Impact of Random Group Delay Ripple on the Cascadability of Wavelength Select Switches for Nyquist-Pulse-Shaped Signals

We report on the impact that the random group delay ripple of wavelength select switches has on Nyquist-pulse-shaped signals and on the cascadability of wavelength select switches (WSSs) for use as wavelength-based routers within optical communication networks. We show how to simulate the appropriate WSS filter response that accounts for the random group delay ripple and use this within a numerical simulator to predict the performance of communication networks based on WSSs. We find that the random group delay ripple could lead to large bit error rates in recirculating loop experiments, whereby the signal sees the same group delay upon each pass through the loop; though, as in a realistic network, if independent WSSs with uncorrelated group delay ripples are concatenated together then we predict that the system performance would be limited by the accumulated amplified spontaneous emission noise in the network. These results indicate the suitability of WSSs to construct large scale networks with wavelength-based routing functionality extending over 30 switching nodes.