The laser emitted by semiconductor laser is coherent light, and its directivity is much better than that of LED, which greatly improves the coupling efficiency between light source and optical fiber. In order to form a laser in a semiconductor laser, the following three basic conditions are needed: 1, which produces enough inversion distribution of particle number in the active region; 2. Optical resonance mechanism exists, and oscillation is established in the active region; 3. Necessary excitation source or pumping source