This part of IEC 61300 identifies two basic measurement methods for characterizing the spectral transfer functions of DWDM devices. The transfer functions are the functions of transmittance dependent of wavelengths. In this standard, optical attenuations are also used. NOTE In this standard, transfer functions are expressed by T(λ) and optical attenuations are expressed by A(λ). The transfer functions can be used to produce measurements of insertion loss (IL), polarization dependent loss (PDL), isolation, centre wavelength, bandwidth (BW) and other optical performances.