IEC 61280-1-3:2021 is available as IEC 61280-1-3:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61280-1-3:2021 provides definitions and measurement procedures for several wavelength and spectral width properties of an optical spectrum associated with a fibre optic communication subsystem, an optical transmitter, or other light sources used in the operation or test of communication subsystems. This document also provides definitions and measurement procedures for side-mode suppression ratio and signal-to-source spontaneous emission ratio. The measurement is done for the purpose of system construction and/or maintenance. In the case of communication subsystem signals, the optical transmitter is typically under modulation. NOTE Different properties can be appropriate to different spectral types, such as continuous spectra characteristics of light-emitting diodes (LEDs), as well as multilongitudinal-mode (MLM), multitransverse-mode (MTM) and single-longitudinal mode (SLM) spectra, which are characteristic of laser diodes (LDs). This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- addition of measurement of signal-to-source spontaneous emission ratio in 8.9;
- change of document title to reflect the additional measurement;
- additional information on the resolution bandwidth used in the measurement of the side-mode suppression ratio in 8.8;
- use of a calibrated optical wavelength meter for accurate wavelength measurements of single-longitudinal mode lasers.