ABSTRACT
An optical amplifier (OA) is a device that amplifies the optical signal directly, without converting it to an electrical signal and then to an optical signal again. OAs is used for amplifying a weak optical signal in order to increase the distance the signal can be transmitted down the transmission lines. This chapter presents the fundamentals of OAs, their characteristics, and classifications of common ones, describes their applications. The three basic technologies are: Erbium-doped fibre optical amplifiers (EDFA), semiconductor optical amplifiers, and Raman optical amplifiers. EDFAs combined with wavelength division multiplexing technology are widely used in long-distance optical communications, networks, and signal modulation. Optical amplifiers are used to boost signals transmitted over long distances in network systems. Optical amplifiers are used to boost signals in local area networks, when placed in sub centres within the transmission lines and branches. This type of arrangement also enables optical amplifiers to have the characteristics suitable for analogue transmission.
