[time-nuts] Current state of optical clocks and the definition of the second

[Tom Knox]

I think the key to this concept is an optical comb filter.  
Archita Hati of the Phase Noise measurement Group at NIST has been 
researching ultra low phase noise 5MHz references using an optical standard and comb filter 
as well as extensive RF components to down converting to the desired frequency. 
In experiments I believe she has achieved phase noise better then -154db @ 1Hz offset. 
It does appear to be the future but currently is far to large and complex for most if any 
practical use. I believe this link is the paper by Archita Hati I referred addressing 
State-of-the-Art RF Signal Generation From Optical Frequency Division. 
http://tf.boulder.nist.gov/general/pdf/2646.pdf
Enjoy;
Thomas Knox

Thomas Knox



> From: namichie at gmail.com
> Date: Wed, 14 Jan 2015 07:00:09 +1100
> To: time-nuts at febo.com
> CC: namichie at gmail.com
> Subject: Re: [time-nuts] Current state of optical clocks and the definition	of the second
> 
> 
> THe stability /accuracy of lasers is entirely dependent on the cavity length.
> Materials used are usually invar or silica, so you are no better off than 
> with a quartz crystals.
> They are just a resonant cavity.
> cheers, 
> Neville Michie
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