Analytical tools for the assessment of optical crosstalk in WDM systems

Linear optical crosstalk in wavelength division multiplexed (WDM) systems is investigated in order to develop simple design tools that may be employed by engineers to either readily assess or predict the performance of a WDM system. By approximating the source spectrum as well as the transmission spectra of channel-selecting filtering elements to a Gaussian profile, general analytical relationships between the optical crosstalk the channel width and the channel separation are developed. Such expressions have been derived for systems utilising a demultiplexing device only, those employing both multiplexing and demultiplexing components and LED spectral-sliced systems. It is predicted that as a first approximation, the optical crosstalk will usually be around six times the square of the ratio: channel separation/channel width. Thus, a particular optical crosstalk level may be achieved for any value of the channel separation or channel width so long as their ratio (which is introduced as the normalised channel separation) remains unchanged. The performance figures of the practical WDM devices are compared with the analytical predictions. It is found that, in general, the predicted results are in good agreement with the reported practical measurements of the optical crosstalk but, due to the simplicity of the modelling, a few variations are observed with some WDM systems