[time-nuts] Photodiodes for high frequency OPLL

lists at lazygranch.com lists at lazygranch.com
Sat Mar 30 13:29:45 EDT 2013

You lose me at damping per decade? Is damping the right word? Do you mean high frequency rolloff?

Most texts on photodiodes go into bootstrapping them to reduce the effect of capacitance. But if you design fully differential amplifier circuits, they have the same effect as bootstrapping. Jerald Graeme's "Photodiode Amplifiers" goes into this. I'm not a fan of Gain technology as a company, but Graeme's book are good texts. 

The bootstrapping circuits use simpler buffers to keep the voltage potential across the diode low, while the fully differential circuits depend on gain bandwidth product to do the same.

-----Original Message-----
From: Attila Kinali <attila at kinali.ch>
Sender: time-nuts-bounces at febo.com
Date: Sat, 30 Mar 2013 12:48:01 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: [time-nuts] Photodiodes for high frequency OPLL


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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