Question
I use the WLD3343 in collaboration with the WHY5640 and a Peltier element to keep the laser diode temperature constant. After I set the LD current to 40 mA and start changing the temperature from about 16°C to 50°C the LD current starts to rise to 60 mA.
Does that have to do with the characteristic’s of the LD? I know that some things vary depending on the temperature but then I would expect the WLD3343 to adjust the current. It does keep the current constant very well if the temperature stays constant.
Answer
If you are operating the WLD3343 in Constant Power mode, your scenario makes sense.
Keep in mind that if laser diode drive current is kept constant, output power decreases as laser temperature increases. If you are operating the WLD3343 in constant power mode, it will increase the drive current in order to maintain the same optical output power (or, really, the same photodiode current).
You can verify this is the case by switching the WLD3343 to Constant Current mode and increasing the temperature of the diode. You should see the output power of the laser drop while the drive current remains constant.