'Twisted light' data-boosting idea sparks heated debate

Images of the phase of "twisted" light The "twist" of the waves has been put forward as a way to carry vast amounts of data

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An idea to vastly increase the carrying capacity of radio and light waves has been called into question.

The "twisted light" approach relies on what is called light's orbital angular momentum, which has been put forth as an unexploited means to carry data.

Now a number of researchers, including some formally commenting in New Journal of Physics, say the idea is misguided.

Responding in the same journal, the approach's proponents insist the idea can in time massively boost data rates.

That promise is an enticing one for telecommunications firms that are running out of "space" in the electromagnetic spectrum, which is increasingly crowded with allocations for communications, broadcast media and data transmission.

So others are weighing in on what could be a high-stakes debate.

"This would be worth a Nobel prize, if they're right. Can you imagine, if all communications could be done on one frequency?" asked Bob Nevels of Texas A&M University, a former president of the Institute of Electrical and Electronics Engineers' Antennas and Propagation Society.

"If they've got such a great thing, why isn't everyone jumping up and down? Because we know it won't work," he told BBC News.

The disagreement in New Journal of Physics provides a window on the time-honoured practice of open debate in academic journals (as opposed to the increasingly widespread approach of debating issues before they are even formally published): a kind of "he says, she says" with references.

Wiggle room

The principle behind the idea is fairly simple. Photons, the most basic units of light, carry two kinds of momentum, a kind of energy-of-motion.

One, spin angular momentum, is better known as polarisation. Photons "wiggle" along a particular direction, and different polarisations can be separated out by, for example, polarising sunglasses or 3D glasses.

Start Quote

This is not something invented by us, something we found out on a coffee break - this is on solid theoretical foundations ”

End Quote Bo Thide Swedish Institute of Space Physics

But they also carry orbital angular momentum - in analogy to the Earth-Sun system, the spin angular momentum is expressed in our planet spinning around its axis, while the orbital angular momentum manifests as our revolution around the Sun.

The new technique aims to exploit this orbital angular momentum, essentially encoding more data as a "twist" in the light waves.

That the phenomenon exists is not in question - it has been put to use recently in studying black holes, for example.

What makes the current debate devilishly complex is arguing whether experiments by Bo Thide of the Swedish Institute of Space Physics and colleagues really do use and benefit from it.

The team has carried out very public demonstrations of the idea, sending data across a Venice lagoon in a test first described in a New Journal of Physics article. But even before that article made it to press, other researchers were questioning the approach's validity.

In a paper in IEEE Transactions on Antennas and Propagation, Lund University's Ove Edfors and Anders Johansson argued that what was going on was a version of "multiple input, multiple output" - or Mimo - data transmission, a technique first outlined in the 1970s.

"I've been trying to have a discussion with these guys, asking for arguments - because all the arguments they have put forward have been perfectly explainable by standard theories," Prof Edfors told BBC News.

"What I get back is 'you don't understand, you're not a physicist', and I say 'well, try to convince me'."

Julien Perruisseau-Carrier at the Swiss Federal Institute of Technology in Lausanne, Switzerland (EPFL), and colleagues make much the same argument in their comment paper published this week. But it seems clear that the controversy arises as a conflict between the disciplines of physics and engineering.

"These people are physicists, they have their own research," Prof Perruisseau-Carrier told BBC News. "But the authors are trying to spin off some of their work into a telecommunications issue.

"Signal received" message projected on wall in Venice There was a "signal received" last year - but could vastly improved signal sizes be reached?

"The fact is they didn't understand that what they were doing, as we explained, is a subset of something very well-known and documented."

Detractors argue that the demonstrations so far have only used two "modes" to transmit information, perfectly replicating a Mimo setup - and that if Prof Thide and colleagues try to extend the work - to the promised tens or hundreds of possible modes, they will fail.

For his part, Prof Thide insists that it is the engineers who have misunderstood.

"The typical wireless engineer, even if a professor, doesn't know anything about angular momentum," he told BBC News.

"The points made by these people... are in contradiction to each and every textbook there is in electrodynamics. This is not something invented by us, something we found out on a coffee break - this is on solid theoretical foundations going back through several Nobel prizes."

But the groundswell of resistance to the technique seems to be growing. Prof Nevels and his Texas A&M colleague Laszlo Kish have published a paper in PLOS ONE that they believe is the simple, final proof of its impossibility - and more academics are signing on as co-authors.

Prof Perruisseau-Carrier says that the idea will prove itself valid or otherwise soon enough.

"They mentioned they have some contact with telecoms companies - we were very happy to see that. There's no doubt that as soon as they defer to a real expert, that people will notice [that the idea is flawed]," he said.

"We are convinced that this will not go anywhere."


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  • Comment number 74.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 73.

    "If it's such a god, efficient, simple idea, how come the inventors (Or discoverers) of radio waves didn't exploit them immediately?"

    Dunno: mybe they were British. Like those blokes who were studying microwaves and used their experiment to cook their own lunch without realising that pretty soon every kitchen would have one!
    (I rake it that your "god" was a Freudian typo!)

  • rate this

    Comment number 72.

    49. Eddy from Waring

    We stopped using AM years ago, we now use Frequency Division Multiplexing where multiple data streams are carried at different frequencies along the same fibre. The problem is we are limited to a narrow usable spectrum @ 1550 nm and being able to cool the lasers switching between 0 and 1 at very high speeds.

    If 'twisted light' does work that could resolve the spectrum issue.

  • rate this

    Comment number 71.

    Very interesting.
    I think the engineers are reasonable.
    The OAM-based optical transmission is actually a MIMO systems. While MIMO is well-established in wireless telecommunication, we do not have MIMO in optical communication systems currently.

  • Comment number 70.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 69.

    The usual anti-science comments. There is really not much to say on this article. Who knows why it has been opened up to HYS.

  • rate this

    Comment number 68.

    Drunken Hobo (52),

    “… How do you change the angular momentum of a photon anyway?”

    As photons are gauge bosons, and can attain a Bose–Einstein condensate state, it is ttheoretically possible to manage/manipulate/encode a message in the BEC while leaving the angular momentum of each photon unchanged.

  • rate this

    Comment number 67.

    I am unsure what we are required to comment on.

    Interesting concept, however, if this happens then the technology will be transparent to the end user.

    I use to use Radar and Radios, I was good at what I did, but someone a long time ago had worked out the science stuff behind it all, all I did was use it.

  • rate this

    Comment number 66.

    Reminds me of my days back in uni, for the scientists everything was theoritically posible given enought time, money and resources. The problem was us poor engineers never had the time, money or resources!

  • rate this

    Comment number 65.

    "Scientists disagreeing about something. This is cast-iron proof that the world is less than 10,000 years old..."

    This is the scientific method. See: http://en.wikipedia.org/wiki/Scientific_method
    If you want "facts", try religion.

    "And it does not increase the risk of human / animal cancers?"

    Another nutter!

    Where are all those billions spent on education going?

  • rate this

    Comment number 64.

    This story demonstrates how essential it is to have funding for blue sky research at our universities. The potential rewards are amazing.

  • rate this

    Comment number 63.

    53 GKH - It's literally the most stupid conspiracy theory there has ever been. One day, in the mid-2000s, a redneck looked up for the first time in history. He was confused as to what he saw - white trails coming out of big metal birds in the sky. What could these be? The answer was obvious; the government was spraying the population with evil chemicals!
    And so the "chemtrail" conspiracy started.

  • rate this

    Comment number 62.

    This is great science in action. In our 'must have it now' society we expect instant decisions / results / conclusions suitably dumbed down to yes or no. We see this to and fro debate/conflict as a problem. Scientific advances(or not) need to be viewed over a longer term and answers are rarely clear cut.

  • rate this

    Comment number 61.

    How does this affect the phlogiston ?

  • rate this

    Comment number 60.

    I can see why the physicists might view the engineers as having a problem, the physics are awesome.
    Is this OAM the property of photons found in Laguerre-Gaussian Light beams?
    Whether the photons can carry more information of not,( some researchers have been working on methods)I read that most optical fibres used today themselves alter the OAM state, so what would this imply for application?

  • rate this

    Comment number 59.

    'Nothing is impossible to the scientific mind'...That's what Peric in the 'Trigan Empire' said and I trust him!

  • rate this

    Comment number 58.

    55.David H Parry
    But only because big business is only interested in profits not social responsibility beyond shareholders and fat cat directors wages
    That will only change once all the money is in their hands and they realise they have no customers any more or the revolution comes along soon very soon i hope

  • rate this

    Comment number 57.

    And it does not increase the risk of human / animal cancers?

  • rate this

    Comment number 56.

    Scientists disagreeing about something. This is cast-iron proof that the world is less than 10,000 years old, evolution didn't happen, there's no global warming and that Obama is probably the anti-Christ, or at least his cousin.

  • rate this

    Comment number 55.

    How do we alter the angular momentum of a 'signal'?
    How much power is needed to do that?
    So some sort of multiplexer is needed at the transmitter end and some sort of demultiplexer is needed at the receiver end.
    How soon are we going to see them?

    I make a prediction; they'll be manufactured in China!


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