This part of IEC 61753 contains the minimum initial test and measurement requirements and severities which a fibre optic middle-scale 1 ?? N (16 ?? ??4) DWDM (dense wavelength division multiplexing) device with channel spacing of 50 GHz@ 100 GHz or 200 GHz needs to satisfy in order to be categorized as meeting the requirements of category C ?C Controlled environment. The requirements are given for the DWDM devices with Gaussian passband profile and flat-top passband profile. The requirements cover devices with single-mode nonconnectorized pigtails and no circuit board.