IEC 62129-3:2019 describes the calibration of optical frequency meters using an optical frequency comb as an internal reference. It is applicable to instruments measuring the optical frequency emitted from sources that are typical for the fibre-optic communications industry. It is assumed that the optical radiation will be coupled to the optical frequency meter by a single-mode optical fibre. This document is part of the IEC 62129 series on the calibration of wavelength/optical frequency measurement instruments. Refer to IEC 621291  for the calibration of optical spectrum analyzers, and refer to IEC 62129-2  for calibration of Michelson interferometer single wavelength meters. This first edition cancels and replaces IEC TS 62129-3, published in 2014. This edition includes the following significant technical changes with respect to the previous edition:
a) text has been added to 5.2.3 about calibration at a second optical frequency;
b) Annex D is now normative;
c) Subclause 4.2 has been improved;
d) measurement method of frequency has been moved to Annex B;
e) example of optical frequency comb has been moved to Annex C;
f) frequency-dependence uncertainty has been moved to Annex D.
Keywords: calibration of optical frequency meters