4 ms·

It's not really the fibre that slows down the signal as much as the opto-electrical repeaters that relay the signal many times as it travels vast distances. Li

It's not really the fibre that slows down the signal as much as the opto-electrical repeaters that relay the signal many times as it travels vast distances. Light can only go a few km before it needs to be boosted

datenwolf 8y ago
This is wrong on both accounts. The speed of light in a fiber is only about 70% of speed of light in vacuum. Modern single mode fiber has very low attenuation (less than 0.01dB/km). But more importantly you don't have to use opto-electrical repeaters to boost the signal. What you do is using purely passive dispersion control by mixing different kinds of fiber and compensate for the rest dispersion using chirped fiber bragg gratings. To boost the signal you splice in rare earth doped fibers (Erbirum, Yttrium) which acts as optically pumped optical amplifier.
- diggerNick6771 8y ago
  Well, I stand corrected. I had read several articles about undersea fibre and they said that it required a repeater every few km. Looking this up, it says that modern cables can go upward of 100 km between repeaters. Across the Atlantic that still adds up though, if my electro-optical assumption were true. Second, I guessed that it was electro-optical because I know the cables carry voltage to power the repeaters. I just wasn't aware that continuous amplification was even possible, especially at the extremely high bit rates that fibre runs at. Thank you for the correction.
- zoggenhoff 8y ago
  When you write "modern" how long ago would that have been installed? /me trying to get a handle on optical development.
  - datenwolf 8y ago
    The basic principle has been invented over 30 years ago in 1987: https://ieeexplore.ieee.org/document/4258955 https://ieeexplore.ieee.org/document/4258955 They're used in long haul communication for some 15 years or so. They're especially useful in submarine cables, for the sole reason, that new optical transmission schemes(modulation, wavelength multiplexing and so on) can be implemented by just replacing the equipment on either end, without the need to replace components down there on the seabed.

datenwolf 8y ago

This is wrong on both accounts. The speed of light in a fiber is only about 70% of speed of light in vacuum. Modern single mode fiber has very low attenuation (less than 0.01dB/km). But more importantly you don't have to use opto-electrical repeaters to boost the signal. What you do is using purely passive dispersion control by mixing different kinds of fiber and compensate for the rest dispersion using chirped fiber bragg gratings. To boost the signal you splice in rare earth doped fibers (Erbirum, Yttrium) which acts as optically pumped optical amplifier.

diggerNick6771 8y ago
Well, I stand corrected. I had read several articles about undersea fibre and they said that it required a repeater every few km. Looking this up, it says that modern cables can go upward of 100 km between repeaters. Across the Atlantic that still adds up though, if my electro-optical assumption were true. Second, I guessed that it was electro-optical because I know the cables carry voltage to power the repeaters. I just wasn't aware that continuous amplification was even possible, especially at the extremely high bit rates that fibre runs at. Thank you for the correction.
zoggenhoff 8y ago
When you write "modern" how long ago would that have been installed? /me trying to get a handle on optical development.
- datenwolf 8y ago
  The basic principle has been invented over 30 years ago in 1987: https://ieeexplore.ieee.org/document/4258955 https://ieeexplore.ieee.org/document/4258955 They're used in long haul communication for some 15 years or so. They're especially useful in submarine cables, for the sole reason, that new optical transmission schemes(modulation, wavelength multiplexing and so on) can be implemented by just replacing the equipment on either end, without the need to replace components down there on the seabed.