IEC 61290-1-1:2020 applies to all commercially available optical amplifiers (OAs) and optically amplified modules. It applies to OAs using optical fibre amplifiers (OFAs) based on either rare-earth doped fibres or on the Raman effect, semiconductor OAs (SOAs) and planar optical waveguide amplifiers (POWAs). The object of this document is to establish uniform requirements for accurate and reliable measurements, by means of the optical spectrum analyzer (OSA) test method, of the following OA parameters, as defined in IEC 61291-1: - nominal output signal power; - gain; - polarization-dependent gain (PDG); - maximum output signal power; - maximum total output power. In addition, this document provides the test method of: - gain ripple (for SOAs). NOTE All numerical values followed by (‡) are suggested values for which the measurement is assured. The object of this document is specifically directed to single-channel amplifiers. Test methods for multichannel amplifiers are standardized in IEC 61290-10 (all parts). This fourth edition cancels and replaces the third edition published in 2015 and constitutes a technical revision. This edition includes the following significant technical change with respect to the previous edition: addition of techniques to test gain ripple of SOAs.