[time-nuts] Fast than light neutrino

Joe Gwinn joegwinn at comcast.net
Mon Sep 26 12:46:31 UTC 2011

At 6:56 AM +0000 9/26/11, time-nuts-request at febo.com wrote: (really Javier S)
>Date: Mon, 26 Sep 2011 08:56:12 +0200
>From: Javier Serrano <javier.serrano.pareja at gmail.com>
>To: Discussion of precise time and frequency measurement
>	<time-nuts at febo.com>
>Subject: Re: [time-nuts] Fast than light neutrino
>	<CAHBYzfTSx=jMKg218Sy6F9ji93OAht2=60w9_YY74-G-bkHGEA at mail.gmail.com>
>Content-Type: text/plain; charset=ISO-8859-1
>  >
>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

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 

Joe Gwinn

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