IEC 61290-1-3:2021 is available as IEC 61290-1-3:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61290-1-3:2021 applies to all commercially available optical amplifiers (OA) and optically amplified subsystems. It applies to OA using optically pumped fibres (OFA based on either rare-earth doped fibres or on the Raman effect), semiconductors (SOA), and waveguides (POWA). NOTE 1 The applicability of the test methods described in this document to distributed Raman amplifiers is for further study. The object of this document is to establish uniform requirements for accurate and reliable measurements, by means of the optical power meter test method, of the following OA parameters, as defined in IEC 61291-1: - nominal output signal power; - gain; - polarization-dependent gain; - maximum output signal power; - maximum total output power. NOTE 2 All numerical values followed by (‡) are suggested values for which the measurement is assured. Other values can be acceptable upon verification. This document applies to single-channel amplifiers. For multichannel amplifiers, IEC 61290-10 (all parts) applies. This fourth edition cancels and replaces the third edition published in 2015. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - harmonization with IEC 61290-1-1; - use of the term "measurement uncertainty" instead of "measurement accuracy".