IEC 61291-1:2012 applies to all commercially available optical amplifiers (OAs) and optically amplified assemblies. It applies to OAs using optically pumped fibres (OFAs based either on rare-earth doped fibres or on the Raman effect), semiconductors (SOAs), and waveguides (POWAs). This third edition cancels and replaces the second edition published in 2006. It is a technical revision that includes the following significant changes: the definitions related to transient behaviour have been extensively updated with terms from the 61290-4 series and the definition for gain ripple has been added.