IEC 61290-3-3:2013 applies to all commercially available single channel optical amplifiers (OAs), including OAs using optically pumped fibres (OFAs) based on either rare-earth doped fibres or on the Raman effect, semiconductor optical amplifier modules (SOA modules) and planar optical waveguide amplifiers (POWAs). More specifically, it applies to single channel OAs placed before optical receivers, where there are no optical bandpass filtering elements placed between the OA and the receiver. The object of this part of IEC 61290-3 is to establish uniform requirements for accurate and reliable measurement of the ratio of the signal output power to the total ASE power generated by the OA in the optical bandwidth of the receiver. This quantity is a measure of the spontaneous-spontaneous beat noise at the receiver, and is correlated to the spontaneous-spontaneous noise factor of the OA, Fsp-sp, as defined in IEC 61290-3 and IEC 61291-1. Keywords: single channel optical amplifiers (OAs), semiconductor optical amplifier modules (SOA modules), planar optical waveguide amplifiers (POWAs), measurement of the ratio of the signal output power to the total ASE power generated by the OA in the optical bandwidth of the receiver