It has three pins; two for connecting 5V and GND, and one for turning the laser on and off. 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 someone can tell me how to wire this sucker? Also, that. ROHM refers to the pins of a three-pin package as pins 1, 2 and 3, clockwise when viewed from the top of the package (the side where the laser beam is emitted). [An example of a 3-pin package. ]. Googling "common pin" indicates it has some relation to ground, but I didn't find a definitive answer. I suspect that the "2" pin on the laser diode is meant to go to ground, since pin 1 is for the photo-diode and pin 3 is for the cathode, but the datasheet doesn't explicitly mention this. LIV and spectral measurements can be downloaded by clicking the red icon corresponding to each serial number. TO-packaged laser diodes are available in standard Ø3. If you buy a single laser diode as a standalone component, you need to set up a driver circuit that controls the current through the. A laser diode (LD, also injection laser diode or ILD or semiconductor laser or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction. : 3 Driven by voltage, the doped.