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Networking Communications Network Upgrades

Scientists Overcome One of the Biggest Limits In Fiber Optic Networks 62

Mark.JUK writes: Researchers at the University of California in San Diego have demonstrated a way of boosting transmissions over long distance fiber optic cables and removing crosstalk interference, which would mean no more need for expensive electronic regenerators (repeaters) to keep the signal stable. The result could be faster and cheaper networks, especially on long-distance international subsea cables. The feat was achieved by employing a frequency comb, which acts a bit like a concert conductor; the person responsible for tuning multiple instruments in an orchestra to the same pitch at the beginning of a concert. The comb was used to synchronize the frequency variations of the different streams of optical information (optical carriers) and thus compensate in advance for the crosstalk interference, which could also then be removed.

As a result the team were able to boost the power of their transmission some 20 fold and push data over a "record-breaking" 12,000km (7,400 miles) long fiber optic cable. The data was still intact at the other end and all of this was achieved without using repeaters and by only needing standard amplifiers.
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Scientists Overcome One of the Biggest Limits In Fiber Optic Networks

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  • by Anonymous Coward on Sunday June 28, 2015 @11:49AM (#50006651)

    Conductor keeps them on the same rhythm. Concert master/mistress is the person in charge of getting everyone in tune.

    • by Anonymous Coward

      I always thought that the conductor is essential during rehearsals, but little more than showmanship during actual performances. After all, when Maurice Ravel, who was a rather poor conductor, was forced to conduct, he instructed the players to play as they would usually do, and he would just strive to keep up with them.

    • Well, to be more specific the conductor facilitates a single interpretation in the change of pulse and other variables open to interpretation. A good orchestra can easily keep a steady pulse and play together rhythmically without a conductor just fine. They can even start together blindfolded, this is about listening to each other, esp breathing, it is actually not as hard as you might think. A very good orchestra can even come to a good consensus as to musical interpretation without a conductor, but will

    • Perhaps he was thinking of a lightening conductor
  • I thought the conductor just waved a baton in some strange patterns and got paid handsomely for that. He is so ashamed for getting paid so much for doing so little he does not dare show his face to the audience, and turns his back to them. Never knew it was his job to tune all the instruments of the entire orchestra before the concert.
    • by whodat54321 ( 3823985 ) on Sunday June 28, 2015 @12:13PM (#50006773)
      Actually, perhaps the article should perhaps correctly use the term 'concertmaster' (in orchestras, usually the first violin player), who also synchronizes the bow movements of the bowed instruments in the orchestra. Scanning the article linked, it seems most of what USCD is trying is a digital version of what is known in the analog world (particularly FM radio) as pre-emphasis. This principle has been known in the analog world for about 80 years, so it's kind of a shock that these techniques are not better known in the digital world. I think that this is actually perhaps a form of laziness, given the very high bandwidth and signal to noise ratios possible with digital that are not as much of an issue until very long distances are involved. I don't use that term loosely, as I've held an FCC commercial license for over 30 years, so basic engineering stuff like this coming out of a lab is a bit shocking. Perhaps a bit of old school techniques need to be applied to modern communications to get more out of them.
      • by Anonymous Coward

        Perhaps a bit of old school techniques need to be applied to modern communications to get more out of them.

        I suspect that the problem isn't lack of knowledge of the subject but rather that the 80 years old principle is a bit more problematic to apply to optics than just knowing the theory.

        • Maybe, but I suspect maybe not. The electromagnetic spectrum (which includes light frequencies) has particular characteristics that do not change much with increases in frequencies, closed system or not. I seem to remember the original 'Red Book' standard for CDs (when 14 bit audio was used in early pressings) that required a bit of eq due to quantization distortion (similar to the LP record) to compensate for the bandwidth restrictions until 16 bit audio came along. Shift that distortion and signal/nois
          • by Anonymous Coward

            No, this is much more about co-channel interference between frequencies (colors). Coming from the RF world, imagine a non-linear filter that ends up looking like a comb on a spectrum analyzer, filtering the guard bands so as to reduce adjacent-channel interference.

          • by Anonymous Coward

            The electromagnetic spectrum (which includes light frequencies) has particular characteristics that do not change much with increases in frequencies, closed system or not.

            Which is why you can take the same circuit that a grade school kid can build to make an FM radio and get frequency modulation at optical frequencies? Oh wait, it isn't that straightforward. Frequency shifting and nonlinear effects change drastically in different regimes, as does interaction of EM waves and matter. What you can do with circuits and traces at low frequency RF becomes different when you start needing waveguides, or get into non-linear fiber behavior that starts to introduce atomic physics e

          • Maybe, but I suspect maybe not. The electromagnetic spectrum (which includes light frequencies) has particular characteristics that do not change much with increases in frequencies, closed system or not.

            Granted, but optical signals are not generated by a coil of wire and interleaved metal plates. You can't just tweak a capacitor to adjust the frequency of a laser.

  • So the problem is cross contamination between fiber channels due to frequency differentials, I think they equalized all frequencies somehow but I don't fully get it. Red is longer than blue for example and if separate strands of fiber carry different 'colour' and frequencies 'bleed' from strand to strand how do you equalize that exactly? Have wave peaks correspond? How? Are they proportionate to remain synchronized? If this is a serious problem, why not add more isolation between strands?

    • by Anonymous Coward

      I think the problem is with multiple frequencies in the same fiber, not color bleeding between adjacent physical fibers.
      But the article isn't very helpful at making any of this clear.

    • It is interference caused by reflections off the ends of the fiber. Each fiber carries multiple colors (as the AC says above), which all reflect different amounts off the ends. Blocking these reflections is likely harder than RF as RF is all electrical in nature, light is harder.

  • Since the diameter of the earth is 7 926.3352 miles, this could conceivably remove any need for repeaters. I still bet it will not improve fiber rollout by big telcos in the U.S.

    • Since the diameter of the earth is 7 926.3352 miles, this could conceivably remove any need for repeaters.

      I got the impression from the (sketchy) article that repeater AMPLIFIERS were still needed but repeater REGENERATORS were not.

      I.e. you still needed to boost the strength of the signal to make up for the losses. But the progressive degradation of the quality of the signal - with data from different frequency bands bleeding into other bands (especially in the amplifiers themselves) due to nonlinear "mixi

      • I got the impression from the (sketchy) article that repeater AMPLIFIERS were still needed but repeater REGENERATORS were not.

        Then again - another part of the article makes it look like an additional result was that they could boost this less-subject-to-degradation-by-nonlinear-distortions signal at the start until the fibre itself was acting non-linearly, in order to get a signal strong enough to survive a much longer hop.

        So it's not clear to me whether the distance was achieved by:
        - long hops enab

      • Since the diameter of the earth is 7 926.3352 miles, this could conceivably remove any need for repeaters.

        true, although I'm not sure if "through the center of the earth" is the next big thing for high speed communications.

        • by mysidia ( 191772 )

          although I'm not sure if "through the center of the earth" is the next big thing for high speed communications.

          It won't be until we develop technology that can shoot neutrinos through earth, capture them on the other side, and demodulate the encoded message.

        • Just comparing for scale, others did it better than me below.

  • by Anonymous Coward

    Literally, an autoplaying Dove shampoo commercial on Slashdot. Starts playing 10 minutes after the site loads when the tab has even been in focus for about that time. Fucking pathetic times for this website

  • Link to actual paper (Score:4, Informative)

    by PaperGeek ( 1045780 ) on Sunday June 28, 2015 @12:38PM (#50006895) Homepage
    Interesting article but very light on details. I would love to read the actual paper but looks like it was published in Science. The actual press release here: http://ucsdnews.ucsd.edu/press... [ucsd.edu] has slightly more info than the linked article. This link to the PDF from August 2014 with the theoretical basis is free: http://ieeexplore.ieee.org/sta... [ieee.org] It looks like they are boosting WDM signals so this would work with existing long-range infrastructure.
  • Scale (Score:5, Informative)

    by denbesten ( 63853 ) on Sunday June 28, 2015 @01:01PM (#50007001)

    To help understand the scale, the cable length is approximately the diameter of the earth (12742 km).

    It is also 25-50% longer than the undersea hop for the longest cable paths (NY to London, LA to Sydney, San Francisco to Tokyo, Sao Palo to Gibraltar, etc.). This has the potential to allow electronics to stay on land, where they are easily maintainable and upgradable and with easy access to electricity.

    Interesting development, indeed.

    • Re:Scale (Score:4, Interesting)

      by PaperGeek ( 1045780 ) on Sunday June 28, 2015 @01:19PM (#50007081) Homepage
      More important than distance is the amount of dB loss they are able to overcome. Any L1 photonic switching device will introduce a certain amount of insertion loss which equates to length (connectors, mirrors, mirrors, connectors). Being able to tolerate additional insertion loss doesn't just mean more length, it means you can introduce more layers of all-optical switching. Even using a single all-optical switch might introduce 2-2.5dB of insertion loss. If you increase the haul length you are opening the door for more all-optical switching. The amount of silicon-based processing to convert optical to electrical and back again (typical repeater) gets very expensive when you are talking about terabytes of data.
    • by r0kk3rz ( 825106 )

      To help understand the scale, the cable length is approximately the diameter of the earth (12742 km).

      Spanning the diameter is cool and all but perhaps not the most useful comparison until we start laying cables through the core of the planet.

      Perhaps a more useful comparison is to the circumference (40,075 km), so slightly over a quarter of the way around the planets surface.

  • My understanding that the transmissions over modern fibers use all sorts of tricks to pack more information into it, including frequency modulation [wikipedia.org], multiple polarization states [wikipedia.org], etc. I wonder how this new frequency comb technique plays with those.

    • Reading their theoretical paper, it looks like they used the typical compression technologies used nowadays: QAM (quadrature amplitude modulation) and WDM (wave division multiplexing). http://ieeexplore.ieee.org/sta... [ieee.org] Definitely an interesting development.
  • Crosstalk? It's optical. make the casing out of an opaque material. I didn't think EM radiation and radio waves, etc can create new photons inside of a plastic material. What crosstalk are they talking about?
  • Kerr effect (Score:4, Interesting)

    by rfengr ( 910026 ) on Sunday June 28, 2015 @02:23PM (#50007307)
    I guess no one bothered to RTFA and delve deeper. Looks like the Kerr effect is the non-linearity of the refractive index; i.e. the refractive index changes with power, so that limits the light intensity they can shoot down the fiber. Looks like this development is a form of predistortion, most likely to aligning the phase of the carriers/channels to limit the crest factor (instantaneous total amplitude of combined channels) to minimize the kerr effect. We do this in the RF comms industry, but doing it optically is probably very tricky.
  • by Anonymous Coward on Sunday June 28, 2015 @02:32PM (#50007349)

    From PBUK at ISPreview -

    "The team have done an impressive experiment, but their press office could do with some wide reading.

    Pre-distortion of signals is already used in the fibre systems deployed by BT, Virgin Media, Vodafone, O2, SSE, and many others. The same coherent technology is already doing 22,000km unrepeatered across the Pacific. A 20 fold launch power improvement is only 13dB, which is about 50km.

    What is new is processing all the channels together to calculate the pre-distortion. Lovely idea for the lab, but wouldn’t work in practice where channels are deployed one at a time, as each transmitter costs as much as a house (so you don’t deploy them unless you use them)."

  • by kramer2718 ( 598033 ) on Sunday June 28, 2015 @03:29PM (#50007589) Homepage

    Because of the monopolistic stranglehold that companies such as Comcast and Verizon hold over the last mile, American consumers won't see a dime of any cost savings from this.

    Meanwhile consumers in Europe and Asia will continue to see faster cheaper broadband.

  • No information on bandwidth, signal strength, channel separation or anything else. Only that it "acts like a concert conductor".
    How low can a scientific article sink, and still be the basis for a slashdot story? This must be a new low.

    Current trans oceanic fibers do transmit multiple colors at high speed with amplifiers on the seabed and no regenerators. New installations carry 64 Tb/s per fiber. and often 64 fibers are laid. Some are left dark, but theoretical capacity for a cable is therefore 8192 TB/s bi

  • I thought dispersion was a greater problem than cross-talk.
  • I assume less electronics in-cable would result in more harbor 'accidents' for the NSA repair crews to 'fix'.

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