Possibility of laser diode damage due to fast modulation

[weartronics]

I want to digitally modulate a laser diode between zero power and full power at a frequency of 100 kHz. I realise that the thermal and optical stability is probably better if I switch between the threshold current and the maximum current, but for simplicity I would prefer to switch between zero current and the maximum current. Will the laser diode lifetime be shorter because I am switching between zero current and the maximum current, instead of using the threshold current?

[ElektroFreak]

The general consensus is that it is safe as long as the maximum current never exceeds the diode's maximum rated current. I haven't heard anything about shortening the diode's life by modulating from zero to full power.

[tocket]

Indeed, as long as the transient (which is likely larger when you modulate from full off to full on) doesn't cause the maximum current to be exceeded it should be OK. Easy to check with an oscilloscope though.

[weartronics]

Thanks for the info, this is good news!

[allthatwhichis]

Well... and this is the dumbass speaking, bit I seem to recall everyone running their reds and blu-rays with a soft start, always keeping it just above threshold, for some reason to do with health of the diode... Even the Kvant does it with the red diodes. Not the 445nm blue, that I can see, for some reason.

Someone... Mo... Mike... help me out here.

[FourDee]

Yes, that's what I've read. No damage when you don't exceed max CW power AND you stay above threshold ...

Don't remeber what document that was in though ...

[ElektroFreak]

I don't know for absolutely certain, but I think that the reason for that is for power stability rather than damage prevention, but I could be mistaken..

[MechEng3]

I would abstain from modulation from 0 volts/current on any diode....unless it is a very cheap experiment. Diodes don't like the shock wave of heat from the inrush of current....it tends to blow the facet off the die....no more laser. I may stand correctable here....but I would opt to run it just above threshold to save the diode. Even if it is the faintest light from it...it is at least conducting current and somewhat in the "running" mode of ops. Then again.......just from my own testing....need more info on the diode.

[heroic]

DVD burners keep the laser just above threshold not because of any lifespan concern but for two other reasons:

- this is how they sense and track the stamped groove that allows them to write the data in the right place

- laser diodes modulate much faster if they're kept in conduction (since, when the diode is conducting, there's no depletion zone and therefore no junction capacitance).

The temperature thing is a red herring with low power diodes like DVD burners and such. Threshold on these diodes is at such low powers that the facets are at room temperature (I've checked this with an IR microprobe- great toys we had at TI...) I'd believe it if someone told me that whacking great 808 diode bars and that kind of thing are different though- threshold may be at a couple watts of electrical power in those lasers, which would be enough to warm the die appreciably.