'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 134.

    Well, it would seem that 'the proof is in the pudding', although it's good to see some debate as there are obviously some ideas 'on paper' that have problems materialising in the 'real' world. I do have to have a chuckle about the 'Physicists on one side and the Engineers on the other' as both parties tend to have a good grasp of the others' subject anyway. Time will tell...

  • rate this

    Comment number 133.

    This is all getting very worrying, soon they'll think of say, cold fusion or maybe faster than light speed transmission; where's it all going to end - with a Higgs bosunthingummy??

  • rate this

    Comment number 132.

    Entanglement is the solution. Exploit this phenomenon and the electromagnetic spectrum will only apply in the conversion of the data.

  • rate this

    Comment number 131.

    So if they can increase the data capacity of digital television transmissions, for example, I will be able to watch such wonderful shows on Dave 25 channel. Sheer bliss!

  • rate this

    Comment number 130.

    I'm a Physicist, and I have trouble understanding the two sides of the argument, so it's nice to see that this piece has focused more on the fact that public debate is taking place than on trying to explain the two sides.
    I just hope that the outcome doesn't damage the reputations of those who are wrong this time.

  • rate this

    Comment number 129.

    It is good that there are debates going on in the world of science. This means that known facts in science are constantly being scrutinised and challenged. But, debates =/= bickering. Let them do research. Then look over it and repeat any testing (if possible). Then they can make a judgement on whether it is valid or not.
    Debates are a good sign in science, it shows it is advancing.

  • rate this

    Comment number 128.

    5. MSP1

    "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."

    Your description is how science should work! Recently, however, it seems that just making stuff up and talking about it in an authoritative way is common.

  • rate this

    Comment number 127.

    The people who claim that this is a breakthrough don't sound very rational to me. The responses they're giving to all of these counterarguments seem to be along the lines of 'you are ignorant, we are not'. That isn't a scientific retort; it looks more like simply having a petulant tantrum because people were sceptical. That makes me rather sceptical, too.

  • rate this

    Comment number 126.

    As very few people are qualified to know which of these sides, engineers or physicists is correct, this seems a bizarre topic for a "have your say".

    I'm sure there must be a few other more suitable stories out there.

  • rate this

    Comment number 125.

    Are these some of the same tree huggers who are stopping the exploitation of Shale Gas.

  • rate this

    Comment number 124.

    When I first read about this, I was pretty sceptical like the engineers. However, what's the point of bad mouthing something that you feel won't work? Let them do their research, and let them find out what the outcome is. It's not going to effect those who say it won't work, and the researchers can continue on with their research either way. Bickering achieves nothing.

  • rate this

    Comment number 123.

    the way my BT internet performs - i think they have already twisted the signals

  • rate this

    Comment number 122.

    119. Basically, telecoms uses polarisation to double optical rates. The physicists have figured that you can use OAM to double rates. But the same laws of physics apply otherwise we'd have infinite states of polarisation already. The engineers have studied this already, the physicists (thinking they'd discovered a miracle) doubled their rate. They now look to triple rates from this discovery... ^

  • rate this

    Comment number 121.

    This appears very much like two competing universities bickering over a potentially lucrative discovery: One trying to disrepute the other who are understandably coy about releasing 'trade secrets' to a world where others may exploit their hard work for profit.
    Scientific process is for good reason. Profit will ensure science goes the way of politics with less than altruistic intent.

  • rate this

    Comment number 120.

    so come on which of the many gods is that
    dont believe in what your god gave you eyes ears mind hands believe in a book man gave you and has changed so many times when science has proved it wrong time after time.
    science demands proof, religion demands blind fools

  • rate this

    Comment number 119.

    116. Is the same kind of limitation as with quadrature amplitude modulation (albeit with degrees of spin as opposed to a phase/amplitude constellation)? If so I can see what you're getting at.

  • rate this

    Comment number 118.

    Good article, it was nice to have so many links/citations.

  • rate this

    Comment number 117.


    Meme Alert!

    The flat earther meme was invented In 1828 by American writer Washington Irving in his 'biography' of Columbus.. which included a meeting where Columbus was criticised by establishment figures because they believed the earth was flat.. fiction, not fact.. the meeting and what transpired where entirely invented by Irving.

  • rate this

    Comment number 116.

    111. Not quite; the physicists published their grand claim after successful bi-modal transmission with OAM. What they didn't realise is that this is already common practice in telecommunications almost identical to circular polarisation. We can already double data rates with polarisation. We can't triple due to the limitations of physics, which the engineers understand. The same laws apply here.

  • rate this

    Comment number 115.

    Whoever turns out to be right, we will have learned something.
    Meanwhile, back to the duel: Physicists v. Engineers.
    Pocket calculators at 20 paces...

    RE: 82. "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."

    Unfortunately, some still do.


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