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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Aug 25 02:00:57 EDT 2016


You'd need a rather thick copper jacket to shield effectively against the 50Hz magnetic field.
Bruce
 

    On Thursday, 25 August 2016 3:00 PM, André Esteves <aifesteves at gmail.com> wrote:
 

 So the way to eliminate that perturbation would be to put a copper
jacket over it to attenuate the EM field?

André Esteves

2016-08-25 0:33 GMT+01:00 Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
> 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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