Impact of WSS delay distortion on the ROADM cascade performance in virtual carrier-assisted DD multi-band OFDM metro networks

The performance of a cascade of reconfigurable optical add/drop multiplexers (ROADM) in direct-detection multiband (MB) orthogonal frequency-division multiplexing (OFDM) virtual carrier-assisted metro networks is studied using numerical simulation. In particular, the impact of the delay distortion of the wavelength-selective switch (WSS) on the network performance is analysed and discussed. To this aim, an extension of a physical model of the WSS is proposed to predict the phase response of the WSS. The study is performed for 42.8 Gb/s single-side-band MB-OFDM systems comprising 3 or 4 OFDM bands and operating with 25 GHz channel spacing. Optimized parameters for a Gaussian and 2nd order super-Gaussian band-selector are used. It is shown that the delay distortion of typical WSSs has a negligible impact on the network performance. The reduction of the overall filtering passband of the ROADM cascade is identified as the main factor of performance degradation.