'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.

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"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 34.

    If they think they can do it, they should go for it. History is littered with great scientists who were scoffed at by the peers of their time. It's always easier to shoot holes in what others propose than to propose something yourself.

  • rate this

    Comment number 33.

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

    That's a strange and rather silly thing for a scientist to say. Angular momentum is not some mystifying phenomenon, and for a scientists to suggest that a laymen cannot gain a complete understanding of a scientific concept is just arrogant, even foolish.

  • rate this

    Comment number 32.

    What is the point of a topic which none of us ordinary folk know nothing about and the boffins are too busy to comment. Come on HYS lets have something decent to debate. Even Cameron's app is getting alow response. LOL

  • rate this

    Comment number 31.

    I like the naivety of some thinking academic science is apolitical and purely based on cold logic and evidence. I personal like this article for giving a genuine insight into the bickering world of academia.

    It is also worth pointing out that science is not black and white. "Proven" theories can still be wrong and not every scientific idea can be applied to the real world.

  • rate this

    Comment number 30.

    The following is also an interesting article about OOFDM/data (DAY-TAH and not DAH-TAH) handling . . .


  • rate this

    Comment number 29.

    I love HYS. It offers those of us with an opinion but no real understanding of the subject to pontificate as armchair experts. Frequently the more ignorant posts are highly amusing. So FWIW I think the number of people in the world actually qualified to post on this topic must be less than 1000.

    Has anyone mentioned that scientists shouldn't play God yet?

  • rate this

    Comment number 28.

    There is a long history of people who don't understand something claiming it is wrong. Quantum theory comes to mind, yet it has turned out to be one of the most successful theories in practice.

    If the researchers can demonstrate their theory and back it up with mathematics then all well and good. Then others can repeat the experiments. If they can't, it will join the likes of cold fusion.

  • rate this

    Comment number 27.

    If you were a physicist wanting to find a research project promising millions in corporate grants, the idea is perfectly feasible, as long as the government gives your company a tax break to pay for the research.

    If you were a customer paying 20% more for your current services to fund these tax breaks, you would see it for what it is - another RIP OFF in RIP OFF BRITAIN.

  • rate this

    Comment number 26.

    Who is right? Well that will be verified experimentally if they can extend the transmission over a dozen modes the engineers will be proved wrong if it can't be extended over to the physicists will be wrong, however I doubt they are, I think the engineers sound confused over the theory behind this. Time will tell.

  • rate this

    Comment number 25.

    With regard to overly simple implementations of complex processes; JVC had developed S-VHS to give much higher picture resolutions, with complex circuitry achieving the FM signal manipulation for S-VHS. However, Nokia achieved the same performance with just a handful of electronic components, in their ASO implementation of FM high resolution signal handling. Its a shame the Italians have failed.

  • rate this

    Comment number 24.

    And for whoever keeps voting down my (legitimate) comment about this being disproven: you really think the scientific community would go out of it's way to mock this idea - which would be immensely beneficial to modern society - just for fun or some kind of power trip?

    The conflict with the core physics laws means you prove this and we need to reconsider the majority of physics. UNLIKELY.

  • rate this

    Comment number 23.

    This is an excellent example of proper scientific debate, leading to truth & discovery by considered discussion between peers. It's a shame that some of it is done in the media, though.

  • rate this

    Comment number 22.

    Makes you wonder about all the radio telescopes listening for alien communication. The noise they currently hear could be the receipt of lots of alien communication. Its not straight horizontal or vertical waves but a complete mixture of different phrased modulation that we have yet to comprehend, yet even understand how it could be decoded.

  • rate this

    Comment number 21.

    100% agree with scientific testing of the theory. However, we will be waiting indefinitely for this one. The theory has already been completely disproved, so if we will insist on waiting until it has been proven to close the case... that is a long time.

  • rate this

    Comment number 20.

    "The points made by these people .....are in contradiction to each and every textbook"

    So were the 'points' made by Newton, Einstein and literally hundreds of other scientists and thinkers through the ages.

    A valid theory will be testable and, possibly, reproducible by others. There's little point in argument until this has been done.

  • rate this

    Comment number 19.

    I'm All in favour of increasing the amout of data that can be carried - it's better than my idea of filling a hundred memory sticks with info and flying them somewhere.

  • rate this

    Comment number 18.

    If there is a question of whether more than 2 "modes" will work or not then surely just let the experts get on and properly prove / disprove it - rather than having to read articles like this that only shows slightly silly posturing from all sides.

  • rate this

    Comment number 17.

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

  • rate this

    Comment number 16.

    ".. scientific principles .. put forward a theory or hypothesis and then the proof to back it up .. allow others to reproduce it or not" - Actually, the method is to observe / perform experiments, build one or more hypotheses, and then test predictions stemming from those hypotheses. Observation always comes first - a theory that does not fit the facts is incomplete at best and is probably wrong!

  • rate this

    Comment number 15.

    Lets twist again like we did last summer.


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