Effect of polarisation-dependent loss on the performance accuracy of a ratiometric wavelength measurement system

The polarisation-dependent loss (PDL) of a ratiometric wavelength measurement system and its influence on system´s accuracy are investigated theoretically and experimentally. The PDL of a ratiometric system and the corresponding power ratio fluctuation is modelled, from which the accuracy of the measured wavelength can be estimated. An all-fibre wavelength measurement system is built to allow comparison of modelled and actual results. The measured ratio variation lies within the estimated limits. The measured wavelength error reaches about 1.41 plusmn 0.09 nm at 1550 nm in the demonstrated example (with an edge filter of average slope 0.22 dB/nm), which indicates the significant influence of PDL on the accuracy of a ratiometric wavelength measurement system.