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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Jan 14 06:21:57 UTC 2015


Although the phase noise when using optical combs to generate Rf signals 
is low there is no mention of the am noise.

Bruce

On Tuesday, January 13, 2015 02:49:33 PM Tom Knox wrote:
> 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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