[time-nuts] OT: transfer of 3 GHz via fiber optic

[Dr Bruce Griffiths]

Didier Juges wrote:
> This is somewhat off topic, but still a matter of precision timing.
>
> A friend of mine wants to send a 3 GHz LO signal up a fiber optic cable.
>
> I know there have been threads dealing with transmission of precise 
> timing signals over fiber optics, and I hope I can get some suggestions 
> where to look for more info.
>
> I have found lots of links to high data rate laser transceivers, but 
> while they all tout the high data rate, there is little specified about 
> delay, and jitter is not very good, so it seems as a minimum he would 
> need a clean-up PLL at the receive end. My initial recommendation was to 
> send a precise 10 MHz (where did that come from?) via coax and have a 
> synthesizer at the receive end, but he is trying to minimize the amount 
> of hardware there.
>
> Thanks in advance,
>
> Didier KO4BB
>
>
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>   
Didier

Radio telescope antenna arrays typically distribute the reference 
frequency to the various antennae by modulating a diode laser.
They also compensate for fibre delay variations by sending a signal back 
to the source where its phase is compared with the original.
Fibre stretchers etc are used to compensate the delay.

http://www.tuc.nrao.edu/~bshillue/OFTMAG_Shillue.pdf 
<http://www.tuc.nrao.edu/%7Ebshillue/OFTMAG_Shillue.pdf>

http://www.cv.nrao.edu/~avaccari/tuceng/photonics/documentation/conferences/data/mwp99.pdf 
<http://www.cv.nrao.edu/%7Eavaccari/tuceng/photonics/documentation/conferences/data/mwp99.pdf>

http://www.alma.nrao.edu/memos/html-memos/alma440/memo440.pdf

http://www.tuc.nrao.edu/~bshillue/loref-mwp2004.pdf 
<http://www.tuc.nrao.edu/%7Ebshillue/loref-mwp2004.pdf>

http://www.aoc.nrao.edu/evla/geninfo/memoseries/evlamemo105.pdf

http://www.cv.nrao.edu/~awootten/mmaimcal/ALMAOuterLimits.pdf 
<http://www.cv.nrao.edu/%7Eawootten/mmaimcal/ALMAOuterLimits.pdf>

http://www.cv.nrao.edu/~avaccari/tuceng/photonics/documentation/presentations/data/mwp99.pdf 
<http://www.cv.nrao.edu/%7Eavaccari/tuceng/photonics/documentation/presentations/data/mwp99.pdf>

In your friends case if the relative phase of the signal at both ends of 
the cable isn't too important then simply modulate the at 3 GHz, The 
3GHz will be be generated by the photodiode at the other end which acts 
as a photomixer mixing the laser frequency and the laser frerquency + 
3GHz components. Yes a phase locked loop cleanup oscillator (DRO?) will 
be required at the receiver end. The laser frequency need not be 
stabilised as fluctuations in the laser frequency will cancel at the 
photomixer.

You need an analog modulator and an analog photodetector + amplifier 
link digital links are not suitable.


Bruce