4 ms·

I wonder how long it will be before we see the first hollow-core fiber subsea cables. They are 50% faster, and tests from the last year or two have seen record

I wonder how long it will be before we see the first hollow-core fiber subsea cables. They are 50% faster, and tests from the last year or two have seen record low signal losses. https://www.laserfocusworld.com/fiber-optics/article/14196057/hollowcore-fiber-is-now-clearer-than-glass https://www.laserfocusworld.com/fiber-optics/article/1419605... https://www.ofsoptics.com/wp-content/uploads/Hollow-Core-Fiber-Cable-FINAL.pdf https://www.ofsoptics.com/wp-content/uploads/Hollow-Core-Fib...

happyopossum 4y ago
> They are 50% faster No, pretty sure light still travels through them at C. What they can do is carry more data, largely by having lower error rates.
- theideaofcoffee 4y ago
  'c' is dependent on the medium. The value of c as it is commonly known, 300 million meters per second, is in vacuum. Light traveling through other media is affected by its index of refraction, in the case of silica fiber, that is approximately 1.5 so radiation propagates much slower through silica than it does a vacuum. Since gases have low refractive indicies already, within a hundred ppm or so of a vacuum, you could essentially round air to 1.
  - ortusdux 4y ago
    I've heard that high frequency traders are interested in Starlink's planned laser links because they could open up routes that are faster than traditional terrestrial fiber.
    - guipsp 4y ago
      I think that if you are a HFT, you probably have a server set up next door.
      - samwillis 4y ago
        The suggestion is about trading across multiple exchanges, for example between London and NY. Going via Starlink is potentially quicker than a fiber under the Atlantic. They will have servers “next door” to the exchanges, but need the servers to have incredible low latency connections to each other.
    - theideaofcoffee 4y ago
      Yeah, that would make sense. There are links that have been built by various HFT firms and banks [0] [1] that use microwaves instead of fiber buried in the ground simply because of this speed-of-light-in-media limitation. They can shave a few hundred nanoseconds (or something, I don't want to do the math right now) because of a higher signal propagation speed and get a trade in faster than their competitors. Same thing with a laser link like this. Edit: cf. [0] https://arstechnica.com/information-technology/2016/11/private-microwave-networks-financial-hft/ https://arstechnica.com/information-technology/2016/11/priva... [1] https://www.reuters.com/article/us-highfrequency-microwave/lasers-microwave-deployed-in-high-speed-trading-arms-race-idUSBRE9400L920130501 https://www.reuters.com/article/us-highfrequency-microwave/l...
    - cycomanic 4y ago
      I know the main people behind much of the hollow core work being done. Much of their financing is coming from HFT related firms.
- maxfan8 4y ago
  Light only travels at C in a vacuum (so it doesn't actually travel at C in a standard fiber optic cable, it's actually much slower).
- scottlamb 4y ago
  "c" is the speed of light in a vacuum. Traditional fiber optic cables are very much not a vacuum, with an index of refraction of ~1.5, so light travels through them at ~2/3c. In contrast, light actually travels at nearly c through hollow core cables.
- deleted 4y ago
  [deleted]
- idiotsecant 4y ago
  It's so nice when someone other than myself is confidently incorrect.
controversial97 4y ago
I might be totally wrong; It seems likely to me that, due to capillary action, if a hollow undersea fiber gets physically cut then seawater would flow into the hollow center. The ends of the fiber might be at different depths with a pressure difference that could move water a long way into the fiber. I imagine the length that water got into would be ruined even if the water was pushed out again. I conjecture that undersea hollow-core might end up being expensive to maintain.
- LargoLasskhyfv 4y ago
  I may be even more wrong, but maybe this leads to a more modular way of building/laying these "cables". I imagine that you need less of them, because "faster" also means longer range until attenuation kicks in. How much more range/less amplifiers compared to current state of the art I don't know. I'd think it should be possible to lay down a new part the whole length between two amplifiers/laser pumps/couplings/ and "plug" it in by remote controlled submersibles, instead of lifting up the broken ends, and "splicing" it on the ship. Like pre-made Cat-5/7 with RJ-45 plugs, so to speak :-)
- deleted 4y ago
  [deleted]
- esoterae 4y ago
  IIRC individual fibers are terminated every Nkm at a repeater. Not that it wouldn't be spendy, but I would also conjecture replacing a segment of fixed length instead of just gluing the ends back together might still be a reasonably strong constraint on unplanned repair cost (and also probably providing a pretty strong lower constraint as well--notably higher than solid core).
  - xhrpost 4y ago
    I don't think they are terminated every Nkm anymore. We have been able for quite some time to re-energize the signal directly in the optical core without needing to convert it to electric then back. https://en.wikipedia.org/wiki/Laser_pumping https://en.wikipedia.org/wiki/Laser_pumping
geph2021 4y ago
With hallow-core, Spread Networks[1] could be back on top again! 1 - https://en.wikipedia.org/wiki/Spread_Networks https://en.wikipedia.org/wiki/Spread_Networks
maxwindiff 4y ago
The "50% faster" stat is talking about latency, which is not really what subsea cables are about (massive bandwidth). The more important figure is the attenuation at frequency bands used in telecommunication (C-band and L-band). According to the article, hollow core fibers are still much worse than solid core fibers (0.28 dB/km vs 0.14 dB/km).

happyopossum 4y ago

> They are 50% faster No, pretty sure light still travels through them at C. What they can do is carry more data, largely by having lower error rates.

theideaofcoffee 4y ago
'c' is dependent on the medium. The value of c as it is commonly known, 300 million meters per second, is in vacuum. Light traveling through other media is affected by its index of refraction, in the case of silica fiber, that is approximately 1.5 so radiation propagates much slower through silica than it does a vacuum. Since gases have low refractive indicies already, within a hundred ppm or so of a vacuum, you could essentially round air to 1.
- ortusdux 4y ago
  I've heard that high frequency traders are interested in Starlink's planned laser links because they could open up routes that are faster than traditional terrestrial fiber.
  - guipsp 4y ago
    I think that if you are a HFT, you probably have a server set up next door.
    - samwillis 4y ago
      The suggestion is about trading across multiple exchanges, for example between London and NY. Going via Starlink is potentially quicker than a fiber under the Atlantic. They will have servers “next door” to the exchanges, but need the servers to have incredible low latency connections to each other.
  - theideaofcoffee 4y ago
    Yeah, that would make sense. There are links that have been built by various HFT firms and banks [0] [1] that use microwaves instead of fiber buried in the ground simply because of this speed-of-light-in-media limitation. They can shave a few hundred nanoseconds (or something, I don't want to do the math right now) because of a higher signal propagation speed and get a trade in faster than their competitors. Same thing with a laser link like this. Edit: cf. [0] https://arstechnica.com/information-technology/2016/11/private-microwave-networks-financial-hft/ https://arstechnica.com/information-technology/2016/11/priva... [1] https://www.reuters.com/article/us-highfrequency-microwave/lasers-microwave-deployed-in-high-speed-trading-arms-race-idUSBRE9400L920130501 https://www.reuters.com/article/us-highfrequency-microwave/l...
  - cycomanic 4y ago
    I know the main people behind much of the hollow core work being done. Much of their financing is coming from HFT related firms.
maxfan8 4y ago
Light only travels at C in a vacuum (so it doesn't actually travel at C in a standard fiber optic cable, it's actually much slower).
scottlamb 4y ago
"c" is the speed of light in a vacuum. Traditional fiber optic cables are very much not a vacuum, with an index of refraction of ~1.5, so light travels through them at ~2/3c. In contrast, light actually travels at nearly c through hollow core cables.
deleted 4y ago
[deleted]
idiotsecant 4y ago
It's so nice when someone other than myself is confidently incorrect.

controversial97 4y ago

I might be totally wrong; It seems likely to me that, due to capillary action, if a hollow undersea fiber gets physically cut then seawater would flow into the hollow center. The ends of the fiber might be at different depths with a pressure difference that could move water a long way into the fiber. I imagine the length that water got into would be ruined even if the water was pushed out again. I conjecture that undersea hollow-core might end up being expensive to maintain.

LargoLasskhyfv 4y ago
I may be even more wrong, but maybe this leads to a more modular way of building/laying these "cables". I imagine that you need less of them, because "faster" also means longer range until attenuation kicks in. How much more range/less amplifiers compared to current state of the art I don't know. I'd think it should be possible to lay down a new part the whole length between two amplifiers/laser pumps/couplings/ and "plug" it in by remote controlled submersibles, instead of lifting up the broken ends, and "splicing" it on the ship. Like pre-made Cat-5/7 with RJ-45 plugs, so to speak :-)
deleted 4y ago
[deleted]
esoterae 4y ago
IIRC individual fibers are terminated every Nkm at a repeater. Not that it wouldn't be spendy, but I would also conjecture replacing a segment of fixed length instead of just gluing the ends back together might still be a reasonably strong constraint on unplanned repair cost (and also probably providing a pretty strong lower constraint as well--notably higher than solid core).
- xhrpost 4y ago
  I don't think they are terminated every Nkm anymore. We have been able for quite some time to re-energize the signal directly in the optical core without needing to convert it to electric then back. https://en.wikipedia.org/wiki/Laser_pumping https://en.wikipedia.org/wiki/Laser_pumping

geph2021 4y ago

With hallow-core, Spread Networks[1] could be back on top again! 1 - https://en.wikipedia.org/wiki/Spread_Networks https://en.wikipedia.org/wiki/Spread_Networks

maxwindiff 4y ago

The "50% faster" stat is talking about latency, which is not really what subsea cables are about (massive bandwidth). The more important figure is the attenuation at frequency bands used in telecommunication (C-band and L-band). According to the article, hollow core fibers are still much worse than solid core fibers (0.28 dB/km vs 0.14 dB/km).