Undersea Cables

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A quick look in my lecture notes from last semester (uni's are usually pretty good at keeping figures upto date) it says:

"4th Generation - optical amplification and WDM (wavelength division multiplexing) - Submarine system - global network 250,000km capacity of 2.56Tb/s"
 
NathanE said:
That's impossible though. Think of the distance involved here. Even for light to travel the 4000 miles across the Atlantic it still takes probably 80ms or so. The extra 20ms or so comes from the heavily loaded routers on either side.
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Actually, it would take about 20ms for the light to travel 4000miles if my maths is correct - http://www.google.co.uk/search?q=6437376meters/c

Although that's also ignoring any delays from amplifiers.
 
What's to stop foreign countries / well-funded terrorists sending down divers or whatever and snipping a few cables?
 
blix said:
What's to stop foreign countries / well-funded terrorists sending down divers or whatever and snipping a few cables?
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Their usually laid pretty deep, not sure you could just dive down to them, obviously where they come ashore they'll be accessible, but I'd imagine they try to bring them ashore in friendly countries.
 
Nebzor said:
Wow. I thought it would've been easier to just replace some of it. Never realised it was more financially viable for them to fix it.
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4,000 miles of fibre optic cable and the time taken to lay it is going to be very pricy.
 
Nebzor said:
Wow. I thought it would've been easier to just replace some of it. Never realised it was more financially viable for them to fix it.
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I have no idea of the costs of fixing the cables or the total cost of relaying them, but my brother did some work in Australia a few years ago laying some large bundles of fibres and they costs well over £1million per mile, so id imagine replacing a whole undersea cable would be a very expensive job and would take a long time too.
 
Hmm interesting point about optical amplifiers

I'm pretty sure they use erbium doped fibres which don't need amplifiers. (The erbium does that part very well, 30db or so AFAIK)

Do any commercial tech companies use solitons for transmission yet? or is that still in lab. That would be good enough to go anywhere without amplification.

sid
 
sid said:
Hmm interesting point about optical amplifiers

I'm pretty sure they use erbium doped fibres which don't need amplifiers. (The erbium does that part very well, 30db or so AFAIK)

Do any commercial tech companies use solitons for transmission yet? or is that still in lab. That would be good enough to go anywhere without amplification.

sid
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edit/ my bad erbium needs pump lasers lol, I need to remember that by 18th may for my optical communications course.

sid
 
sid said:
edit/ my bad erbium needs pump lasers lol, I need to remember that by 18th may for my optical communications course.

sid
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I was just about to correct you on that. From my understanding (I had my exam 2 weeks ago, I hope it went well) There are Erbium doped amplifiers which use a high power 'pump' laser which puts the erbium electrons in a metastable state, the photons of the light pulse come along and stimulated emission of more photons (thus amplifying the signal).

Things to watch out for with erbium doped amplifiers are spontaneous emission generating noise and crosstalk.

Edit: I hope that didn't sound condescending or anything. I was reading it from the notes, I really didn't like the optical side of that module.
 
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dmpoole said:
NEXT QUESTION -

Every now and then you hear of these cables being snapped by an anchor or something and some are a very long way down.
How do they fix them?
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wiki said:
To effect repairs on deep cables, the damaged portion is brought to the surface using a grapple. Deep cables must be cut at the seabed and each end separately brought to the surface, whereupon a new section is spliced in. The repaired cable is longer than the original, so the excess is deliberately laid in a 'U' shape on the seabed. A submersible can be used to repair cables that lay at less depth.
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I know my uncle used to work on a boat doing this very job. He took me there one day and they had a submarine that they used with the cables (i don't know what for... repair work?) The submarine was wierd though, if I remember it had tracks...

Aero
 
Aero said:
I know my uncle used to work on a boat doing this very job. He took me there one day and they had a submarine that they used with the cables (i don't know what for... repair work?) The submarine was wierd though, if I remember it had tracks...

Aero
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I saw a programme about building some wind turbines off the coast of Denmark (I think), the boat they used to lay the power cables had a submarine with tracks, it was used to dig a trench in the seabed and lay the cable in it. The one you remember might be something similar.
 
geuben said:
I was just about to correct you on that. From my understanding (I had my exam 2 weeks ago, I hope it went well) There are Erbium doped amplifiers which use a high power 'pump' laser which puts the erbium electrons in a metastable state, the photons of the light pulse come along and stimulated emission of more photons (thus amplifying the signal).

Things to watch out for with erbium doped amplifiers are spontaneous emission generating noise and crosstalk.

Edit: I hope that didn't sound condescending or anything. I was reading it from the notes, I really didn't like the optical side of that module.
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Nope its cool.

I knew that for like 10 mins after the lecture lol. I need to revise all that material again.
 
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