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±0.09nm at 1550nm in the demonstrated example (with an edge filter of average slope 0.22dB/nm), which indicates the significant influence of PDL on the accuracy of a ratiometric wavelength measurement system.