'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 94.

    42 Minutes ago

    I love it when these so called scientists need to admit they dont know it all after all. Actually they know NOTHING. Only GOD knows how the universe works because HE made it

    Now admit the EVOLUTION is just another lie you made up like all the others


    Get off the internet and into therapy.

  • rate this

    Comment number 93.

    What does a low class news paper knows about electro magnetics and spin states of photons? Did you not find any other topic to begrudge? Let the scientists talk about it and come up with a consenses? It doesn't mean that when a set of British scientists rejects a theory, it becomes invalid forever.

  • rate this

    Comment number 92.


    whilst I agree with you on the absence of a deity. isn't the point of science to not dismiss anything until it is disproven beyond doubt.

    The books can be proven/disproven but when you have an invisible unseeable force which may or may not move in mysterious ways, there is no proof either way and therefore as a hypothesys, god can not be dismissed.

    newly realised agnostic

  • rate this

    Comment number 91.

    RogerGod; All of them! Why not? Let's have a party!!!!

  • rate this

    Comment number 90.

    so what would this imply for application?
    almost certainly means it wont work in practice.
    thats why it take an engineers word over a scientists any day (plus a little professional bias :-))
    we say ' if it aint broke dont fix it'
    they calculate how long it takes to boil a kettle on a block of ice.
    if both groups built a plane, which would you want to fly in?

  • rate this

    Comment number 89.

    usedtobeBill (No 79).
    Experiments don't prove, they disprove, by design! That's why they don't form part of religion. Any such experiment would have to adopt the premise that it's possible to disprove God's existence.

  • rate this

    Comment number 88.

    I had to chuckle at the heaven howlers input to this discussion. One thing you missed guys; none of you mention which religion you subscribe to, so we don't actually know which god or gods you want the credit to go to!

  • rate this

    Comment number 87.

    I cannot beleive my undeniable wit was removed! Boo-hiss to the moderators! I label ye heathens!!!

  • rate this

    Comment number 86.

    I'd be the first to put up my hand and say "huh?" when given the technical details but at the end of the day it will either work or it wont.
    And it wont work until everything can be done to try it.

    And if if it still doesn't... well they still will have learned something.

    That's what practical science is all about.

  • rate this

    Comment number 85.


    Scientists know they dont know everything. Religious people are certain that religion knows everything.

    You really must get out more and read things other than the fairy stories in the religious texts created by man for the control of the feeble minded.

  • rate this

    Comment number 84.

    Progress is being smart enough to think new ideas and brave enough to test them to destruction. Well done to all those hidden heroes, those scientist who dedicate their lives to possible hypothesys even though they know that one day they may well disprove all their lifes work.

  • rate this

    Comment number 83.

    To clarify my last comment on request: In all possible timelines which could have or will have happened as a result of our universe beginning, you are deluded, 70. I daresay if you folded our point in the 7th dimension through the 8th dimension to another point, you would still be crazy. Aka in another parallel infinity created from another starting point in reality, you would be mad.

  • rate this

    Comment number 82.

    I havent got my head fully around what both sides are trying to prove or disprove, but I more than approve that they are advancing knowledge, whichever side pans out to be proven as correct.

    Question everything!

    If it was left to others who fear the truth and fear knowledge, we would probably still believe the earth is the center of the universe, flat, and only about 4,000 years old.

  • rate this

    Comment number 81.

    so you think that there is some credibility issue with ther few 1000's of engineers responsible for developing the tech that makes, amongst other things, this forum work?
    referring to the ops manual for the human being it quite clearly says, section 1, chapter 1, para 1, clause 1:
    'please ensure brain is engaged prior to putting mouth in gear'

  • rate this

    Comment number 80.

    I don't know if it work or not, but the fact people are trying to develop new ideas and progress is to be applauded. However, town cryers, semaphore and beacons still work. Cave painting has a lot going for itself as well.

    Ah progress, dont you just hate it!!! :-)

  • rate this

    Comment number 79.

    I love it when these so called scientists need to admit they dont know it all after all. Actually they know NOTHING. Only GOD knows how the universe works because HE made it
    At least science is based on hypotheses and proven facts from experimentation. Uncertainties are inherent within that.
    And, if God did create everything, there's no harm in questioning how!

  • Comment number 78.

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

  • rate this

    Comment number 77.

    3 Minutes ago
    Is it just me or is deny nothing a complete nutter lol

    (or he/she is from the BBC to drum up participation in this HYS!)

  • rate this

    Comment number 76.

    @ 33. Under-Used

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

    I guess the original poster must mean orbital/spin angular momentum in the quantum mechanics sense that most engineers wouldn't usually know about.

  • Comment number 75.

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


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