[time-nuts] sub cables

Magnus Danielson magnus at rubidium.dyndns.org
Thu May 1 19:44:26 EDT 2008

From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] sub cables
Date: Fri, 02 May 2008 10:47:03 +1200
Message-ID: <481A4867.8040307 at xtra.co.nz>

> Magnus Danielson wrote:
> > From: Scott Mace <smace at intt.net>
> > Subject: Re: [time-nuts] sub cables
> > Date: Thu, 01 May 2008 16:30:43 -0500
> > Message-ID: <481A3683.4050300 at intt.net>
> >
> >   
> >> A repeater or regen goes optical-electrical-optical.  I think you are
> >> talking about an EDFA.  While it may pass light when it's down, one
> >> has to take into account the optical budget of the span.
> >>     
> >
> > Modern sub cables does not used a distributed line of EDFAs anymore. They use
> > the entire cable length as an amplifier instead. If the laser is down, you can
> > reach it and service it, since it sits on dry land anyways.
> >
> > I have an EDFA lying around my office desk. Never know when I need one.
> > Uses a 250 mW 850 nm pumping laser.
> >
> > Cheers,
> > Magnus
> >
> >   
> Magnus
> There is a limit to the cable length when using EDFAs above which a 
> regenerator is required.

Certainly, unless you go soliton system.

Also, long stretches of EDFA fibers is usually using dispersion compensation
fibers, which provides an matching anti-group-delay to force the dispersed
frequencies back into place and thus reshaping. The reshaping abilities have
advanced significantly.

EDFA also has an interesting shift in frequency for each amplification.

There are now very long cables systems which is all optical from shore to shore
such that any 3R is on shore and not wet. For instance, the TAT-14 cables is
all-optical trans-atlantic. The PC-1 trans-pacific cable, a 21000 km run, is
also all-optical.

They are laying a new trans-pacific cable now, it should be ready just prior to
the Being olympics.

This is standard buissness now.


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