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"Twisted" OAM Beams Carry 2.5 Terabits Per Second 142

Posted by samzenpus
from the greased-lightning dept.
MrSeb writes "American and Israeli researchers have used twisted, vortex beams to transmit data at 2.5 terabits per second. As far as I can discern, this is the fastest wireless network ever created — by some margin. These twisted signals use orbital angular momentum (OAM) to cram much more data into a single stream, without using more spectrum. In current state-of-the-art transmission protocols (WiFi, LTE, COFDM), we only modulate the spin angular momentum (SAM) of radio waves, not the OAM. If you picture the Earth, SAM is our planet spinning on its axis, while OAM is our movement around the Sun. Basically, the breakthrough here is that researchers have created a wireless network protocol that uses both OAM and SAM. In this case, Alan Willner and fellow researchers from the University of Southern California, NASA's Jet Propulsion Laboratory, and Tel Aviv University, twisted together eight ~300Gbps visible light data streams using OAM. For the networking nerds, Willner's OAM link has a spectral efficiency of 95.7 bits per hertz; LTE maxes out at 16.32 bits/Hz; 802.11n is 2.4 bits/Hz. Digital TV (DVB-T) is just 0.55 bits/Hz. In short, this might just be exactly what our congested wireless spectrum needs."
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"Twisted" OAM Beams Carry 2.5 Terabits Per Second

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  • by Anonymous Coward
    I do not like them, SAM I am.
  • by Jonathan_S (25407) on Monday June 25, 2012 @09:48AM (#40438027)

    This is very cool, but the current super high bandwidth demonstration is being done with optical light over very short (1 meter) distances.

    The article did point to an article from a couple months ago about the first ever OAM transmission; which was done with radio waves. But the antennas used look very directional and there was no mention of bandwidth.

    Optical might be useful to further increase the speed of fibers, and highly directional radio might help for satellite broadcast or to compete with microwave relay towers. But requiring highly directional antennas, on both ends, isn't good for mobile wireless.

    Hopefully we'll see another story soon where someone figures out how to detect and transmit OAM encoded radio waves from non-directional antennas.

    • by Shavano (2541114) on Monday June 25, 2012 @10:01AM (#40438167)
      No it's not practical over significant distances. Those different polarization states (that's what they are) are nor mathematically independent so there is a lot of ISI. You can only trade higher throughput for loss of SNR. 95 BPS per Hz is impressive but it can only be done in the most tightly controlled conditions. It will never be done in anything other than point to point links with very strong signal. Moreover, OAM is a buzzword without a clearly defined physical mechanism. EM waves have frequency and polarization and phase. Their "orbital angular momentum" is some combination of these parameters so you can't increase bandwidth over what can be done using some combination of these.
      • EM waves have frequency and polarization and phase. Their "orbital angular momentum" is some combination of these parameters so you can't increase bandwidth over what can be done using some combination of these.

        That was my take on this the first time I heard about it -- although my breakdown was E and M magnitude and direction. But the further discussions I read, and now this demonstration, seem to indicate otherwise.

        BTW, frequency and phase aren't exactly independent, are they?

      • Re: (Score:2, Informative)

        by IWannaBeAnAC (653701)
        Sorry, that whole post is nonsense! OAM is a clearly defined mechanism, and the different OAM states are orthogonal. See for example http://physics.aps.org/story/v17/st15 [aps.org] for an explanation.
        • Re: (Score:3, Informative)

          by Prune (557140)
          Peer reviewed IEEE paper proving grandparent is correct, you a troll, and OAM a scam: http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120 [lub.lu.se]
          • by TheSync (5291)

            Is it really a scam, or is it just that it can be implemented with MIMO?

            The paper states "we conclude that communicating over the sub-channels given by OAM states is a subset of the solutions offered by MIMO, and therefore does not offer any additional gains in capacity."

            All the practical implementations of OAM have been implemented with multiple antennas, so perhaps this is no big surprise.

            That said, the OAM demos have gotten satellite folks to wake up, perhaps they need to consider more generalized MIMO s

            • by TheSync (5291)

              Oh this kind of sucks though:

              "The helical phase of the OAM states remain coherent over vast distances, but the amount of energy that can be received beyond the Rayleigh distance with a limited-size array decays rapidly, as compared to free space attenuation, for all but OAM state 0."

      • EM waves have frequency and polarization and phase. Their "orbital angular momentum" is some combination of these parameters so you can't increase bandwidth over what can be done using some combination of these.

        Actually, I don't think their OAM is a combination of those parameters. It's about the spatial distribution of the phase around the axis of transmission.

        • by Viol8 (599362)

          Axis of transmission? That'll be polarisation. And phase - which I believe the OP mentioned.

          Sorry, I'm obviously missing the magic pixie dust property of EM waves here that hasn't been mentioned.

          • by Hettch (692387)
            Nope, its more than just polarization. The OAM (or whatever they're calling this) is a physical property of a ray of light transmission, and it manifests itself by spreading the energy out spatially away from the 'center.' You can "de-OAM" the transmission by spatial movement of your receiving array, so it is computationally less complex. However, it is _highly_ directional, and I have yet to see a decent analysis that involves multipath or other scattering interference. This is a mode of light that is not
            • by Prune (557140)
              That's a load of bullshit and peer reviewed IEEE paper proves it: http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120 [lub.lu.se]
              • by Hettch (692387)
                I looked for something like that when the Italian demonstration first got passed around, but couldn't find anything. I will retort by saying that it is indeed not "bullshit" after a first pass-through, this paper agrees with what I explained, however, this paper explains that it is not necessarily a new phenomena, but rather a special case. Thanks for the article though, I'll look at this more closely when I get a chance. But for clarification, what claim is the load of bullshit?
      • by Prune (557140)
        Mod parent up! OAM has been discredited in peer-reviewed IEEE paper: OAM has been discredited in peer reviewed IEEE published paper: http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120 [lub.lu.se]
    • Re: (Score:2, Funny)

      by Anonymous Coward

      Remember the IR data port fad? Thank Jebus THAT never took off. Not for lack of hype, either...

    • by Rei (128717)

      The problem here is that visible light doesn't pass through walls and that the range is short, not that it's directional. I don't see what's wrong with directional, so long as the direction of the antenna can be rapidly digitally reconfigured (and yes, such antennas exist). Seems an obvious way to free up spectrum in the future - data is only being transmitted (apart from weak sidebands) in the direction it's needed.

      The obvious downside you'll get to is that you'll *normally* have a clear line of sight, b

    • by Prune (557140)
      OAM has been discredited in peer reviewed IEEE published paper: http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120 [lub.lu.se]
  • Lasers vs wireless (Score:5, Interesting)

    by Anonymous Coward on Monday June 25, 2012 @09:48AM (#40438029)

    From the article: "fastest wireless network ever created". Since this thing uses lasers and requires line of sight it would perhaps be more relevant to compare to other laser transmission schemes, where the record stands at 26 Tbit/sec

    • Re: (Score:2, Informative)

      by Anonymous Coward

      But laser (I'm assuming optical or IR) uses higher frequency carrier wave. That makes it easier to transmit more data per second. The real achievement here is not bits per second; it's bits per hertz. When OAM is applied to those frequencies, it'd be able even transmit even more.

    • by steelfood (895457)

      Since this thing uses lasers

      Why are you bringing up sharks?

  • by Anonymous Coward
    Awesome, I've been saying for years that OAM would win!

    (But then again, I always root for the OAM beam!)
    • Re: (Score:2, Funny)

      by Anonymous Coward

      Let us root, root, root for the OAM beam,
      If they don't spin it's a shame.
      For it's one, two, three terabits,
      In a per second frame."

  • by mbone (558574) on Monday June 25, 2012 @09:53AM (#40438069)

    http://iopscience.iop.org/1367-2630/14/3/033001/pdf/1367-2630_14_3_033001.pdf [iop.org]

    I am still not sure exactly what the physics is here.

    • It's using the spatial variation of the signal. In cylindrical coordinates (r,theta,z) aligned with the axis of transmission z, it uses different phases at different thetas. In particular, a bunch of superposed signals each with phase varying around the z axis as cos(i*theta) for i=0,1,2,... should stay conveniently distinct from transmitter to receiver.

      I think the axis of transmission is baked into the idea pretty deeply - it's inherently unidirectional. I also think it's not robust to superposition: anoth

    • by jo_ham (604554)

      More like chemistry, actually when discussing the EM spectrum like this. Although the two sort of blur together when it comes to this sort of thing. The mathematicians would probably claim we were both just applied maths folks (a la xkcd comic).

    • by Prune (557140)
      That paper and OAM in general has been thoroughly discredited by a peer reviewed IEEE paper: http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120 [lub.lu.se]
  • by P-niiice (1703362) on Monday June 25, 2012 @09:55AM (#40438101)
    Cool! I can hit my monthly cap in .0001 seconds!
  • by Anonymous Coward

    Cross the streams!

  • by Anonymous Coward

    Two reasons:
    * This is applicable to point-to-point links, not broadcast.
    * This involves a structured beam multiple wavelengths in diameter -- infeasibly large at 1-10 GHz frequencies.

    So what is it good for? Free-space optical comms! It could also be applied to sub-THz frequencies for increased range, but not to wavelengths as long as are commonly used today. Applications include backhaul for GSM towers and satellite-to-satellite comms.

    It's worth noting, however, that free-space optical comms are not particu

    • At those frequencies, wouldn't the doppler effect be more pronounced between two moving objects in space?

  • > 95.7 bits per hertz

    95.7 bits per cycles per second?

  • by Anonymous Coward

    Still trying to resolve whether OAM is more than pattern polarization in a regular antenna. If it is not, then:

    1) the spatial region of receiving the differently-polarized "streams" will spread out with distance from the transmitter, and

    2) there will be a finite isolation between the different polarization states in a real receiving device, essentially setting up a maximum signal to noise ratio (SNR); this sort of finite isolation between states is likely to exist in any event

    With any comms system, you can

    • by jo_ham (604554)

      1) it's not. This was discussed in the slashdot article that the summary briefly mentions involving a similar experiment done using radio waves instead of light. It is a technique that is additional to polarising the antenna.

      Polarisation is like, as the summary mentions, looking at the signal at different rotations on the axis - spin angular momentum. This adds the additional orbital angular momentum component (that axis orbiting something else in the case of the planet and sun analogy which is not perfect

  • Once they commercialize this, it will be found to cause cancerous-like growths in the brain and begin the zombie apocalypse!
  • by epine (68316) on Monday June 25, 2012 @11:38AM (#40439359)

    In short, this might just be exactly what our congested wireless spectrum needs.

    Good judgement comes from experience
    :: Experience comes from bad judgement
    :::: Abundance comes from alleviating congestion
    :: Congestion comes from delivering abundance.

    It's pretty much a theorem in transportation systems that you can't alleviate congestion by boosting capacity until the less direct or desirable routes are destitute.

    There should have been a Star Trek episode where high-end subspace polarizers keep disappearing from engineering consoles because the Ferengi have taken on a contract from Monster Cable to supply private Holodeck enthusiasts with the finest detail in nose hair.

  • http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6059486 [ieee.org] PDF for those with no IEEE access: http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120 [lub.lu.se] The short version: nothing new here and equivalence to traditional multiple-antenna methods, with same bandwidth limitations; move along.
    • by jmsp (1987118)
      Stop spamming please. You got your point, once is enough. Twenty times is spam.
  • I work in satellite communications, where circular polarization (e.g. LHCP and RHCP) is common, especially in some C-band links. Can someone explain to me how OAM is different from CP? Because it sure sounds like CP to me.

    And if they're modulating the data onto the phase, wouldn't that simply be phase shift keying?

    I read a short IEEE Spectrum article about this just yesterday, and I'm still puzzled. Tech writers tackling this subject would be well advised to mention CP in their writing and explain how th

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