[Laser] LED used as APD

[Charles Pooley]

I read with interest the article re use of LEDs as avalanche detectors, but one fact seems missing:  The quantum effriciency of the diode itself.  For example, if at a voltage below the avalanche voltage so it operates as a photodiode, what would be the current from, say 10 microwatts of light focused so it falls on the sensitive area?  10%, 50%, more?  Si PIN diodes have typically 70%. 

And another:  the sensitive area.  Will there have to be a scanning experiment to map it?  

The article I got (from Tim, I think), says that some L:EDs work but blue ones did not because the dark current rose to high before the avalanche voltage was reached.  Would this work with various longer wavelength, and IR wavelengths?  850 nm, 940?

My interest is in the various wavelengths available with small diode lasers, both NIR and red.

Charles Pooley     Microlaunchers




________________________________
From: Tim Toast <toasty256 at yahoo.com>
To: Optical_DX at yahoogroups.com
Cc: laser at mailman.qth.net
Sent: Tue, January 26, 2010 11:35:43 PM
Subject: Re: [Laser] LED used as APD

With all the blue and UV led's out there, i bet a good match 
can be found for the 3371A nitrogen line. Relatively simple home
built nitrogen lasers that work in open air (TEA) make short 
nanosecond or even picosecond length pulses. A large beam 
spreading lens would be in order of course since these are high
peak power pulses.
tim
http://www.aladal.net/toast/exp.html

------------------------------------------------

On Wed, Jan 20, 2010 at 8:54 PM, Garnier Yves <f1avy at ...> wrote:
> So if I well understand this effect a blue LED used as detector 
>could be able to detect UV A ?

looks promising, sparks' emission spectra in open air peaks at 
337nm, the  superradiant nitrogen line. A significant portion 
of the energy could be detected by the blue led, which opens a 
path for spark signaling.
If UV leds can work in APD mode too one might want to try them 
and nitrogen lasers for very long range communications.
inverse <inverse at ...>
pagaiard 


Tim
I noticed an error in my last mail:
I want to write : "Unfortunately it seems that a LED diode used 
as photodetector receives a wavelenght slightly shorter than 
its own transmission wavelenght."
I confused wavelenght variations and frequency variations :-) !

So if I well understand this effect a blue LED used as detector 
could be able to detect UV A ?
Yves F1AVY
http://f1avyopto.wifeo.com


Tim
Unfortunately it seems that a LED diode used as photodetector 
receives a frequency slightly lower than its own transmission 
frequency. To receive a classical RED Luxeon you must use an 
other "deep red" LED.
The main interest seems to be only the low cost of the LED and 
its filter effect.
The avalanche effect seems too abrupt and instable for linear 
photodetection but it could be usefull for high speed light 
pulses detection if followed by threshold and pulse shaping 
circuitries.
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=RSINAK00006\
9000011003751000001&idtype=cvips&gifs=yes&ref=no
I have put my test circuit to test LED as photodetector in the 
photo album "F1AVY F8DO cloud bounce"
73
Yves F1AVY
http://f1avyopto.wifeo.com


Hi Yves,
That would certainly simplify transceivers and alignment if you 
could use the same LED to receive. That would put an end to the 
full-duplex though. Test one of those Luxeons and see how they 
perform in APD mode.
I was thinking, since the bandwidth is so much narrower than a 
regular photodiode, the LED-APD gain could actually be lower and 
still outperform one in the same bandwidth. I guess you could 
test them side by side with the photodiode bandwidth reduced 
with a filter to the same as the LED then you could compared 
their sensitivity in the same bandwidth.
tim
http://www.aladal.net/toast/exp.html
















      
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