[Laser] 5 mW lasers & LEDs - Detectors

[Steve J. Noll]

As far as silicon photodiodes go, they are all about the same.  They can 
be made red-optimized, blue-optimized, and UV-optimized, low noise 
optimized, speed optimized, different active areas, etc.,
but all have absolute spectral responsivities in the area of 0.5 to 0.7 
A/W, peaking around 900 to 1000 nm.
There's no magic formula to make one twice, let alone ten times better, 
at any wavelength we'd be interested in as compared to the average 
silicon photodiode.
It's kind of a law of physics thing.
Best optimization is big collection optics (hey, just like radio!) and a 
detector of such size that it can see all that's collected.
And.. optical bandpass filtering if there's going to be any interfering 
light.
Probably signal processing too. I've made highly accurate measurements 
of photodiodes using lock-in amplifiers, really pulls signals out of the 
mud.
LEDs as detectors provide inherent filtering near their emission 
wavelength, but I think a real photodiode has better absolute spectral 
responsivity.
Opto Diode used to make LEDs optimized for detection. Not sure they do 
any more.
The industry trend instead has been "filter-on-die," evaporating 
bandpass filters directly on silicon photodiode die yielding a good 
detector at whatever wavelength you want.

73,
*Steve J. Noll, WA6EJO
http://www.qrz.com/db/WA6EJO
http://www.linkedin.com/in/stevejnoll*


On 11/5/2013 9:16 AM, Zack Widup wrote:
> I'm more interested in "setups for balls-out record setting distances."
> :-)
>
> I wish I could remember the part number of the diode that someone
> recommended as one of the best. I do remember it wasn't easily available in
> the USA. Also, is there something fairly new that would do well?
>
> I have a few of the Golden Dragon 1-watt red LED's. They are extremely
> bright. I recall seeing a mod that can be done by cutting through the case
> and cutting one lead internally to make them useful as detectors. I haven't
> tried this yet.
>
> 73, Zack W9SZ
>
>
> On Tue, Nov 5, 2013 at 10:50 AM, Steve J. Noll<sjnoll at ix.netcom.com>  wrote:
>
>> On 11/1/2013 10:39 AM, Zack Widup wrote:
>>
>>> Once upon a time, probably several years ago, there was some discussion
>>> about what detector diode device was best for laser reception. I remember
>>> there was one device in particular that was recommended and that it was
>>> somewhat difficult to come by.
>>>
>>> Things may have changed since then with advancing technology. Are there
>>> any
>>> suggestions?
>>>
>>> 73, Zack W9SZ
>>>
>>
>> I'd like to see that discussion too!
>>
>> I believe one may want to look at it two ways - setups "capable of
>> communications at a range of at least 1 km." or setups for balls-out record
>> setting distances.
>>
>> For the latter, really can't beat a photomultiplier tube. Next would be an
>> avalanche photodiode.
>> I just retired from being senior test engineer at Advanced Photonix where
>> we made large area Silicon APDs, 5mm to 16mm dia, the biggest in the
>> industry.
>> Unfortunately, they're really expensive, even as surplus, as they're not
>> easy to make. Also require ~1800V. As the operating point is temperature
>> sensitive they're usually TE cooled.
>> These were supposed to be a PMT-killer, they haven't been.  They're the
>> sensors in the Optos scanners at your better-equipped eye doctor.
>>
>> Then there's small area APDs. We made those for long-range barcode
>> scanners. 100V to 200V.
>> I see on eBay right now First Sensor (formerly Pacific Silicon Sensor)
>> AD500 small area APDs for $16 from China. How someone can sell these for $16
>> when they're $135 from Mouser is a mystery, one hopes they're not rejects.
>> Their spectral response curve is not great. About 155V bias requirement
>> which is also temperature dependent.
>> The biggest disadvantage is the tiny active area (500 um.) Can you get
>> most of your receive signal on that 20 mil spot?
>> If not then I'd go with a regular silicon photodiode which you can get
>> with much larger active areas. And they're cheap.
>>
>> 73,
>> *Steve J. Noll, WA6EJO
>> http://www.qrz.com/db/WA6EJO
>> http://www.linkedin.com/in/stevejnoll
>> *
>> ______________________________________________________________
>> Laser mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/laser
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Laser at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Laser mailing list
> Home: http://mailman.qth.net/mailman/listinfo/laser
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Laser at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>