[time-nuts] Photodiodes for high frequency OPLL

Attila Kinali attila at kinali.ch
Sat Mar 30 07:48:01 EDT 2013


I'm currently reading up some stuff on optical PLLs and am stuck with some
details i cannot find any data on.

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.
The only photodiodes that go higher are those for the telecom range
at 1-1.5um, which is a bit low for my needs.

But, i have seen descriptions of such OPLL that work with multi GHz
offsets in the 700-800nm range.

Now the question is: Do these use special made photodiodes with a very
high transition frequency or do they just treat the transition frequency
as a 3dB point and amplify the signal after detection?
(They do not describe the detection circuit at all, so i guess it must
be something readily available)

If it's the former, any idea where i could get such photodiodes?

If it is the later, how much damping can i assume with PIN or avalanche
photodiodes per decade?

Thanks in advance!

			Attila Kinali

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

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