Semiconductor laser, also known as laser diode, is the use of semiconductor materials as a working medium to produce a class of laser excited emission. Commonly used materials are gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), zinc sulfide (ZnS). Excitation mode has three forms of electric injection, electron beam excitation and optical pumping excitation. According to the different laser media and working principle, semiconductor lasers can be divided into the following categories: 1. Laser diode: the working principle of the laser diode is that the current is injected into the PN junction, and the electrons and holes are compounded in the junction region, releasing laser photons. Since the junction region of the PN junction is very small, a very dense laser beam can be produced. The wavelength of a laser diode is usually between 800nm and 980nm, which makes it suitable for applications such as fibre optic communications.2. Vertical Cavity Surface Emitting Laser (VCSEL): A vertical cavity surface emitting laser (VCSEL) is a type of laser that is fabricated on a semiconductor chip. Its laser output is perpendicular to the surface of the chip, which enables efficient coupling into optical fibres or other optical components, and therefore has a wide range of applications in the fields of optical communications, optical storage, optical printing, etc. 3. Boundary Emitting Laser (EEL) Boundary Emitting Laser (EEL) is a kind of semiconductor laser that emits lasers at the boundaries of PN junctions. Its structure is similar to a laser diode, but on the side of the PN junction to increase a layer of mirrors, so that the laser oscillates at the boundary of the PN junction, the advantages of the EEL is a high output power, wavelength adjustable, simple structure, etc. 4. quantum well lasers: quantum well lasers are a kind of semiconductor lasers that use the pure effect of electron beams in the structure of quantum wells to generate lasers. Quantum well lasers have the advantages of adjustable wavelength, high output power, low illumination, etc. They are suitable for fibre optic communication, medical treatment and spectral analysis, etc. Vertical Epitaxial Laser: Vertical Epitaxial Laser (VLEC) is a kind of semiconductor laser manufactured by epitaxial growth technology. high-speed optical communication, optical storage and optical printing and other fields.

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