4 ms·
1) The fibre pairs are housed in multiple layers of armor to protect against the elements, supply power to inline amplifiers and -most notably- provide the stru
by lb1lf 8y ago
1) The fibre pairs are housed in multiple layers of armor to protect against the elements, supply power to inline amplifiers and -most notably- provide the structural strength needed to survive being deployed. Outside diameter is still less than one inch, though.
2) Depends, but a metre or two (tops!) would be the right ballpark.
3) Not a dumb question; while loss in fibre optic cable is very low, repeaters are installed at regular intervals along the cable. they are powered by high-voltage DC supplied through the cable armor. The ocean acts as the return path.
4) Lots.
- bogomipz 8y ago>"3) Not a dumb question; while loss in fibre optic cable is very low, repeaters are installed at regular intervals along the cable. they are powered by high-voltage DC supplied through the cable armor. The ocean acts as the return path." That's incorrect, amplification is done via Erbium doping, it is part of the core of the cable. There are no external repeaters.
- lb1lf 8y ago...but the erbium doping is only part of the equation, involving additional circuitry powered from the surface? Or have I misunderstood completely?
- turboman 8y agoSo to clear this up a bit. EDFAs (which are the in-line amplifiers which use erbium doping) work by having a section of a fiber doped with erbium ions. Only the part which is going to amplify the signal is doped, the rest of the fiber is supposed to be as clean as it gets. Those erbium ions get shot with a laser (that's the part that needs power from the shore) and get excited. The source signal then hits the ions, which then emit more photons of the same exact properties, but just way more of them - therefore the amplification part. Continue 80km down the line, and the same thing has to happen again, as enough light has been attenuated. I mostly work with land systems, where the EDFAs are pieces of equipment completely separated from the fiber - you get a normal strand of fiber dug into the ground, and once you want to amplify it, you've got to plug it into an EDFA line card with the erbium-doped fiber already contained in it. In the sea, those systems are way more integrated and the fiber is usually spliced right into the amplifier. I might be able to dig up a card tomorrow if you're curious as to how the system looks.
- turboman 8y ago3) is wrong. The amplifiers are powered by DC, but one side of the fiber provides positive voltage and the other negative - the ocean is not a part of the circuit.
- lb1lf 8y ago-You are right; I just looked it up. I guess (not that it makes much of a difference!) I picked this up from a book on earlier days of submarine cables. Thanks!
- oasisbob 8y agoI was under the impression that cable systems are best understood as constant-current systems. As a side effect of this, they can withstand a power failure at either end, in which case the ground path is part of the circuit. (Essentially "single rail" operation.) If nothing else, both ends still share a common ground reference, yeah? https://pdfs.semanticscholar.org/3c72/998ffe9c39a1aa4a9faba42c04dbb33765aa.pdf https://pdfs.semanticscholar.org/3c72/998ffe9c39a1aa4a9faba4... Edit: thinking about this more, it seems quite obvious that you need a current return path regardless. If it's not the ocean/earth - what is it?