IEC 61280-1-1:2013 applies to fibre optic general communication subsystems. The object of this part is to measure the optical power coupled from the output of a transmitter under test into single-mode optical fibre cable containing dispersion-unshifted fibre or dispersion-shifted fibre. This second edition cancels and replaces the first edition published in 1998. This second edition constitutes a technical revision. The significant technical change with respect to the previous edition is the inclusion of Annex A on how to account for uncertainties. There are editorial corrections throughout the document and updates to references. Keywords: measure the optical power coupled from the output of a transmitter under test into single-mode optical fibre cable containing dispersion-unshifted fibre or dispersion-shifted fibre