Laser diodes can be single emitters, meaning that it emits laser light from a single active region, as shown in Figure 1a. Laser diodes are electrically pumped semiconductor lasers in which the gain is generated by an electric current flowing through a p–n junction or (more frequently) a p–i–n structure. This junction is known as a p-n junction. These semiconductors are incredibly small, made of very thin slices of semiconducting material, and are very. A laser diode (or diode laser) is a semiconductor device that undergoes stimulating emission to emit coherent light. They consist of a p-n semiconductor junction, with a forward bias voltage applied. The optical power value, Po, is the most basic characteristic of a laser diode.