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Old 01-03-2010, 08:31 PM #1
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Default Photodiode feedback circuitry

Hi, Great Forums!

Im trying to get a general idea of how the photodiode in laser diodes can be used to regulate the current to the laser diode. What kind of feedback circuitry could be used for this? i understand that the voltage drop across the photodiode is proportional to optical output power of the laser diode but i am having trouble figuring out how to use this to any useful effect.

Any help or thoughts would be greatly appreciated

thanks


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Old 01-03-2010, 08:40 PM #2
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Default Re: Photodiode feedback circuitry

The drivers using the photodiode usually have an op amp as the regulator. They use one of the inputs as the feedback control from the photodiode. Most of the new high power diodes we are using dont have that feature anymore.

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Old 01-04-2010, 04:46 PM #3
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Default Re: Photodiode feedback circuitry

So LD's like the PHR 803T wont have the photodiode built in?
How in this case is the optical output power stabilized, is this done solely through stable current and temperature control?
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Old 01-04-2010, 05:21 PM #4
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Default Re: Photodiode feedback circuitry

Nah, most of the burner sleds have external photodiodes that take part of the beam (from the cube or from a beamsplitter) and uses them for the diode feedback ..... there you also see some trimmers, usually connected to the photodiode, for the different diodes reading circuits .....
Just as example, in the PHR sled, it's here .....



And, before you ask, yes, i already tried to use them for make an LPM, but they are too much small ..... it's a pity, cause they have a decent sensitivity from IR to UV, but with a 1 to 1.5mm surface, nothing to do .....

Edit: maybe using a trick ..... putting a sanded glass of a certain surface in front as diffuser, and a focusing lens that focuse the image of the glass on the diode ..... but i see it critical, anyway .....
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Photodiode feedback circuitry-phrphotodiode.jpg  
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