'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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  • rate this

    Comment number 14.

    So, we have;

    'A couple of blokes reckon they can do something clever with light. Pretty much everyone else thinks they're nutters!'

    Is this news? Would not that basic summary apply to almost every great discovery over time? Did Newton not have his detractors? Pythagoras too? What about Copernicus, Galileo and even Einstein?

    Time will tell.

    Nobel or not Nobel? That is the question.

  • rate this

    Comment number 13.

    I think what you guys are missing from the argument is that the public experiment showed what we already know and exactly what the theory behind this supports; you CAN send 2 modes in one light beam. However for no reason the team have summised that you can send an "infinite" number or just more than 2. This is a direct contradiction of the theory and physics laws which allowed their experiment.

  • rate this

    Comment number 12.

    Thanks BBC for not giving this subject the dumbed down 'Horizon treatment'. An excellent article.

  • rate this

    Comment number 11.

    can they not just put everything in to one large zip file? :P

  • rate this

    Comment number 10.

    The original team went for a very public demonstration, rather than sticking to cautious publication.

    Pons & Fleischmann paid dearly for similar arrogance.

    That doesn't make these guys right or wrong. In fact I hope they are right. But there's very good reasons for confining new findings to the usual mechanisms of academic discourse.

  • rate this

    Comment number 9.

    Wow, Sheldon and Howard are really getting into one......

  • rate this

    Comment number 8.

    I must say (as a failed mathematician and moderately successful engineer) that the equipment they described always seemed absurdly simple for the effect they were claiming to exploit.

    However, if a simple antenna redesign does produce the increase in bandwidth they posit, then it hardly matters whether their explanation is right or wrong. Except to future generations of patent lawyers, that is.

  • rate this

    Comment number 7.

    Seems like people are forgetting scientific principles which is to put forward a theory or hypothesis and then the proof to back it up and to allow others to reproduce it or not!

    Too many people twittering rubbish rather than rational thought. The modern world player looking for their 15 mins of fame however misplaced.

  • rate this

    Comment number 6.

    Congratulations Jason, for such a good attempt at explaining the substance of this argument. The BBC once again has a science/tech reporter who seems to really understand the science of the stories they report on. Yes, there really are important news stories that can't be dumbed-down, and which to understand and have a useful opinion of, you must have had a good science education.

  • rate this

    Comment number 5.

    Not sure what the point of this article is. It will all get resolved in the usual way. In science it is necessary to substantiate theories by experiment and observation. If your theory agrees with observations of how the universe actually works, then OK. If not, its wrong. This is different to the way things are in politics and the media where you just make stuff up and then talk about it a lot.

  • rate this

    Comment number 4.

    The debate is entirely science; the experiment carried out to date utilised 2 spatially orthoganal wave modes. This is already in use in radio etc brought about by circular polarisation. They have yet to transmit 3 modes at the same time.

    An antennae emitting energy in the way proposed would simply have to radiate more energy than it would absorb, violating the 2nd thermodynamic law.

  • rate this

    Comment number 3.

    I don't know how much money this will cost to test - so why not wait till it's tested before getting overexcited?

    If it turns out that the theory is right there's going to be a whole load of engineers looking completely stupid. They already have a hard enough time being taken seriously, for their sake I hope they're right on this one.

    Otherwise it's back into the corner with the D cap on.

  • rate this

    Comment number 2.

    The article, alas, provides no real detail of the disputed physics.

  • rate this

    Comment number 1.

    This debate is not science, there is no respect going on here. It appears that too many of these people are after media time. The best thing all parties can do is shut up and let the blokes from Sweden talk the companies to see if they can do it for real.

    Then the talking can begin.


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