[time-nuts] Photodiodes for high frequency OPLL

Attila Kinali attila at kinali.ch
Sun Mar 31 08:52:06 EDT 2013


On Sat, 30 Mar 2013 20:45:43 +0000
David Kirkby <david.kirkby at onetel.net> wrote:

> Fulll thesis here
> http://www.medphys.ucl.ac.uk/research/borl/docs/dkirkby.pdf
>
> I have seen systems where one sinusoidally modulates the voltage of a
> photomultipler tube. You could do the same with an APD. Then it acts a
> a mixer. Essentially
> 
> 1) Modulate laser at 100 MHz
> 2) Modlulate the APD bias voltage at 100.01 MHz
> 3) Detect light from laser on an APD.
> 4) Output of the APD is a sine wave at 10 kHz.
 

Thanks! I had a short look at your thesis and i think the idea
is not bad. I would need to calculate/simulate what that actually does.
 
> > There has been a similar idea around, using a third laser that
> > is pulsed with the desired offset frequency.
> 
> I was wondering if it could be done in more than one stage. A bit like
> a superhetrodyne receiver.

Probably. But as steep filters for optics are kind of hard to come by,
i think a super heterodyne design isn't realy going to work.

But probably using an APD with gain modulation at 1GHz or so, i could
down modulate the signal to something that is easier to handle
(ie something similar as a direct conversion software defined radios).

I wonder if this would work with normal PIN photodiodes as well, as
their price is much lower than APDs.

			Attila Kinali

-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
		-- unknown


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