Problem with Saturating Photodiode
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Posted by Jim Thompson on December 8, 2006, 10:53 am
Please log in for more thread options I just ran onto a situation where a modulated laser impinging upon a photodiode had such a high light level that the photodiode was "saturated"... no more available carriers. Thus "clipping" of the modulation was occurring in the photodiode itself, creating harmonics. And lowering the DC bias on the laser raised the AC signal level... really strange lab results to ponder when you're tired ;-) Any ideas how one might *model* the photodiode in Spice? ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by John Larkin on December 8, 2006, 11:10 am
Please log in for more thread options On Fri, 08 Dec 2006 08:53:57 -0700, Jim Thompson How can it run out of carriers? Photons make h-e pairs, and more photons should make more, right? Does high pair density increase recombination before the charges can be collected? Is it possible that the photocurrent is limited by ohmic effects? The DC effect does need pondering. One of the makers of GaAs photodiodes told us that their devices would limit above about a milliwatt optical input, so we got access to a multi-watt pulsed fiber source, and it turns out they were wrong. John | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Jim Thompson on December 8, 2006, 11:23 am
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On Fri, 08 Dec 2006 08:10:40 -0800, John Larkin >On Fri, 08 Dec 2006 08:53:57 -0700, Jim Thompson
> >>I just ran onto a situation where a modulated laser impinging upon a
>>photodiode had such a high light level that the photodiode was >>"saturated"... no more available carriers. >> >>Thus "clipping" of the modulation was occurring in the photodiode >>itself, creating harmonics. >> >>And lowering the DC bias on the laser raised the AC signal level... >>really strange lab results to ponder when you're tired ;-) >> >>Any ideas how one might *model* the photodiode in Spice? >> >> ...Jim Thompson >
>How can it run out of carriers? Photons make h-e pairs, and more >photons should make more, right? Hell! I don't know, I'm a circuit guy, not a physicist ;-) >Does high pair density increase
>recombination before the charges can be collected? Is it possible that >the photocurrent is limited by ohmic effects? The DC effect does need >pondering. 10V reverse bias. >
>One of the makers of GaAs photodiodes told us that their devices would >limit above about a milliwatt optical input, so we got access to a >multi-watt pulsed fiber source, and it turns out they were wrong. > >John Problem cured by going to a larger photodiode. This data is all remote provided... lab in Atlanta, me in Phoenix. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Joerg on December 8, 2006, 11:40 am
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Jim Thompson wrote: > On Fri, 08 Dec 2006 08:10:40 -0800, John Larkin
> > >>On Fri, 08 Dec 2006 08:53:57 -0700, Jim Thompson
>> >> >>>I just ran onto a situation where a modulated laser impinging upon a
>>>photodiode had such a high light level that the photodiode was >>>"saturated"... no more available carriers. >>> >>>Thus "clipping" of the modulation was occurring in the photodiode >>>itself, creating harmonics. >>> >>>And lowering the DC bias on the laser raised the AC signal level... >>>really strange lab results to ponder when you're tired ;-) >>> >>>Any ideas how one might *model* the photodiode in Spice? >>> >>> ...Jim Thompson >>
>>How can it run out of carriers? Photons make h-e pairs, and more >>photons should make more, right? >
> > Hell! I don't know, I'm a circuit guy, not a physicist ;-) > > >>Does high pair density increase
>>recombination before the charges can be collected? Is it possible that >>the photocurrent is limited by ohmic effects? The DC effect does need >>pondering. >
> > 10V reverse bias. > That can reduce your selection. Some are spec'd at 5V max, so I went from 12V to 5V. >
>>One of the makers of GaAs photodiodes told us that their devices would
>>limit above about a milliwatt optical input, so we got access to a >>multi-watt pulsed fiber source, and it turns out they were wrong. >> >>John >
> > Problem cured by going to a larger photodiode. > > This data is all remote provided... lab in Atlanta, me in Phoenix. > Paper said it was 22F at night. Ask them to scrape the ice off the PD's front and measure again :-))) -- Regards, Joerg http://www.analogconsultants.com | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Joerg on December 8, 2006, 11:34 am
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John Larkin wrote: > On Fri, 08 Dec 2006 08:53:57 -0700, Jim Thompson
> > >>I just ran onto a situation where a modulated laser impinging upon a
>>photodiode had such a high light level that the photodiode was >>"saturated"... no more available carriers. >> >>Thus "clipping" of the modulation was occurring in the photodiode >>itself, creating harmonics. >> >>And lowering the DC bias on the laser raised the AC signal level... >>really strange lab results to ponder when you're tired ;-) >> >>Any ideas how one might *model* the photodiode in Spice? >> >> ...Jim Thompson >
> > How can it run out of carriers? Photons make h-e pairs, and more > photons should make more, right? Does high pair density increase > recombination before the charges can be collected? Is it possible that > the photocurrent is limited by ohmic effects? The DC effect does need > pondering. > > One of the makers of GaAs photodiodes told us that their devices would > limit above about a milliwatt optical input, so we got access to a > multi-watt pulsed fiber source, and it turns out they were wrong. > I was told that besides non-linearity there comes a point beyond which there would be irreversable damage. Also, the datasheet for the Sumitomo diode I am using here states 2mA Ir as the abs max limit. BTW I found this to be a pretty good paper: http://sales.hamamatsu.com/assets/applications/SSD/photodiode_technical_information.pdf -- Regards, Joerg http://www.analogconsultants.com | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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>photodiode had such a high light level that the photodiode was
>"saturated"... no more available carriers.
>
>Thus "clipping" of the modulation was occurring in the photodiode
>itself, creating harmonics.
>
>And lowering the DC bias on the laser raised the AC signal level...
>really strange lab results to ponder when you're tired ;-)
>
>Any ideas how one might *model* the photodiode in Spice?
>
> ...Jim Thompson