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Current in LPC-815

J

jbord39

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Hey guys,

I am building a driver now for the LPC-815. My idea is to use two constant sources both drawing current through the laser diode, one at 15mA and one between 400-600mA. The idea is to have the 15mA source constant while turning the 400-600mA source on and off at a constant frequency.

I have heard it is better to modulate a laser diode from high current to very low current, rather than from high current to NO current. Does anyone know if this is true in the case of the LPC-815?

Does anyone have any information regarding what frequency to use, or the levels of current that you can pulse the laser at safely?

I am building the testbench right now, so once I get some numbers to try I will try them and let you all know how it goes.

Thanks for any help,

John
 





Blord

Blord

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I wouldn't go higher than 420mA. That is pretty much the upper limit of the LOC red diode. About the modulation I don't know much about it but I think there isn't a problem switching between 15-400mA or 0-400mA.
 
Coherent Light

Coherent Light

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I 2nd Blord on 420ma I'm currently running some at 400ma & 410ma. I do have a LCC at 445ma which is still doing fine after 2 months.
 
qumefox

qumefox

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I have one running at an estimated 500mA that's still alive after a few months.

I just tested it and it again and it peaked at 331mW on the LPM.
 
qumefox

qumefox

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Not brave. it was an accident.. I had it set for 420mW but probably bumped the pot when I was sealing the module up. and i'm not prying it apart again while it's still working. It was doing about 275mW at 420mA.
 
LtKernelPanic

LtKernelPanic

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I set mine to 200ma IIRC and it comes in at 190mw. That doesn't seem right though. With a flexdrive it should draw pretty much what it's feeding the diode shouldn't it?
 
qumefox

qumefox

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Depends on the input and output voltages. Though no driver is 100% efficient.
 
J

jbord39

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Thanks. I'm not really worried about the drivers efficiency though. Has anyone tried like 600 mA pulsed for maybe 1 ms at some kHz? Or higher?

Also how do you guys measure the power? In a diode P=V*I; and V is Vf = ~3V, so with 500 mA you have 1.5 W.
 
qumefox

qumefox

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The problem with the LOC's isn't a thermal issue. It's the optical power handling capabilities of the facet coatings. Running them pulsed isn't going to sideskirt that.

What what power are you measuring? Driver input and output power can be measured with a DMM and a shunt. Optical output power can only be measured with a LPM.
 
J

jbord39

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I'm looking to push the current by pulsing it very quickly, if that is possible.
 
qumefox

qumefox

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Generally milliwatts or watts being discussed here always refers the optical power output. Conversations dealing with heat dissipation etc are usually clearly obvious as such.

And pulsing only helps if the limitation is due to thermal issues. That's not the case with the LOCs out of the lpc-815. The limitation with them is with, as I said before, the power handling capabilities of the facet coatings on the die. When they are burned off due to to high of a power density in the cavity, it's what's known as LEDing your laser diode.. Without the HR and OC coatings to form a cavity and increase gain, it's basically just an LED..
 
Benm

Benm

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jbord39 said:
I have heard it is better to modulate a laser diode from high current to very low current, rather than from high current to NO current. Does anyone know if this is true in the case of the LPC-815?
Click to expand...

Afaik several people believe this to be true, but i have never seen a single shred of evidence to support it.

But as people stated, there is no point in pulsed operation if your goal is maximum average output power - the power/current slope drops off, so pulsed operation at equal average current will actually result in less power... at least when you want a high average power.
 
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