At 6:56 AM +0000 9/26/11, time-nuts-requ...@febo.com wrote: (really Javier S)
Date: Mon, 26 Sep 2011 08:56:12 +0200
From: Javier Serrano <javier.serrano.par...@gmail.com>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] Fast than light neutrino
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<CAHBYzfTSx=jMKg218Sy6F9ji93OAht2=60w9_yy74-g-bkh...@mail.gmail.com>
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[snip]
>
I did not express myself correctly. We know how to do accurate two-way sync
over a few km of fiber. See e.g.
http://dl.dropbox.com/u/13409775/pac2011/WEOAN1.pdf or
http://dl.dropbox.com/u/13409775/wrapper.pdf (our contribution to the CLIC
Conceptual Design Report).
Thanks for the reports.
What is new for us is going through more than
1000 km of fiber (only neutrinos have the luxury of going in a straight line
through the crust of the Earth, 732 km). I wonder who one calls for fibers
and also more technical things like optical amplifier technology with
typical ranges, etc. What I gather from the discussion so far is that 100 km
is within reach of available optical transceivers. I wonder how far one can
go with EDFAs.
EDFAs can easily achieve 10 dB or running closer to the edge 20 dB of
gain, all with no electronics delay, but EDFAs are quite noisy, so
there is a tradeoff to be made.
EDFAs are inherently bidirectional, although they usually contain an
optical circulator to make them unilateral. But it would not be hard
to make EDFAs that amplified in one direction for one wavelength, and
in the opposite direction at a different (but nearby) wavelength.
And one can also have a command wavelength, to allow for commanding
of direction reversals and the like, so the fiber companies
involvement is limited to hosting and installation of equipment.
One thing we could do is establish a fiber link between METAS
in Bern and CERN, and then look for a good metrology place in Rome (the
national one in Italy is in Torino I believe) and have a link between them
and Gran Sasso. Then we could use their UTC data sets to establish a paper
link between CERN and Gran Sasso which would be independent of the current
link.
Why do all that, versus just running an amplified fiber between CERN
and Gran Sasso? Two links are likely to be twice the trouble and
error.
Joe Gwinn
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