Three pins of laser diode

The laser diode has three pins: LD transmitting terminal, PD receiving terminal, LD-N common terminal

1. Distinguish between LD and PD. Use the R×1k block of the multimeter to measure the resistance between the three pins of the laser diode. Once the resistance between the two pins is about a few thousand ohms, the end of the black meter pen is connected to PD anode terminal, the pin connected to the red test lead is the common terminal, and the remaining pin is the LD cathode terminal, which distinguishes the PD part (the bc part in the figure) and the LD part (the ab part in the figure) .

2. Detect the PD part. The PD part of the laser diode is essentially a photodiode. The detection method with a multimeter is as follows: use R×1k to measure its resistance. If the forward resistance is several thousand ohms and the reverse resistance is infinite, it preliminarily shows that the PD part is good ; If the forward resistance is 0 or infinite, it indicates that the PD part is broken. If the reverse resistance is not infinite, it means that the PD part has reversed leakage, and the quality of the tube has deteriorated.

3. Detect the LD part. Use the R×1k block of a multimeter to measure the forward resistance of the LD part, that is, connect the black test lead to the common terminal b and the red test lead to pin a. The forward resistance should be between 10kΩ and 30kΩ, and the reverse resistance should be infinite. If the measured forward resistance value is greater than 55kΩ, and the reverse resistance value is below 100kΩ, it indicates that the LD part has been severely aged and the use effect will be worse.