A collimator is an optical component used for input and output in fiber optic communication optical devices. Its structure is simple - the divergent light emitted from the fiber is transformed into parallel light (Gaussian beam) through a convex lens in front of it. Its function is to couple light into the desired device with maximum efficiency or to facilitate the reception of light signals with maximum efficiency. So it has an important parameter: insertion loss, and the process technology can reach below 0.15dB.