'Twisted' waves could boost capacity of wi-fi and TV
Published: 2nd Mar 2012 08:20:48
A striking demonstration of a means to boost the information-carrying capacity of radio waves has taken place across the lagoon in Venice, Italy.
The technique exploits what is called the "orbital angular momentum" of the waves - imparting them with a "twist".
Varying this twist permits many data streams to fit in the frequency spread currently used for just one.
The approach, described in the New Journal of Physics, could be applied to radio, wi-fi, and television.
The parts of the electromagnetic spectrum that are used for all three are split up in roughly the same way, with a spread of frequencies allotted to each channel. Each one contains a certain, limited amount of information-carrying capacity: its bandwidth.
As telecommunications have proliferated through the years, the spectrum has become incredibly crowded, with little room left for new means of signal transmission, or for existing means to expand their bandwidths.
But Bo Thide of Swedish Institute of Space Physics and a team of colleagues in Italy hope to change that by exploiting an entirely new physical mechanism to fit more capacity onto the same bandwidth.
The key lies in the distinction between the orbital and spin angular momentum of electromagnetic waves.
A perfect analogy is the Earth-Sun system. The Earth spins on its axis, manifesting spin angular momentum; at the same time orbits the Sun, manifesting orbital angular momentum.
The "particles" of light known as photons can carry both types; the spin angular momentum of photons is better known through the idea of polarisation, which some sunglasses and 3-D glasses exploit.
Just as the "signals" for the left and right eye in 3-D glasses can be encoded on light with two different polarisations, extra signals can be set up with different amounts of orbital angular momentum.
Prof Thide and his colleagues have been thinking about the idea for many years; last year, they published an article in Nature Physics showing that spinning black holes could produce such "twisted" light.
But the implications for exploiting the effect closer to home prompted the team to carry out their experiment in Venice, sending a signal 442m from San Giorgio island to the Palazzo Ducale in St Mark's square.
"It's exactly the same place that Galileo first demonstrated his telescope to the authorities in Venice, 400 years ago," Prof Thide told BBC News.
"They were not convinced at all; they could see the moons of Jupiter but they said, 'They must be inside the telescope, it can't possibly be like that.'
"To some extent we have felt the same (disbelief from the community), so we said, 'Let's do it, let's demonstrate it for the public.'"
In the simplest case, putting a twist on the waves is as simple as putting a twist into the dish that sends the signal. The team split one side of a standard satellite-type dish and separated the two resulting edges.
In this way, different points around the circumference of the beam have a different amount of "head start" relative to other points - if one could freeze and visualise the beam, it would look like a corkscrew.
In a highly publicised event in 2011, the team used a normal antenna and their modified antenna to send waves of 2.4 GHz - a band used by wi-fi - to send two audio signals within the bandwidth normally required by one. They repeated the experiment later with two television signals.
Crowds were treated to projections beamed onto the Palazzo Ducale explaining the experiment, and then a display of the message "signal received" when the experiment worked.
Prof Thide said that the public display - "in the style of (radio inventor) Guglielmo Marconi... involving ordinary people in the experiment", as the authors put it - was just putting into practice what he had believed since first publishing the idea in a 2007 Physical Review Letters article.
"For me it was obvious this would work," he said. "Maxwell's equations that govern electromagnetic fields are... the most well tested laws of physics that we have.
"We did this because other people wanted us to demonstrate it."
Prof Thide and his colleagues are already in discussions with industry to develop a system that can transmit many more than two bands of different orbital angular momentum.
The results could radically change just how much information and speed can be squeezed out of the crowded electromagnetic spectrum, applied to radio and television as well as wi-fi and perhaps even mobile phones.
At 16:25:41 in EnglandA waste partnership set up to save money for Dorset's councils is expected to overspend its budget by £2m.
At 16:17:17 in EnglandA Grade II-listed pier has reopened to the public after a £850,000 resurfacing and repair project.
At 16:07:54 in WalesThe boss at Wrexham's Glyndwr University has announced he is to stand down next year.
At 15:59:44 in EnglandTaxi drivers have received an apology from Milton Keynes Council over claims a letter suggested they were to blame for a rapist getting a licence.
At 15:58:53 in WalesHollywood star Michael Sheen has said plans to use culture to eradicate poverty in Wales do not go far enough.
At 15:56:33 in SportGrimsby Town have signed Rotherham United midfielder Nicky Walker on loan until the start of January.
At 15:54:43 in ScotlandSandwiches are returning to the menu of Aberdeen primary schools as the council reviews a decision to withdraw them.
At 15:52:19 in HeadlinesOur selection of some of the best news photographs taken around the world this week.
At 15:50:37 in EnglandTributes have been paid to two men from Plymouth who died in Amsterdam after reportedly snorting white heroin.
At 15:50:10 in ScotlandA speeding driver who killed two women on a pedestrian crossing in Fife has been jailed for almost five years and banned from driving for a decade.
Harvard CitationBBC News, 2012. 'Twisted' waves could boost capacity of wi-fi and TV [Online] (Updated 2nd Mar 2012)
Available at: http://www.ukwirednews.com/news/1415305/039-Twisted-039-waves-could-boost-capacity-of-wi-fi-and-TV [Accessed 28th Nov 2014]
News In Other Categories
A former grammar school vice principal has been given a suspended sentence after he admitted indecently assaulting three female pupils.
Grimsby Town have signed Rotherham United midfielder Nicky Walker on loan until the start of January.
The Indian economy grew at an annual pace of 5.3% in the three months to the end of September, down from 5.7% in the previous quarter, figures show.
Sandwiches are returning to the menu of Aberdeen primary schools as the council reviews a decision to withdraw them.
Sony has developed a watch made from e-paper as part of an initiative to experiment with the use of the material for fashion products.
Spending on front-line policing in England is set to fall by a fifth in the next five years, according to the London School of Economics (LSE).