This part of IEC 61290 applies to all commercially available optical amplifiers (OAs) including optical fibre amplifiers (OFAs) using active fibres and semiconductor optical amplifiers (SOAs) using semiconductor gain media. Polarization mode dispersion (PMD) causes an optical pulse to spread in the time domain. This dispersion could impair the performance of a telecommunications system. The effect can be related to differential group velocity and corresponding arrival times of different polarization components of the signal. For a narrowband source, the effect can be related to a differential group delay (DGD) between pairs of orthogonally polarized principal states of polarization (PSP). This test method describes a procedure for measuring the PMD of OAs. The measurement result is obtained from the measurement of the normalised Stokes parameters at two closely spaced wavelengths. The mathematical basis together with an example of calculation for the Poincaré sphere analysis (PSA) method to calculate PMD is provided in the technical report IEC 61292-5. The method described herein has been shown to be immune to polarization-dependent gain (PDG) and polarization-dependent loss (PDL) up to approximately 1 dB [‡]. Although the PSA, in practice, is applicable to unpumped (that is, unpowered) OAs, the PSA technique in this standard applies to pumped (that is, powered) OAs only. NOTE All numerical values followed by (‡) are suggested values for which the measurement is assured. Other values may be acceptable but should be verified.