'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 54.

    Eddy from Waring
    Its not principle its theory
    What they are claiming is not that they can put more data onto an em wave but they can put more em waves onto a single medium and use OAM rather than frequency to differentiate the streams However as photons due to wavelength have a non negligible size (size is greater than 0) you will always be limited by volume of the conductor less so than FM

  • rate this

    Comment number 53.

    50.BluesBerry --- The what now? Weather / mind control. What particular article did you actually read?

  • rate this

    Comment number 52.

    This reminds me of Clarke's First Law: "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."

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

  • rate this

    Comment number 51.

    48.Ian Tresman
    Science always makes up theories that are then either proved or disproved by experimentation its the way science works 99.9999% of the time.
    the great thing about science is peer review and that means open frank and frequently opposing views will debate the science (theories) and the experiments (physical) to come up with the real facts

  • rate this

    Comment number 50.

    I worry about these experiments.
    When we fool around with photons, we are fooling around with the very matrix of the orbital angular momentum, essentially encoding more data as a "twist" in the light waves. More data to speed information, or more data to control information? Physics + engineering have already led to weather manipulation/moderation, and some think aspects of mind control.

  • rate this

    Comment number 49.

    In principle, using simple everyday amplitude modulation, a single optical fibre could carry vastly more data than any practical system in fact does.

    Even if the physicists' claim that they have found a way to impose hugely more data on EM waves is correct (and I'm sceptical) similar practical problems would almost certainly present themselves.

  • rate this

    Comment number 48.

    Science should be able to decide this, not the views of a bunch of physicists before the experiments have been done.

  • rate this

    Comment number 47.

    translated it means"we got our wires twisted"

  • rate this

    Comment number 46.

    I dont think many people who have any understanding of Higher level physics would disagree that by using spin it is a form of mimo transmission however it is very different in so much as it does not need to take up massive extra amounts of the spectrum like multimode lasers do however both suffer the same limitation of the transportation media and it's saturation levels.

  • rate this

    Comment number 45.

    While studying computing at university, a passionate lecturer told us about maximising data transfer. He said experiments had used polarisation (changing the angles of light particles, like what is used in 3D TV). They sent the equivalent of all of Northern Europe's daily telephone calls around the world, down 1 strand of fibre, in 1 second.

    A bit of investment and we'd have no data problems!

  • rate this

    Comment number 44.

    The paper that criticizes the orbital angular momentum in radio is posted on vixra, a notorious crackpot-hosting website (you'll find papers on anti-gravity...). Anyway, OAM obeys an uncertainty principle similar to the Heisenberg one, the partition function of blackbody radiation with OAM states is exactly the same as radiation without OAM states. So the 2nd law of thermodynamics is not violated.

  • rate this

    Comment number 43.

    Never heard of this during my Communications Engineering and degree history, I'm sceptical and think investors would be aware or the huge risk to their money. Also, the electromagnetic Spectrum has been sold off and given away too cheaply for economic reasons for 4G which I think is a waste of radio spectrum for simply watching TV and video over wireless.

  • rate this

    Comment number 42.

    'Twisted light' data-boosting idea sparks heated debate.

    Not in my household.
    I'm just trying to afford to heat my house!
    But then again, that topic isn't sexy enough for the BBC journos.
    Some of the topics on this site are about as interesting as BBC2..

  • rate this

    Comment number 41.

    This passionate debating among 'specialists' is what makes all of this so interesting - in my own industry I come across the same blinkered, stonewall attitude as they fight to desperately protect their own little patch of hard won, scared turf. Breaking with accepted convention makes for superb problem solving and the blossom of innovation.

  • rate this

    Comment number 40.

    mr_befuddled said:
    "Have you tried reading the papers linked to from the article?"

    That's a fair point, sir, but I wish the article gave a better understanding of the disputed science, rather than just the disputing scientists.

  • rate this

    Comment number 39.

    Science doesn't have an ego. It doesn't claim to be definitive, just evidential. If one fact-based theory disproves another, this is welcomed and cross-examined. Unlike religion, which closes itself off and just calls you names if you don't believe in it. I know which I consider more reliable.

  • rate this

    Comment number 38.

    As a non-scientific person but a user of technology, I see how far scientific progress has come in my lifetime. In the 1960's, Capt. James T. Kirk was talking to the Starship Enterprise from a small gadget held in his hand - look where were reality is now.

    There are many things we still do not know about physics but the question is can we ever "bend" the laws of physics to suit our needs?

  • rate this

    Comment number 37.

    Whether or not it works in the way that some think it will (or won't) is not relevant.
    Just read the story of an Oz scientist who was investigating mini Black Holes at the single atom level (do they exist?). Ended up inventing WiFi. Not the first time that a scientist inventing one thing, ends up with something completely different (eg Fleming's penicillin).
    Keep investigating 'twisted light'!

  • rate this

    Comment number 36.

    Well well guys i like the fact that there are some negative points on here regarding this theory, there were even negative points being put across during the splitting of the atom (and guess what we did it),

    Negative Criticism always follows when humanity is on the brink of something new... and we do it coz we are scared

  • rate this

    Comment number 35.

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

    Yes it does! Have you tried reading the papers linked to from the article? And the references in those papers?

    It's all there.


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