New Laser power meter

[andrea87]

I've just got off ebay a photodiode based laser power meter module, pretty simple, power sensor and a precision OpAmp to give a valuable output.



From ebay's auction:

This unit was used to track laser power in an application that used a combiner of 24pcs 1Watt fiber coupled lasers. Photocurrent is linear with laser power. Just change one resistor to adapt range to your laser (evidently within limits) .

- Machined aluminium housing with aluminium sheet cover
- anti-reflection coated optical glass window
- Photodetector with 10x10mm sensitive area in ceramic housing, sensitive spectrum 410-1100nm visible-near-infrared
- easy to track double sided circuit board with photocurrent-to-voltage converter with precision AD738/ OP27 operational amplifier
- 10 Pin standard connector supplies power to the circuit and connects the output signal to the outside world.

Used, new appearance, Photodiode junction tested OK.

Here are some photos of the circuit:



As far as I've understood, I'm going to supply this with something like a dual ±15V supply, shot a laser into the photodiode and I'll get some value out. I don't know how much will be linear, but for about 30€ I have plenty of room to work on.

Looking a bit for its connection, I've found a pinout like this:

1) Sensor Cathode
2) output gnd
3) VCC-
4) NC
5) Output
6) NC
7) VCC+
8) Case GND
9) Analog GND
10) connected to c4/r5... still to understand.

Does anyone have used similar sensors? If I hook a 12+12V supply or such to it, and shot a beam into it's sensor, would I get something out without breaking it all?

 

[Benm]

Is that the only information you got on it?

I think it should be safe to connect the power supply, tie all the grounds together and see what happens. 12V sounds reasonable. I'd connect a scope to the output and see if it does anything when you illuminate the sensor.

Pin 10 could be an enable/disable for an RC network that slows sensor response, though that is just speculation on my part.

 

[andrea87]

yep that's all. I've left an email to the seller, as soon as I'll get some DX lasers I'll try it. at the moment I don't have any coherent light source to shine at it, maybe a concentrated point for some other source... I'll try as soon as I've built the dual supply to power it.

On the other side, I don't really know what to do with the diode cathode... why is it coming on the output connector? maybe to add some offset before placing it to gnd?

 

[Kenom]

This is going to be hard to get workin right without the correction factor for the wavelength. I seriously doubt based on what I'm seeing on the board, that it is built into that board. There is probably a meter base that this connects into. While it's true that sensitive spectrum 410-1100nm visible-near-infrared your still going to need to correction factor.

With a photodiode sensor each light is going to be different. 532nm 1 Mw will show different than a 660nm 1 Mw will. It will be tough but it's doable.

 

[lasersbee]

yep that's all. I've left an email to the seller, as soon as I'll get some DX lasers I'll try it. at the moment I don't have any coherent light source to shine at it, maybe a concentrated point for some other source... I'll try as soon as I've built the dual supply to power it.

On the other side, I don't really know what to do with the diode cathode... why is it coming on the output connector? maybe to add some offset before placing it to gnd?

You can get a reading from a Photo Diode sensor using a standard 100 watt incandescant light bulb

From test we did a while back.... at about 1/4" distance you should be able to read 18mW to 22mW
of photonic output...

Jerry

 

[Benm]

Surely that will work, certainly with a sensor that big. Shining it with a flashlight or something should trigger some response.

Calibration for wavelength will likely be an issue, but then again that could be perormed with reference lasers of common wavelengths. As long as the power-vs-voltage curve is linear or known, you should be able to cook something up.