This part of IEC 61300-3 describes the various methods available to measure the wavelength dependence of attenuation A(?) and return loss RL(? ), of single-mode passive optical components (POC) used in fibre-optic (FO) telecommunications. It is not, however, applicable to dense wavelength division multiplexing (DWDM) devices. Measurement methods of wavelength dependence of attenuation of DWDM devices are described in IEC 61300-3-29. Definition of WDM device types is given in IEC 62074-1. Three measurement cases are herein considered: - Measurement of A(? ) only; - Measurement of RL(? ) only; - Measurement of A(? ) and RL(? ) at the same time. These measurements may be performed in one direction (unidirectional) or bi-directionally.