Laser tube type: Common type 3 semiconductor laser tubes on the market. VCSEL semiconductor laser tubes generally do not undergo fiber coupling. They are the type of semiconductor laser tubes commonly found in large diffusion sensing applications, such as computer mouse devices or smartphone 3D sensing facial recognition. DFB and FP are edge emitters, usually fiber coupled.

a. FP (Fabry-Perot) Fabry-Perot semiconductor laser tube.
FP laser, the most common and common semiconductor laser, is a semiconductor light-emitting device that uses the FP cavity as the resonant cavity and emits multi-longitudinal mode coherent light. The technology is very mature and widely used. However, the spectral characteristics of FP are not good, and there are problems with multiple side modes and dispersion. Therefore, it can only be used for medium-low speed (speed below 1-2G) and short-distance applications (less than 20 kilometers).
In order to reduce the emission bandwidth and improve the overall stability of the semiconductor laser tube, semiconductor laser tube manufacturers often add fiber Bragg gratings within the output fiber. Bragg gratings add a few percent reflectivity to a semiconductor laser tube at a very precise wavelength. This will reduce the overall emission bandwidth of the semiconductor laser tube. The emission bandwidth without a Bragg grating is typically 3-5nm, while with a Bragg grating it is much narrower (<0.1nm). The wavelength spectrum temperature tuning coefficient without a Bragg grating is typically 0.35 nm/°C, whereas with a Bragg grating this value is much smaller.