A New TransAtlantic Cable System

Mon Oct 4 17:41:16 UTC 2010

On 10/4/2010 1:24 PM, Heath Jones wrote:
>> By the way, my recollection is the undersea regenerators do purely optical regeneration.
>> There is no O-E conversions undersea, only at the landing stations and terrestrial components.
> 
> I'm not clever enough to know of some way that you could do optical
> regeneration without converting the signal to electrical and
> retransmitting back as optical.. How is that done?
> 
> 

A halfway-decent description of the physics of how this is done, is
covered in Neal Stephenson's excellent article on Wired:

http://www.wired.com/wired/archive/4.12/ffglass.html

The specific page covering optical regeneration:

http://www.wired.com/wired/archive/4.12/ffglass.html?pg=6&topic=

quote:

====
These signals begin to fade after they have traveled a certain distance,
so it's necessary to build amplifiers into the cable every so often. In
the case of FLAG, the spacing of these amplifiers ranges from 45 to 85
kilometers. They work on a strikingly simple and elegant principle. Each
amplifier contains an approximately 10-meter-long piece of special fiber
that has been doped with erbium ions, making it capable of functioning
as a laser medium. A separate semiconductor laser built into the
amplifier generates powerful light at 1,480 nm - close to the same
frequency as the signal beam, but not close enough to interfere with it.
This light, directed into the doped fiber, pumps the electrons orbiting
around those erbium ions up to a higher energy level.

The signal coming down the FLAG cable passes through the doped fiber and
causes it to lase, i.e., the excited electrons drop back down to a lower
energy level, emitting light that is coherent with the incoming signal -
which is to say that it is an exact copy of the incoming signal, except
more powerful.

====

Cordially

Patrick Giagnocavo
patrick at zill.net