[time-nuts] HP 10811A/B OCXO OP/SRV manual is onlineathparchive.com AND HP 5501B manual.

[Jack Hudler]

Hmm. I think I have all the parts for this. Except the programmable polarizer.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf
Of Magnus Danielson
Sent: Tuesday, November 07, 2006 7:11 PM
To: bruce.griffiths at xtra.co.nz
Cc: time-nuts at febo.com
Subject: Re: [time-nuts] HP 10811A/B OCXO OP/SRV manual is onlineathparchive.com
AND HP 5501B manual.

From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] HP 10811A/B OCXO OP/SRV manual is onlineathparchive.com
AND HP 5501B manual.
Date: Wed, 08 Nov 2006 13:56:38 +1300
Message-ID: <45512B46.8090307 at xtra.co.nz>

> Magnus Danielson wrote:
> > From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> > Subject: Re: [time-nuts] HP 10811A/B OCXO OP/SRV manual is
onlineathparchive.com AND HP 5501B manual.
> > Date: Wed, 08 Nov 2006 11:25:44 +1300
> > Message-ID: <455107E8.1020201 at xtra.co.nz>
> >
> >   
> >> To measure the Allan variance you need at least 2 (preferably more) 
> >> stabilised lasers and a mixer (photodiode) plus a suitable amplifier to 
> >> produce a beat signal for analysis.
> >> The beat frequency may be as high as 100 MHz with a pair of 5501s 
> >> (frequency/wavelength accuracy of 0.1ppm) so the photodiode and 
> >> associated amplifier will need adequate bandwidth.
> >>     
> >
> > It seems like three 5501s, optical splitters/joiners and a fairly normal
> > counters should allow for a three-cornered hat and then should the Allan
> > variance and friends be possible to measure.
> >
> > Cheers,
> > Magnus
> >
> >   
> Things to watch out for when attempting to mix optical frequencies.
> 
> Orthogonally linearly polarised beams incident on a photodiode (or other 
> photodetector) will not produce a beat note.

Which is quite natural IF you think about it.

> A polariser in front of the diode with its transmission axis aligned so 
> that the transmitted beam intensities are approximately equal for each 
> of the 2  orthogonally polarised beams will allow a beat note to be 
> produced. For identical incident beam intensities the polariser 
> transmission axis will be at 45 degrees to the plane of polarisation of 
> either beam.
> 
> The angle (in radians) between the 2 beams has to be much smaller than 
> /l/d./
> where /l /is the wavelength and /d/ is the effective detector diameter.
> e.g. when /d/ = 1mm and /l/ = 633nm
> then the angle between the 2 beams must be << 2 arc minutes.

Yes, but if they where being brought together in a fused optical fibre
splitt/merge and one of the beam is adjusted through a mouse-ear assembly or
programable polarizer (fancy mouse-ear), then that problem wouln't be that much
of a problem? I think I have a bunch of suitable PIN diodes lying around doing
nothing good. But then again, I don't have a suitable set of lasers to check,
unless you count the DWDM lasers also lying around. :)

Thanks for the heads-up.

Cheers,
Magnus

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