On 11/21/2011 09:49 AM, Hal Murray wrote:
[email protected] said:
I heard on the BBC the other day that a repeat experiment is planned,
firing neurinos from the US into Canada. The labs were not cited, but I
expect it would be Fermilab to Sudbury Ontario. If this is the case, then
there will still be the problem of not being able to run a parallel fibre
as the Sudbury detectors are also deep underground. ...
I don't think that running a parallel fiber will help much. I see two
problems.
First, fibers don't run in straight lines. Even if you could accurately
survey the pipes in the ground, there is slack in the fiber within the cable
bundle so it doesn't break if somebody pulls on the cable.
Second, the speed of light in fibers isn't known to the required level of
accuracy. (It's probably temperature dependent.)
It is. About 10% of the change is due to length-changes in the fibre and
about 90% of the change is due to group-delay shifts in the fibre.
If you laser frequency (wavelength is the traditional value here) shifts
then the dispersion effect also causes shift in delay.
In the context of fibers, having the detectors located deep underground in
not a problem. They have to get power and data cables down to the
instruments somehow. It would be easy to run a fiber in parallel with those
cables.
There is also the delay in the amplifiers that you will need every 100 miles
or so. Or the low rise time if you try to avoid the amplifiers because you
don't need much bandwidth...
Depends on the amplifiers you are using. EDFA amps has fairly high
bandwidth and delay is like normal fibre of the same length.
Cheers,
Magnus
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