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

[Dr Bruce Griffiths]

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.
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.

Bruce