Why do laser diodes have 3 pins
The active region of the laser diode is in the intrinsic (I) region, and the carriers (electrons and holes) are pumped into that region from the N and P regions respectively. It has three pins; two for connecting 5V and GND, and one for turning the laser on and off. Can anyone tell my why this laser diode has three wires? To power up the laser I'm guessing I need to put some VDC across pins 1 and 2? But what's the other diode on pins 2 and 3 for? I guess the datasheet does actually explain this somewhere but it's a tad arcane for me and I'd appreciate it if. I don't have a solid answer as to 'why' they do this, but will share a few possibilities for debate: Far too small for practical heatsinking in my opinion. A packaged laser diode shown with a penny for scale: a 488 nm InGaN green-blue laser, which became widely available in mid-2018.
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