[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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