[time-nuts] would an optical primary standard provide any general benefit?

Magnus Danielson magnus at rubidium.dyndns.org
Thu Apr 5 16:07:10 UTC 2012


On 04/03/2012 01:10 PM, Jim Lux wrote:
> On 4/3/12 12:49 AM, Azelio Boriani wrote:
>> Yes, but nonetheless why not develop more stable primary clock
>> sources? We
>> can always take care of the dissemination in the meantime and try to
>> develop a more precise time transfer method.
>>
>> On Tue, Apr 3, 2012 at 2:39 AM, beale<beale at bealecorner.com> wrote:
>>
>>> Having read this NIST review paper by Thomas E. Parker, "The uncertainty
>>> in the realization and dissemination
>>> of the SI second from a systems point of view"
>>> http://tf.boulder.nist.gov/general/pdf/2564.pdf
>>>
>>> ...it seems that any potential improvement in frequency standards (Cs
>>> fountain -> optical clocks) will not benefit most time/frequency users,
>>> because existing long-range time-transfer methods (TWSTFT and GPS
>>> carrier
>>> phase) are still limited to at best 2E-16 for 30-day averaging, and
>>> there
>>> is no generally practical way to improve them currently in sight. (Laser
>>> ranging of satellites being considered not generally practical). Just
>>> curious what people think, is this too pessimistic a view, or is it
>>> fair to
>>> say that having a 10x improved primary standard would not improve
>>> stability
>>> or accuracy for anyone outside of stabilized optical-fiber distance from
>>> such a standard?
>>>
>>>
>
>
> In general, as a technology developer, I agree with you, but the sources
> of money with which to develop technology often have a slightly
> different view.

I wonder if they have really reached the measurement limit possible in 
fibre systems.

If one is serious about pushing fibre based TT systems down, there is a 
number of techniques one could apply as an ensemble, but I have not seen 
any serious work, only working on different pieces of the puzzle.

Hence, I think the article may be premature in this respect.

Cheers,
Magnus




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