Photonic Network Communications, 3:3, 237±243, 2001 # 2001 Kluwer Academic Publishers. Manufactured in The Netherlands. Impact of Fiber Non-linearity in High Capacity WDM Systems and in Cross-Connected Backbone Networks Stefano Binetti 1 CoRiTel - Consorzio di Ricerca sulle Telecomunicazioni via di Tor Vergata 110, Rome, Italy Svetlana Chemiakina, Roberto Sabella Ericsson Telecomunicazioni, R & D Division v. Anagnina 203, 00040 Rome, Italy Received July 10, 2000; Revised January 10, 2001 Abstract. The rapidly increasing data traf®c volumes will demand for very high transmission capacity and network nodes' throughput. Wavelength division multiplexing (WDM) technology will be asked to support many channels on the same ®ber, both in point-to-point links and in WDM optical networks. The transmission of a high number of wavelength channels in all these systems is a key issue. This paper analyzes this topic, in both high capacity links and optical networks, highlighting the impact of ®ber non-linearity, and addressing the main source of impairments. This is done through the use of a semi-analytical model recently upgraded to account for all the contributions deriving from Kerr effects, particularly four-wave mixing and cross-phase modulation. The analysis reveals that more than one hundred of channels at 2.5 Gbit/s can be transmitted in point-to-point links whose length can span until the order of 1000 km, and 32 channels per ®ber, at the previous bit rate, can be handled in WDM networks, without dispersion compensation. For a higher number of channels (e.g., 64) dispersion compensation is needed. Keywords: WDM networks, non-linear effects, Kerr effect 1 Introduction The rapid growth of data traf®c, mainly driven by the great expansion of the internet traf®c, and the perspective of new communication services demanding for even more bandwidth, lead to a strong demand for increasing both transmission capacity and network nodes' throughput. This leads to the realization of wavelength division multiplexing (WDM) systems employing a high number of wavelength channels for point-to-point communica- tion systems, and to the achievement of robust, ¯exible, and scaleable optical backbone networks. The transmission performance is a key factor for the realization of such systems. Besides chromatic dispersion, ampli®ed spontaneous emission (ASE) noise accumulation induced by optical ampli®ers, and crosstalk effects, ®ber non-linearity becomes one of the most limiting factors to the transmission of a large number of WDM channels. The impact of non-linear effects on the perform- ance of high-speed WDM communications systems has been largely investigated in the literature. When the number of channels is large, the impact of non- linearity becomes increasingly important. However, the main dif®culty, when evaluating the performance, is to simultaneously take into account all the effects, in addition to technological issues relating to the devices employed in the system. In order to evaluate the performance of complex WDM systems, either considering high-capacity point-to-point links or WDM networks, we developed a semi-analytical model ([1] and [2]). This model allowed the performance evaluation taking into account chirping/dispersion, four wave mixing (FWM), and self-phase modulation (SPM), in addition to the models of the considered optical devices. Recently, we have upgraded the model, to account for the cross- phase modulation (XPM) effect. The aim of the present paper is the investigation of the impact of non-linearity and the interplay among the different non-linear contributions in two relevant cases: (i) high capacity point-to-point links; and (ii) WDM optical transparent networks employing optical 1 S. Binetti is now with Cisco Systems.