradigm shift

The work is a "paradigm shift", comments Professor Ben Eggleton, director of the Centre for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS) at the University of Sydney.

"The challenge is at the moment we're running up against a bottleneck," says Eggleton.

For some time now engineers have been trying to find ways of getting more bandwidth in the fibre rather than put more fibres in.

"Traditionally we have done things like wave length multiplexing where we just keep on adding channels and frequency space but you run out of bandwidth.

"This [new technique] is like another degree of freedom that gives you more bandwidth in that single mode fibre which might allow you to increase the capacity by another factor of 10.

That's worth a huge amount of money, and has incredible benefit," says Eggleton.

But, he says, it may take some years for this technology to be deployed.

"It will require new fibre designs and new architectures to lay down the fibre."

"I don't think it's going to be part of the National Broadband Network, I think it's really looking at the next generation of roll out.

"But we need breakthroughs like this."