[time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bruce Griffiths]

The Kerr effect is Proportional to the square of the field so one would 
expect a strong 100Hz component from this.

The magneto optical Kerr eefect which rotates the plane of polarisation is 
linear however.

Bruce
On Wednesday, August 24, 2016 07:04:31 AM Bob kb8tq wrote:
> Hi
> 
> I would not rule out line noise into the electronic side of things.
> 
> Bob
> 
> > On Aug 23, 2016, at 7:06 PM, Magnus Danielson 
<magnus at rubidium.dyndns.org>
> > wrote:
> > 
> > Don't over-interpret the 50 Hz aspect, I don't remember those details 
from
> > 4.5 months back or so, as I already indicated. I can ask on the details
> > tomorrow. I think they discussed the Kerr effect:
> > https://en.wikipedia.org/wiki/Kerr_effect
> > The PTB folks asked me the same question essentially.
> > 
> > Would be nice to verify it.
> > 
> > Cheers,
> > Magnus
> > 
> >> On 08/24/2016 12:11 AM, David wrote:
> >> I could not find it in the links but Magnus mentions 50 Hz instead of
> >> 100 Hz.
> >> 
> >> I would expect a 100 Hz noise signal if it was vibration coupled from
> >> magnetostriction in a transformer; magnetostrictive strain depends 
on
> >> the magnitude of the magnetic field strength and not the sign which 
is
> >> why 50/60 Hz transformers hum at 100/120 Hz.  50 Hz however fits 
with
> >> piezomagnetism if the optical fiber was in an oscillating magnetic
> >> field and antiferromagnetic; for piezomagnetism, the strain does
> >> follow the sign.
> >> 
> >> https://en.wikipedia.org/wiki/Magnetostriction
> >> https://en.wikipedia.org/wiki/Piezomagnetism
> >> 
> >> I do not know if optical fibers are even slightly antiferromagnetic
> >> but maybe doping can make them susceptible?
> >> 
> >>> On Wed, 24 Aug 2016 09:31:57 +1200, you wrote:
> >>> 
> >>> What is the coupling mechanism giving rise to the 50Hz 
disturbance?
> >>> DaveB, NZ
> >>> 
> >>> ----- Original Message -----
> >>> From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
> >>> To: <time-nuts at febo.com>
> >>> Cc: <magnus at rubidium.se>
> >>> Sent: Wednesday, August 24, 2016 8:54 AM
> >>> Subject: Re: [time-nuts] Optical link connects atomic clocks over 
1400
> >>> km of fibre
> >>> 
> >>>> ...
> >>>> 
> >>>> These links is in principle not very complex, but they are 
regardless
> >>>> somewhat sensitive. One link experienced excessive 50 Hz 
disturbance,
> >>>> which they could trace to the fact that for a short distance the 
fibre
> >>>> was
> >>>> laying alongside the house 400V three-phase feed-cable with 
quite a bit
> >>>> of
> >>>> current in it.
> >>>> 
> >>>> ...
> >>>> 
> >>>> Cheers,
> >>>> Magnus
> >> 
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