This European Telecommunication Standard (ETS) applies to Optical Amplifier (OA) devices and sub-systems to be used in transmission networks. It covers both Optical Fibre Amplifiers (OFAs) and Semiconductor Optical Amplifiers (SOAs). The object of this ETS is to specify those generic characteristics relevant for the use of OA devices (as power amplifiers, pre-amplifiers or line amplifiers) and OA sub-systems (as optically amplified transmitters or optically amplified receivers), primarily for applications in digital transmission.