back to article Want faster fibre? Get rid of the glass

One of the most irritating expressions people can use, “broadband at the speed of light”, is a little closer to coming true thanks to researchers from the University of Southampton, who have demonstrated air-filled fibres with propagation happening at 99.7 percent of c. In a conventional fibre, the glass acts as a waveguide: …


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  1. Eddy Ito

    Umm, minor point

    Light travels at the speed of light, full stop. It doesn't matter what material it travels in, it still travels at the speed of light and that speed may or may not be equal to the speed of light in a vacuum. Indeed light traveling in a Hoover still travels at the speed of light. Broadband on the other hand can travel no faster than the carrier frequency regardless of the speed of light, or the speed of any EM signal for that matter, in any particular medium.

    1. Robert E A Harvey

      Re: Umm, minor point

      Yes, true. But propagation factor is defined as the ratio to c, the speed of light in vacuo.

      PS: someone will now out-pedant both of us!

      1. Neoc

        Re: Umm, minor point

        Challenge accepted:

        c is used for the speed of waves in any material medium.

        c0 (that's c-subscript-0) is the speed of light in vacuum.

        1. Gavin King

          Re: Umm, minor point

          If I may "out-pedant" the pedant: as far as I can tell --- glancing through the four books at hand to check--- in all cases that I have used the speed of light "c" denotes the speed in a vacuum, whereas something else is used for the speed in a material.

          Some use " v " (which can be the phase velocity as well) some use " c' " and I'd usually use something along the lines of " c_{material} ".

          Not that I spend a lot of time doing this sort of stuff or anything!

      2. Whitter

        Re: Umm, minor point

        Indeed, but as a researcher pointed out only last week, (and on El Reg here: there really isn't any significant stretch of vacuum anywhere due to pesky background radiation particles being "in the background" as it were plus the even peskier virtual particles, with an extended field theory slapped on to fill the gaps.

    2. lambda_beta

      Re: Umm, minor point Hollow fibre propagates optics near speed of light

      Good points ... now is hollow fiber still fiber? (is it fibre?) Or do you mean a wave-guide?

      1. John Brown (no body) Silver badge

        Re: Umm, minor point Hollow fibre propagates optics near speed of light

        "now is hollow fiber still fiber?"

        I've got a duvet full of hollow fibre and not much light get through that!

        Mines the padded one.

      2. Euripides Pants

        Re: Umm, minor point Hollow fibre propagates optics near speed of light

        Hollow fiber is bamboo...

    3. Paul Kinsler

      Re: Light travels at the speed of light, full stop

      "speed of light" might mean one of two different things, depending on context. Either the fundamental speed limit as determined by relativity, which is the same as the speed of light in a classical vacuum. Alternatively, it might mean the spped that light gets from one end to the other of this stuff I have here (which will be less than the other definition).

      Here, the context given, i.e. "99.7% of the speed of light" strongly suggests that the first "relativistic speed limit" definition is the one meant.

      Lastly, most materials and waveguides have (both) temporal and spatial dispersion - their wave speeds vary with frequency (wavelength). This variation gives rise to a "group velocity", which is the speed a pulse will travel through, and this need not be especially similar to the (usually quoted) phase velocity. Generally, high-frequency (short wavelength) signals feel the medium/waveguide less; this has to be true in the very high frequency limit or something has gone wrong with causality. This high frequency behaviour means that you can get optical precursors that travel at near (vacuum) c even in a material, even if you send in an otherwise unremarkable pulse into a "slow" medium.

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  3. Rampant Spaniel

    This may be a silly question, but wouldn't they need to relay cables to take advantage of this? Thats a pretty expensive affair.

    1. gecho

      Or a very small tunnel boring machine.

  4. Anonymous Coward
    Anonymous Coward

    I smell a business opportunity!

    I smell a business opportunity! Look, the hyperfast stock traders are always looking for that edge - remember the story from a few weeks back about the guys who went from fiber to microwave link to shave a few microseconds off their ping to the stock exchange?

    So, now we have hollow fiber, running at .97c. How can we go faster? As somebody above suggested, we could go to a vacuum. I say take it one step better: By making the cavity smaller, you can exclude some of the possible modes of the quantum noise (see Casimir effect), and if quantum noise slows light down, then reducing it should allow the light to go faster, right? And that means faster times to the stock market, and that means MONEY MONEY MONEY BAYBEE! You *know* the stock market exploiters will be all over that!





    (now, all you good Reg readers who can see that the result of what I just described, even if you could actually realize it to practice, would be minuscule at best - do shut up, will you? I'm trying to get payback for my 401(k), OK?)

    1. JeffyPooh

      Re: I smell a business opportunity!

      Neutrinos straight through the Earth's crust/mantle/core. I suggested this last year when the boffins with the loose connector thought that they might have exceeded c. Same financial (il)logic.

    2. P. Lee

      Re: I smell a business opportunity!

      Why not go the whole hog with quantum entanglement?

      1. Robert Helpmann??

        Re: I smell a business opportunity!

        Why not go the whole hog with quantum entanglement?

        'Cause it won't work. Better check your coat's pockets for your quantum mobe; you might have lost it.

    3. mark 63 Silver badge
      Thumb Up

      Re: I smell a business opportunity!

      I wouldnt mind a miniscule share of the countless billions travelling through that place.

      either that or see them all first against the wall when the revolution comes.

    4. mIRCat

      Re: I smell a business opportunity!

      Why not make use of a time machine so your message is received before it is sent? People assume that time is a strict progression of cause to effect, but actually, from a non-linear non-subjective viewpoint, it's more like a big bowl of wibbly wobbly timey wimey... stuff.

      I'll take my coat, you know the one with the key.

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  5. Esskay

    Cue The Daily Telegraph headline:


    Back to reality though, what are the chances of this being mass produced at a decent price? Also the fragiliy of the fibres could be a factor... Sounds promising though, here's hoping something good comes of it.

  6. Adam 1


    " (ignoring router hops and regeneration)."

    For mine, these are the little details that shouldn't be ignored as they can be improved by way more than 30%.

  7. VeganVegan

    As the surfers say

    Totally tubular!

  8. simon 43

    patent pending

    If we're after propogation closer to the speed of light in a vacuum, why not evacuate these hollow fibres? ;-)

    Royalties via cheque or transfer, I'm not fussed.

    Cue someone who has the time to read the research to point out that's already factored in..... oh well, back to the time machine build!

  9. petur


    My ISP ( already sells me fibernet. Only a minor detail that they deliver it over the cable and that it barely gets plain ethernet speed (<100mbs). No idea what they would call normal fiber feeds, and most certainly not what they would call this. Probably faster than the speed of light.

  10. John Miles 1

    Attenuation killer in the small print

    Its a nice idea - but the closing paragraph says the attenuation is 3.5 dB/km. Current long-haul fibre has attenuation of 0.2 - 0.3 dB/km and one can go up to 100km before amplification. This new fibre would need an amplifier or regenerator every 10km, not very attractive! They need to fix the attenuation problem first.

  11. Tom 7

    water ingress

    its just bound to happen if there's a hole. Happens round here on cables without anywhere for the water to go.

  12. PJL500

    Nae shabby...

  13. 4ecks

    What's the tog rating?

    ←the winter one with the hollow fibre filling please.

  14. Anonymous Coward
    Anonymous Coward

    Been there, done that...

    Old news - reported by El Reg. There was another story on the reg, but I can't find it now.

  15. Andy 70

    pykies will still probably be ripping out the ground...

  16. Alan Brown Silver badge


    Propagation speed in waveguide is about 0.47 - perhaps not the best analogy to use :)

    1. Steven Jones

      Re: FWIW

      It's not an analogy. Fibre optic cables are dielectric waveguides. They are just as much waveguides as the microwave variety.

  17. Mike 16

    Yeah, what's with that loss figure?

    The loss does seem excessive. I recall several years ago some boffins at MIT did this sort of thing, just in time for the collapse of broadband market. So, since their main (achieved) goal was low loss (hence increased repeater spacing) they pivoted to selling the stuff for surgical laser guides. It seems folks get uncomfortable with the waste heat from conventional fiber delivering surgical power levels.

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