[time-nuts] Photodiodes for high frequency OPLL

Attila Kinali attila at kinali.ch
Sat Mar 30 14:31:00 EDT 2013

Moin Peter,

On Sat, 30 Mar 2013 09:47:26 -0700
Peter Monta <pmonta at gmail.com> wrote:

> > The goal is to make two lasers locked with about 7GHz of offset to
> > eachother.
> >
> > So far, i figured out that PIN photodiodes can go up to several 100MHz
> > transition frequency and avalanche photodiodes are available up to 2GHz.
> >
> If you need photodiode response only near 7 GHz, as seems likely, then
> maybe the reactance of the 2 GHz diode can be tuned out with some sort of
> matching circuit in the hope of getting usable response near 7 GHz.  Better
> and simpler to get a diode with flat response all the way from DC to 7 GHz,
> though, of course.

Yes, but they are not available. At least i have not been able to
locate any in the 700-800nm range.

> Depending on the application, you might be able to tolerate pretty high
> mixer losses, as you mention, but if you do need the best possible SNR, an
> I/Q configuration would give slightly lower noise at the cost of two diodes
> and amplifiers.

What do you exactly mean by I/Q mixing here? Using two beam paths
with 90° out of phase onto two photodiodes? If i'm not mistaken
this will still lead to 7GHz mixing signal, which i have to get out
of the diodes.

				Attila Kinali

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

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