This part of 61290 applies to commercially available optical amplifiers (OAs) such as optical fibre amplifiers (OFAs), semiconductor optical amplifiers (SOAs) and planar waveguide amplifiers (PWOAs) as classified in IEC 61292-3. The object of this standard 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: a) signal-spontaneous noise figure; b) forward amplified spontaneous emission (ASE) power level. The methods described in this part of IEC 61290 apply to single-channel stimulus only. Two alternatives for determining the signal-spontaneous beat noise are possible, namely the ASE direct interpolation technique (DI) and the polarization nulling with interpolation technique (PN). The accuracy of the DI technique will suffer when the slope of the OA spectral ASE curve has large wavelength dependence, as in the case of an OA with an internal narrowband ASE suppressing filter. The accuracy of the DI technique degrades at high input power level due to the spontaneous emission from the laser source(s). Annex A provides guidance on the limits of this technique for high input power.