[Laser] What do you guys need??? (APDs).

[Steve J. Noll]

Joe Fitzgerald [ jfitzgerald@alum.wpi.edu ] wrote:
> 
> How about the specification for the shunt resistance of your 020-72-60-541
> APD?  I was fooling around with the spreadsheet you told us about the other
> day, and could not find this spec in your catalog.

Shunt resistance is not specified for APDs because they are always
operated
biased (highly biased, at that!)  Shunt resistance is measured by
applying
+10mV and -10mV and measuring the current at each of those voltages. 
The
shunt resistance is then 0.02 divided by the difference between the two
currents.  It doen't really have a meaning for APDs, dark current is
more
important.

> Also, your Perkin Elmer talks about using APD's in Geiger mode - above the
> breakdown voltage with max current limited to less than 50 microamps.  Can
> your APD's be run in this mode and if so can we use this for lasercom?  I am
> working on a receiver for the laser on AMSAT OSCAR 40,  and have precious
> few photons per bit to deal with.

They probably could, but I believe the Perkin Elmer devices are very
very special,
ultra low dark current, with a very small active area.  I heard a rumor
that
they really aren't shipping them, but I can't verify that.  I believe
that if
the dark current isn't especially low that it might be pointless to
operate in
Geiger mode (past breakdown with a current limiting resistor so the
detector
isn't smoked.)

I just had a conversation with one of our engineers who worked primarily
on
large area APD development.  I told him what I remembered seeing on one
of the
web sites about the AO-40 laser budget.  He figured there would result
something
in the order of 100 photons/sq-cm - which sounds encouraging.
Is that figure in the ballpark?

Steve WA6EJO


> -Joe KM1P
> 
> ----- Original Message -----
> From: "Steve J. Noll" <WA6EJO@big-list.com>
> To: <laser@mailman.qth.net>
> Sent: Thursday, January 10, 2002 9:25 PM
> Subject: [Laser] What do you guys need???
> 
> > Hi Guys:
> >
> > I've been trying to figure out how I can help the group
> > and promote Amateur Radio Laser experimenting...
> >
> > As you may know I was pretty active big-time long ago, but
> > have been out of it for quite a while.  There's no one here
> > to play with and I kinda get my fill of it at work.
> >
> > I've been working at Advanced Photonix - a major silicon
> > photodiode manufacturer for the last ten years and am now
> > head of test engineering and manufacturing engineering.
> > So, I have access to certain "things."
> >
> > I wish I could give away stuff like our large area avalanche
> > photodetectors, but unfortunately that's out of the question -
> > they are quite expensive.  But, I could characterize your
> > photodiodes for you - like for responsivity, NEP, rise time,
> > dark current, etc., and I might be able to come up with some
> > PIN photodiode 'blems'.
> >
> > What is there a need for?
> >
> > 73,
> >
> > Steve WA6EJO
> >
> > --
> > Steve J. Noll | Ventura California | sjnoll@big-list.com
> >               | The Used Equipment Dealer Directory:
> >               | http://www.big-list.com
> >               | The Peltier Device Information Site:
> >               | http://www.peltier-info.com