Scope and object This part of IEC 61292@ which is a technical report@ applies to optical amplifiers (OAs) using active fibres and waveguides@ containing rare-earth dopants@ currently commercially available. It provides guidance on crosstalk caused by the four-wave mixing (FWM) effect. The object of this technical report is to provide introductory information for understanding of the crosstalk issue raised by the FWM effect. This report also presents a measurement method in Annex A.