Optical Fiber Ampler (OFA for short) refers to a new type of all-optical amplifier used in optical fiber communication lines to realize signal amplification. According to its position and function in the optical fiber line, it is generally divided into three types: relay amplification, pre-amplification and power amplification. Compared with the traditional semiconductor laser amplifier (SOA), OFA does not need to go through complex processes such as photoelectric conversion, electro-optical conversion and signal regeneration, and can directly amplify the signal all-optically. It has good "transparency" and is especially suitable for long distances. Relay amplification for optical communication. It can be said that OFA has laid a technical foundation for the realization of all-optical communication.