4 ms·

> I wonder how much data per unit of time this is capable of transporting. The max throughput of fiber optic cables isn't exactly constant. As fiber optic mode

by varenc 2y ago

> I wonder how much data per unit of time this is capable of transporting. The max throughput of fiber optic cables isn't exactly constant. As fiber optic modem and DSP technology improves you can get much higher speeds on 15+ year-old cables than were ever possible when they were laid. Recently I saw an article about researchers getting 300,000 Gbit/s over existing fiber optic cables (though I'm sure that's a long way from being a deployable technology): https://www.aston.ac.uk/latest-news/aston-university-researchers-send-data-45-million-times-faster-average-broadband https://www.aston.ac.uk/latest-news/aston-university-researc...

SAI_Peregrinus 2y ago
This applies to single-mode cables, but much less to multi-mode cables. Of course long-distance cable like this is always single-mode, but it's worth keeping in mind if building a fiber network inside a building.
- a20eac1d 2y ago
  Can you use single mode fiber in a house, or do the transceiver only work over much longer distances? Is transceiver burn out an issue?
  - jtriangle 2y ago
    You can use SM for short runs, you just have to match the optics to the cable/distance you're looking to use. Tons of very fast single mode optics out there that only expect <300m runs. That said, it's likely not worth it, given that cabling is typically viewed as a ~10 year investment, and if you're installing OM4 Multimode fiber in a house you're not likely to hit the limit of that fiber within 10 years even in extreme use cases.
    - a20eac1d 2y ago
      But why stop at 10 years? If the theoretical bandwidth limit of SM Fiber is above 100 Gbit/s then there is simply no way that a household will need more internal bandwidth than that. Even for the next 20-30 years, because other technologies (like SATA) will be the limiting factor. I believe this could be a case of future proofing that will actually last 30-40 years, no?
      - jtriangle 2y ago
        10 years is the guideline because you can't predict most of the future, but, you can predict the physical wear fairly well. It's likely that the plastic terminations will be iffy by that point basically, which means reterminating, or, running new fiber, and most of the time you'll just run new fiber.
colmmacc 2y ago
The Shannon limit is constant if you assume reasonable but idealized SNR values for the medium, and gives you a real "law of physics" upper limit ... typically still many orders of magnitude beyond what we can transmit today. But it's amazing how effective DSP can be; trellis coding managed to get modems to squeeze right up to the Shannon limit of POTS telephone connections.
- SideQuark 2y ago
  > The Shannon limit is constant if you assume reasonable but idealized SNR values for the medium The Shannon limit is changed by changing technology over the medium, not the other way around. If you signal with light on/off pulses, you get one limit. If you add polarization tricks (using different physical properties and tech), you get another limit. As you add QAM and a zillion other tricks, you get another channel limit. If you add quantum superdense coding, you get another channel limit. Each of those, until we learned there is yet another layer of physics and tech, would be "the Shannon Limit." All of these can be done on the same medium. The Shannon limit is a mathematical *model* of a channel. It's not a physical/technological limit. Here [1], for example, is a paper pointing this out for transoceanic undersea optical cables. "As pointed out in Section 9.3, the Shannon limit is only limiting if we assume there is no technical way to further improve the QoT..." Technology changes routinely change the "Shannon Limit," since that limit has almost nothing to do with physics. Physics and the signaling technology define a Shannon Limit for that particular channel combination, nothing more. [1] https://www.sciencedirect.com/topics/engineering/shannon-limit https://www.sciencedirect.com/topics/engineering/shannon-lim...
  - immibis 2y ago
    There is also a technology-independent Shannon limit for a cable. You can calculate Shannon limits based on the bandwidth and noise of your specific fiber-optic transceivers, which can improve, but you can also calculate one based on the cable itself. The Shannon limit already accounts for any number of channels and any level of QAM.
    - 2y ago
tjoff 2y ago
Though surely the repeaters in a cable, such as the one in the article, presents hard limits?
- markonen 2y ago
  They’re probably amplifiers rather than repeaters. Optical amplifiers don’t need to decode the signal to work. Here’s Wikipedia on erbium-doped fiber amplifiers: > A relatively high-powered beam of light is mixed with the input signal using a wavelength selective coupler (WSC). The input signal and the excitation light must be at significantly different wavelengths. The mixed light is guided into a section of fiber with erbium ions included in the core. This high-powered light beam excites the erbium ions to their higher-energy state. When the photons belonging to the signal at a different wavelength from the pump light meet the excited erbium ions, the erbium ions give up some of their energy to the signal and return to their lower-energy state. https://en.wikipedia.org/wiki/Optical_amplifier https://en.wikipedia.org/wiki/Optical_amplifier
- wiml 2y ago
  I think they're mostly laser amplifiers these days. So they're agnostic to modulation or WDM. But I assume there's still a noise/gain tradeoff.
ductsurprise 2y ago
Reminds me of the early dialup to DSL communication over standard telephone lines evolution.
nradov 2y ago
You're referring to single continuous fiber optic cables on land. Long undersea cables incorporate powered repeaters. Those can't be upgraded in situ with improved technology.
- doikor 2y ago
  They can just not really worth the hassle/money. You can pull the cable up and change them out if you want. Pulling a cable up, cutting a damaged part out of it and putting a new piece in is done all the time to fix damaged cables.
- Suppafly 2y ago
  would the repeaters need to be replaced? if you are compressing the data differently or sending it faster or whatever, I'm not sure the repeaters care, they are just amplifying the signal, not decoding it and resending it.

by varenc 2y ago

SAI_Peregrinus 2y ago

This applies to single-mode cables, but much less to multi-mode cables. Of course long-distance cable like this is always single-mode, but it's worth keeping in mind if building a fiber network inside a building.

a20eac1d 2y ago
Can you use single mode fiber in a house, or do the transceiver only work over much longer distances? Is transceiver burn out an issue?
- jtriangle 2y ago
  You can use SM for short runs, you just have to match the optics to the cable/distance you're looking to use. Tons of very fast single mode optics out there that only expect <300m runs. That said, it's likely not worth it, given that cabling is typically viewed as a ~10 year investment, and if you're installing OM4 Multimode fiber in a house you're not likely to hit the limit of that fiber within 10 years even in extreme use cases.
  - a20eac1d 2y ago
    But why stop at 10 years? If the theoretical bandwidth limit of SM Fiber is above 100 Gbit/s then there is simply no way that a household will need more internal bandwidth than that. Even for the next 20-30 years, because other technologies (like SATA) will be the limiting factor. I believe this could be a case of future proofing that will actually last 30-40 years, no?
    - jtriangle 2y ago
      10 years is the guideline because you can't predict most of the future, but, you can predict the physical wear fairly well. It's likely that the plastic terminations will be iffy by that point basically, which means reterminating, or, running new fiber, and most of the time you'll just run new fiber.

colmmacc 2y ago

The Shannon limit is constant if you assume reasonable but idealized SNR values for the medium, and gives you a real "law of physics" upper limit ... typically still many orders of magnitude beyond what we can transmit today. But it's amazing how effective DSP can be; trellis coding managed to get modems to squeeze right up to the Shannon limit of POTS telephone connections.

SideQuark 2y ago
> The Shannon limit is constant if you assume reasonable but idealized SNR values for the medium The Shannon limit is changed by changing technology over the medium, not the other way around. If you signal with light on/off pulses, you get one limit. If you add polarization tricks (using different physical properties and tech), you get another limit. As you add QAM and a zillion other tricks, you get another channel limit. If you add quantum superdense coding, you get another channel limit. Each of those, until we learned there is yet another layer of physics and tech, would be "the Shannon Limit." All of these can be done on the same medium. The Shannon limit is a mathematical *model* of a channel. It's not a physical/technological limit. Here [1], for example, is a paper pointing this out for transoceanic undersea optical cables. "As pointed out in Section 9.3, the Shannon limit is only limiting if we assume there is no technical way to further improve the QoT..." Technology changes routinely change the "Shannon Limit," since that limit has almost nothing to do with physics. Physics and the signaling technology define a Shannon Limit for that particular channel combination, nothing more. [1] https://www.sciencedirect.com/topics/engineering/shannon-limit https://www.sciencedirect.com/topics/engineering/shannon-lim...
- immibis 2y ago
  There is also a technology-independent Shannon limit for a cable. You can calculate Shannon limits based on the bandwidth and noise of your specific fiber-optic transceivers, which can improve, but you can also calculate one based on the cable itself. The Shannon limit already accounts for any number of channels and any level of QAM.
  - 2y ago

tjoff 2y ago

Though surely the repeaters in a cable, such as the one in the article, presents hard limits?

markonen 2y ago
They’re probably amplifiers rather than repeaters. Optical amplifiers don’t need to decode the signal to work. Here’s Wikipedia on erbium-doped fiber amplifiers: > A relatively high-powered beam of light is mixed with the input signal using a wavelength selective coupler (WSC). The input signal and the excitation light must be at significantly different wavelengths. The mixed light is guided into a section of fiber with erbium ions included in the core. This high-powered light beam excites the erbium ions to their higher-energy state. When the photons belonging to the signal at a different wavelength from the pump light meet the excited erbium ions, the erbium ions give up some of their energy to the signal and return to their lower-energy state. https://en.wikipedia.org/wiki/Optical_amplifier https://en.wikipedia.org/wiki/Optical_amplifier
wiml 2y ago
I think they're mostly laser amplifiers these days. So they're agnostic to modulation or WDM. But I assume there's still a noise/gain tradeoff.

ductsurprise 2y ago

Reminds me of the early dialup to DSL communication over standard telephone lines evolution.

nradov 2y ago

You're referring to single continuous fiber optic cables on land. Long undersea cables incorporate powered repeaters. Those can't be upgraded in situ with improved technology.

doikor 2y ago
They can just not really worth the hassle/money. You can pull the cable up and change them out if you want. Pulling a cable up, cutting a damaged part out of it and putting a new piece in is done all the time to fix damaged cables.
Suppafly 2y ago
would the repeaters need to be replaced? if you are compressing the data differently or sending it faster or whatever, I'm not sure the repeaters care, they are just amplifying the signal, not decoding it and resending it.