[time-nuts] Photodiodes for high frequency OPLL

Peter Monta pmonta at gmail.com
Sat Mar 30 12:47:26 EDT 2013

Hi Attila,

> 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.

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.


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