This part of IEC 61300 specifies measurement methods to determine the dependence of loss in a single-mode fibre optic device to changes in polarization. This procedure focuses on measurements with a fixed wavelength source; therefore, this procedure is applicable to devices whose properties at a single wavelength can represent those over the broader wavelength band. Typical examples of such devices are single-mode interconnecting devices and passive components, including connectors, splices, branching devices, attenuators, isolators, and switches. The maximum observed variation in transmission loss is referred to as polarization-dependent-loss (PDL). This standard applies to broadband devices and not to narrow-band devices like filters and multiplexers. The reader is referred to IEC 61300-3-29 for such measurements.