Sonsivri

Hi dear, I'm doing a project that use laser diodes, I use laser built-in photodiode in feedback for current regulation, but i need to calibrete a trimmer on feedback to have right optical power.
Someone knows how to measure optical mw power? a cheaper instrument?
max power 10mW, min power 0.1mw

Thanks
Max

Hi,
I think that the bare minimum is to post here either the PN for the laser diode you are going to use or even better the datasheet.
Afaik, for the embedded photodiode you also need a constant current source (the resistor + pot combo you used may count as a very basic CCS but it may be better to use another solution). Also you can use a simple uC like PIC 10F322 that has an ADC and simplify the PCB. This way, you can create a calibration curve in the uC when measuring the photodiode voltage drop across a resistor (laser power vs photodiode current curve may not be linear due to overall heating done by the laser diode).

LE:
Regarding the laser power meter, depending on the wavelength of the laser diode you may use something like this maybe with some adaptation:
https://www.aliexpress.com/item/1005001453763968.html?spm=a2g0o.productlist.0.0.518d79b9FslWjp&algo_pvid=7e8b4e91-1453-4fd2-b399-0692e4b3a77d&algo_expid=7e8b4e91-1453-4fd2-b399-0692e4b3a77d-22&btsid=0b0a01f816149624801342633e33fb&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

This one has a large measuring band but is costly though:
https://www.aliexpress.com/item/1005002023431151.html?spm=a2g0o.productlist.0.0.518d79b9FslWjp&algo_pvid=7e8b4e91-1453-4fd2-b399-0692e4b3a77d&algo_expid=7e8b4e91-1453-4fd2-b399-0692e4b3a77d-20&btsid=0b0a01f816149624801342633e33fb&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

Hi, Mars thanks for your reply, yes this is first step, but at the end it will interfaced with uC but for output power measurement, for regulation I think i remain into analog application.
I don't have much experience on photodiodes, just as receiver, but from my knowledge, the photodiede behaves as current generator in function of photones which hit the valence band generating a passage of charges.
From laser datasheet seems that the internal photodiode is stable and temperature autocompensated because is done on the same layer of laser with a more than acceptable linearity, today to calibrate I use an empirical system, I take an current source (with lm334 or REF200) connect to feedback resistor and I check voltage at testing current and check graphic, it's not very accurate, but in this way I don't burn laser, circuit works fine, but i don't know true power, just calculaterd...

Laser are some types, but predominantly ADL.63054L or HL6312: wavelength 635nm and 5mw max power.

Here from HL6312 linearity of photodiede and temperature influence:

If you want accuracy, then it is this.

https://en.wikipedia.org/wiki/Integrating_sphere

Why do you need specific power levels and how accurate does it HAVE to be?

To do some optical experiment measure laser output (source) and then measure beam power after lens and filters pass through, but instrument are very expensive for me
Accuracy already 0,1mW is ok, best 0,01mW is best

Dear M@X77, are you from Italy? (just asking because the title of the schematic). Are you studying, or working with this? I think that the UNI-T option is not so expensive (except if you´re a student and will use this only once), and most being in Italy, where you can buy this freely.
Anyways, the first option seems to be good enough, but try to get a complete specifications list before buy.
Optikon, your suggestion is the best accurate one, but how to get acces to this system, outside of an university? Or maybe a specialized enterprise, where the test will be more expensive than 10 UNI-T meters? Plus, in a university, this equipment usually is under domain of a crazy electric engineer who "plans how to domain the world"... LOL. Anyway, is the most accurate and precise  method.
Choice will depend on the precision that M@X77 requires.
Regards.

You sound confused, which makes me confused

In your original posting you talked about maintaining a power output. Now you are talking about measuring it.

That is two separate problems.

I think that he refers to measuring the original power to calibrate the receptor on this base. Correct me if I"m wrong.
Regards

Yes, you are right, in first part is the source circuit to explain witch trimmer i need to set and this depend directly from PD, then that the project are to laser and optical experience...

Posted on: March 08, 2021, 12:22:11 00:22 - Automerged

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Yes I from Italy, and you?
I work, but this is for hobby and my money resources for electronics projects and studies are drastically decrease with family growing...
Pandemic period has decreased more the limitated resources...
Univerisity methode is very interesting, but crazy electric engineer or not the access is denied for me....
For me precision is 0.1mW or greatfully 0.01mW
The UT385 is really interesting and I think could be satisfy my necessity, but for me now is economically inaccessible...
And Italian prices are more expensive of 2 or 3 times the aliexpress price... but 100€ in china is about 150-170€ with vat and duty tax.
I'm thinking to stop for the moment experiments I'll wait a best time...

Nice. I´m from Argentina, italiani all estero... :-)
I undestand you more than you think.. I had to wait too for instruments... The best way is to find a commercial application for some of your designs, and include in this the meters you need for future works.... (kinda cheat, but not really). I did in that way, and things went so and so good. Of course, some sacrifices in the middle, but you finally get what you need.
Just be patient.

you are right, good way and be patient, very patient

Good evening M@X77. How is your project going? did you get an adequate instrument, or hired someone to evaluate this? Let me know.
Regards,

hi Poty, the project was in the drawer, is still wait more economical rss...
thx
Max