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

[Dave Brown]

Let's know if they get to the bottom of this, Magnus- its interesting to 
speculate on the cause but hopefully they figure out the real issue.
 DaveB, NZ

----- Original Message ----- 
From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Cc: <magnus at rubidium.se>
Sent: Wednesday, August 24, 2016 11:06 AM
Subject: Re: [time-nuts] Optical link connects atomic clocks over 1400 km of 
fibre


> 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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