The couplers are components where two fibers are fused together, allowing the injection of signals from two different fibers into the core of a single fiber. For example, this allows for injecting pump light into the fiber core that is propagating a signal towards an amplification medium.
FBGs are used to stabilize the wavelength of pumps or sources, monitor the signal quality of optical transmission lines in data transmission applications or as reflectors in laser resonators. Additionally, they can be designed to be thermally stable, maintaining their properties even where there are temperature variations.
Dispersion compensators are used to compensate for the chromatic dispersion effect that occurs between two fiber amplifiers when the signal is transmitted over a long distance, as is often the case in applications such as FTTH (Fiber to the home).