You might take a look at these:
http://www.ebay.com/itm/360601919160?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_780wt_911
They have a fiber terminated Avalanche PD and built in HV supply from 5
volts. Cheap at $5 each.
Tom
----- Original Message -----
From: "J. Forster" <j...@quikus.com>
To: <li...@lazygranch.com>; "Discussion of precise time and frequency
measurement" <time-nuts@febo.com>
Sent: Saturday, March 30, 2013 1:52 PM
Subject: Re: [time-nuts] Photodiodes for high frequency OPLL
My understanding is that you want to operate photodiodes with high reverse
bias for the best frequency response. The bias widens the space charge
layer, thereby reducing the capacitance of the device. The high electric
fields in the SCL region also sweeps the hole-electron pairs, produced by
photon injection, out faster, hence improving the response as well. Such
devices are best operated with very low capacity wiring into a virtual
ground.
Of course, there are limits as, at some point, the device will avalanche.
When that ocurrs, the device will have gain akin to a photomultiplier.
Some devices are actually designed to operate in this mode, but, since the
thing is so near to unstable requires careful control of temperature and
oher parameters.
-John
================
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 <att...@kinali.ch>
Sender: time-nuts-boun...@febo.com
Date: Sat, 30 Mar 2013 12:48:01
To: <time-nuts@febo.com>
Reply-To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: [time-nuts] Photodiodes for high frequency OPLL
Moin,
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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