[Laser] Re: Optical feedback for transimpedance amplifier

[Tim Toast]

Kerry, this looks exactly like what your looking for. 


optical feedback post:
http://groups.yahoo.com/group/Optical_DX/message/154

"Hello,

I have been reading quite a bit about low-light photodiode
amplifiers, in the hope of building a detector circuit for
a
scientific application that would normally call for
high-cost PMT or APD or SPM systems. I came across a rather
unusual paper, with an interesting variation of the typical
photodiode transimpedance amplifier concept. Rather than
using a very high resistance feedback resistor, the
feedback pathway was constructed using optical components.
An LED was driven by the op amp output, which then put a
small number of photons back onto a photodiode that was
wired head-to-tail with the signal receiver photodiode. The
optical coupling was weak, in that only a small fraction of
the photons emitted by the LED were gathered and directed
to the feedback photodiode. I posted a paper on this
concept in the 'files' section, as well as the datasheet
for the SFH229 photodiode, which has low capacitance and
very low NEP, and yet is available at a low cost from
Digikey and others.

Take care,

JHS"

------------------snip---------------------

i saw the paper in their members-only files section and it
looked similar to one of these below more or less:

Optical receiver employing 850 nm feedback - Electronics
Letters
LED. AIGaAs/Si feedback was chosen for low cost and to ...
‘An optical feedback transimpedance receiver for high
sensitivity ...
ieeexplore.ieee.org/iel1/2220/433/00008325.pdf - Similar
pages

the paper?:
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/50/224/00004007.pdf?arnumber=4007

possibly related paper:
http://www.freepatentsonline.com/5075794.html

a page from google books:
http://books.google.com/books?id=x9dKG1yY3i8C&pg=PA81&lpg=PA81&dq=%22optical+feedback%22+led+receiver&source=web&ots=msdlRJaCNx&sig=49xukuLi7p-Qco_p16GvgZOdbrM&hl=en

from prior art database:
http://www.priorartdatabase.com/IPCOM/000051442/


Another thing about using an LED to shine directly on a
detector, it seems to restore the sensitivity of
phototransistors that they loose in near darkness
conditions, compared to when they are used with a little
background light as in dusk or daylight. I guess in this
case though, the LED is just biasing the phototransistor to
a more sensitive point and not any kind of true feedback
(unless it was modulated with some of the same signal the
main detector is seeing).




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