Boffins set networking record with marathon 12,000 km fiber data run A group of university researchers claim to have developed a method to increase the data bandwidth of fiber optic cables by eliminating a barrier that has limited the maximum power at which optical signals can be sent. The team from University of California, San Diego said its method of adjusting the frequency of light signals …
Dispersion sorted. Great.
What about loss? 12,000 km x 0.4 dB/km is 4800 dB.
Anyone else here understand dBs enough to laugh with me? I'm pretty sure that the ratio of 'The Big Bang' itself to a tiny Quantum of energy is significantly less than 4800 dB. Problem is my calculator isn't wide enough, by miles.
In lab experiments, the researchers at UC San Diego successfully deciphered information after it travelled a record-breaking 12,000 kilometers through fiber optic cables with standard amplifiers and no electronic regenerators.
Dude. No regenerators. Just amplifiers.
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"4800dB would possibly vaporize the planet..."
I dug out my 500 digit calculator.
4800 dB above a single quantum of energy would most assuredly vaporize the entire Universe a zillion zillion zillion... etc. ... times over. You'd only be safe if you hid behind some lossy cable.
Apparently they're using amplifiers, of the erbium doped variety?
I was trying to grasp the concept of 4800dB... and I found that the most stupid SPL competitor (sound pressure level) managed to put together a sound system capable of 170dB. For comparison, a noisy jet takes off at 130dB. And dynamite detonates with a 200dB "noise" shockwave.
After that, boffins measure in the Richter scale. Yes, the earthquake scale, which also happens to be logarithmic.
So yeah, 4800dB is one hell of a bang in terms of amplification. Well, at least the noise won't need expensive filtering gear anymore, (and amplification is still required), major achievement. Kudos.
"Learn the difference between logarithmic scales."
Except he did do the calculation correctly,
The whole point of using a logarithmic scale is so that you can do what he did. If each km causes a 0.4dB loss then 12000km will be 48000dB of loss. That's far too much and needs amplification.
"48000dB"
OMG.
If you understand dBs, then your fingers should have rebelled at even typing that in. The simple phrase "...thousand dB..." should cause a gut reaction like being punched.
As it was, I had to copy-and-paste your erroneous value with my eyes closed.
What you're referring to is Chromatic Disperation due to the fact that different wavelengths of light travel a slightly different speeds and yes, the effect can be compensated for by spools of negative dispersion fibre or, if using coherent modulation techniques, ignored completely.
But CD is a linear effect, it occurs regardless of what power level is launched into the fibre. The Kerr effect, along with other effects such as Raman Scattering, Stimulated Brillouin Scattering, Phase Mixing, and probably a number of other effects, are what are referred to as non-linear effects and become worse as the launch power increases - you can even get a situation where the optical power can loosen the bonds between the glass molecules and allow acoustic noise (eg., the vibrations from passing traffic) to be coupled into the optical signal.
The Kerr effect is just one of a number of non-linear effects that need to be overcome.
"The Kerr effect, along with other effects such as Raman Scattering, Stimulated Brillouin Scattering, Phase Mixing, and probably a number of other effects, are what are referred to as non-linear effects and become worse as the launch power increases"
I do understand that, but I thought this would only be relevant in dispersion-less fibres as with dispersion the wave-front constantly changes, thus averaging out all non-linear effects.
I'd put an e-beer up as a bet that they didn't actually have 12,000 km of fiber.
I'd bet that they simulated it, and neglected the small matter of the approximately 4800 dB of loss.
Even if they had erbium doped optical amplifiers, then how did they pre-charge the doped sections with the other erbium pumping laser? Even from both ends, it's still 2400 dB (is 10^240) for the erbium pumping laser.
Inquiring minds want to know. Is this yet another university BS press release? They're so common these days.
edit. Or are they using the HV DC powered electronic amplifiers? Are they practical over this distance? Industry was trying to get away from them.
Yup - I was wondering that. 7,456 miles of production cable wound around the lab or even the whole campus sounds somewhat impactical. And possibly slightly expensive.
So, unless it was a bank of reels of the fibre equivalent of 44 swg copper wire I wonder how they got their results. We need to see this repeated in a real life installation somewhere - not necessarily 7,456 miles but long enough to prove the concept.
It also raises a somewhat off topic question in my mind. I know very little about fibre optic cables. I gather they are a plastics material. I'm wondering how long they last - and does the light causes degradation (eg yellowing or an increase in opacity of the fibre)? If this can / does happen will increasing optical power significantly shorten the effective life of the cable?
Fibres are extremely thin, so you can easily have that amount on simple spools. In the OTDR experiment we had at university we had several kilometres of fibre in a rather small case. So we are talking about a room or so, certainly not portable, but you can easily find some space for it in your lab.
"several" km .NE. "12,000" km
The actual cables to cross an ocean tend to completely fill-up a large ship.
We've established that they'd have to be using HV DC powered amplifiers, because the erbium doped versions would be out of reach of their pumping lasers due to the same loss issue. HV DC powered amplifiers require a fairly thick cable to carry the HV DC.
12,000 km is 12,000,000 m. TWELVE MILLION METERS of thick cable.
If they just installed the amplifiers between the reels of thin fiber, and then fed them with HV DC using short cables, then they're cheating w.r.t. the "12,000 km: claim.
THEREFORE - I call BS on this.
They seem to have done two experiments. One over a 1.1 km fibre and a second over 85 km, which according to Christian Berger above is a feasible amount for a lab. Zero mentions of simulations in the paper.
To quote (hope this is OK by El Reg?):
The first experiment illustrates Kerr-inversion physics and nonlinear reversal in a pump-probe configuration in the absence of noise. Both the intense (pump) and weak (probe) waves had a high signal-to-noise ratio (SNR) and propagated over a short, nearly lossless, highly nonlinear fiber (HNLF) segment to guarantee that Kerr-induced impairment would dominate over stochastic, noise-induced distortion. Pump and probe waves, separated by 30 nm, were derived from the parametric comb source and had SNR of more than 40 dB. The pump and probe were launched into a HNLF 1100 m in length, with nonlinear parameter of 7 W−1 km−1, dispersive parameters β2 = 37.9 ps2/km and β3 = –0.06 ps3/km, and transmission loss α = 0.6 dB/km. This segment was specifically selected to guarantee a sufficient walk-off between the pump and probe and to provide a clear distinction among the nonlinear interaction mechanisms.
In the second experiment, we demonstrated the reversal of nonlinear distortion in a three-channel coherent wavelength division multiplex (WDM) transmission. In this case, the NLC is performed in a loop (26) emulating a modern communication link: Signal is sent over a total distance of 1020 km and re-amplified periodically after each span of 85 km of the standard single-mode fiber, as shown in Fig. 3.
This is not my field at all but hopefully satisfies some inquiring minds.
How have they cheated - the standard supply voltage to an in-line amplifier (ILA) is 50 volts, the only reason high voltage is used in submarine cables is because the ILAs are connected in series on the power conductor.
Our office lab has quite a few spools of fibre mounted up in the ceiling space, a mixture of 50, 100 and 200km spools - they are not very big, about 2/3rds the size of a box of cat5. The size difference between a production cable can be handled, laid on the ocean floor up to 10km down, left there to work for 20 years or more, and a spool of fibre designed to be installed in a lab is, strangely enough, hugely different. The naked fibre wound on to a lab spool is thin, so thin it can be hard to see when looking at a single strand. You could, literally, fit millions of km of naked fibre into a single cable tank on a ship.
Building up a set of spools to 12,000km is going to cost a bit, will weigh a lot and will take up a good sized corner of your office, but if you have the budget it's a trivial thing to do. How the DC power gets to any ILAs is irrelevant - you design the production cable insulation to meet the power feed voltage needed for the span at 50 volts/ILA, but that has nothing to do with its optical characteristics.
It's normal practice when testing a system in the factory to rack up the ILAs and terminals side by side and interconnect them with spools connected in series to provide however many km of fibre each span is designed for - no cheating and a lot more convenient than having a factory hundreds of km long and spending half the day driving between racks. (I've spent more than enough time driving up and down a system, taking two weeks to resolve a supervisory channel problem that could have been sorted in the factory in a day or so with everything side by side).
THEREFORE - based on many years of working with long haul high capacity fibre systems and quite a few years of working for a manufacturer of both terrestrial and submarine systems (including time at the factory observing pre-delivery tests on behalf of a customer), I'm going to call no BS on this one.
"They did it by using the frequency comb to synchronize the frequencies of the various channels of optical information traveling across a given fiber. Ordinarily, such signals are subject to crosstalk caused by a physical phenomenon known as the Kerr effect. The longer the fiber and the higher the power level, the greater the crosstalk."
Seeing as the this is about Wide Area Networking, are we talking about the WAN-Kerr effect?
Ok, yes, coat, got it, bye
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