3 ms·

Does the light signal in an fibre optic cable get noisy over distance? If so, then wouldn't an analog signal amp such as this simply amplify the noise along wit

Does the light signal in an fibre optic cable get noisy over distance? If so, then wouldn't an analog signal amp such as this simply amplify the noise along with the signal? Decoding and re-encoding would have the effect of 'cleaning' the signal in this case. If it does get noisy, where does the noise come from? The medium? Leakage from outside the cable?

rusk 9y ago
I thought the point of fibre was that it was low noise ... EDIT There's a good discussion of what you're talking about here [0] Upon further reading, there's a such thing as an all optical regenerator which would appear to provide the best of both worlds, though there's nothing here about how widely these are used [1] [0] http://www.rfwireless-world.com/Terminology/Optical-Repeater-vs-Optical-Amplifier.html http://www.rfwireless-world.com/Terminology/Optical-Repeater... [1] https://en.wikipedia.org/wiki/Mamyshev_2R_regenerator https://en.wikipedia.org/wiki/Mamyshev_2R_regenerator
- askvictor 9y ago
  That's pretty fascinating, but I don't understand how this works from a purely thermodynamic POV. If the signal is being amplified, where is the extra energy coming from? Does it deplete the material? Is it like boosting voltage at the expense of current?
  - amazon_not 9y ago
    Longhaul subsea fiber optic cables have a conductor in them that carries a high voltage DC current that powers the amplifiers on the cable route.
amazon_not 9y ago
> Does the light signal in an fibre optic cable get noisy over distance? Yes. > If so, then wouldn't an analog signal amp such as this simply amplify the noise along with the signal? Yes. That's why there are limits on the reach of amplified networks. > Decoding and re-encoding would have the effect of 'cleaning' the signal in this case. Yes, but regenerating the signal introduces complexity, and thus reduces reliability, adds latency and only works for a specific encoding, which makes upgrades impossible. None of these things are wanted at the bottom of the sea for the next 25 years. > If it does get noisy, where does the noise come from? There are lots of noise sources. See: http://www.svphotonics.com/pub/pub029.pdf http://www.svphotonics.com/pub/pub029.pdf > The medium? Yes, partly. > Leakage from outside the cable? No. Although vibrations can cause noise.

rusk 9y ago

I thought the point of fibre was that it was low noise ... EDIT There's a good discussion of what you're talking about here [0] Upon further reading, there's a such thing as an all optical regenerator which would appear to provide the best of both worlds, though there's nothing here about how widely these are used [1] [0] http://www.rfwireless-world.com/Terminology/Optical-Repeater-vs-Optical-Amplifier.html http://www.rfwireless-world.com/Terminology/Optical-Repeater... [1] https://en.wikipedia.org/wiki/Mamyshev_2R_regenerator https://en.wikipedia.org/wiki/Mamyshev_2R_regenerator

askvictor 9y ago
That's pretty fascinating, but I don't understand how this works from a purely thermodynamic POV. If the signal is being amplified, where is the extra energy coming from? Does it deplete the material? Is it like boosting voltage at the expense of current?
- amazon_not 9y ago
  Longhaul subsea fiber optic cables have a conductor in them that carries a high voltage DC current that powers the amplifiers on the cable route.

amazon_not 9y ago

> Does the light signal in an fibre optic cable get noisy over distance? Yes. > If so, then wouldn't an analog signal amp such as this simply amplify the noise along with the signal? Yes. That's why there are limits on the reach of amplified networks. > Decoding and re-encoding would have the effect of 'cleaning' the signal in this case. Yes, but regenerating the signal introduces complexity, and thus reduces reliability, adds latency and only works for a specific encoding, which makes upgrades impossible. None of these things are wanted at the bottom of the sea for the next 25 years. > If it does get noisy, where does the noise come from? There are lots of noise sources. See: http://www.svphotonics.com/pub/pub029.pdf http://www.svphotonics.com/pub/pub029.pdf > The medium? Yes, partly. > Leakage from outside the cable? No. Although vibrations can cause noise.