This part of IEC 1300 describes the procedure to measure the far-end crosstalk of light between channels of a multiport MxN or 1xN fibre optic passive components (switch, WDM or, in particular cases, fan-out). The far-end crosstalk is defined as the ratio of the optical power that goes out from a given output port to an optical power that goes out from another output port, nominally isolated from the previous one.