 have a dichroism ratio (ratio between the difference of the two polarization components power and their sum) within -19 dB. 9.5.4.2.7 Penalties Analysis Summary The summary of the penalties analysis is reported in Table 9.16. .The required SN, results to be 18.8dB. The draft design value is 22.4 dB, thus the system seems feasible. Nevertheless, it is a key point to verify the assumptions by simulation. From simulation, the required SNo results to be about 2 dB lower than that generated by the penalty addition rule, showing the fact that we are at the limits of validity of this method. Analyzing simulation data, we can see that several points emerge where different phe- nomena interact. The main interactions are All forms of crosstalk are a bit less effective due polarization fluctuations, channel asynchronous clock, and nonlinear polarization fluctuation The worst case model for the linear crosstalk results to be too pessimistic Also the FWM penalty model results to be pessimistic mainly due to the walk-off caused by polarization fluctuations Next Generation Transmission Systems TABLE 9.16 Summary of the Penalty Analysis for the 100 Gbit/s Ultra Long Haul System Adopting Constant Power 16-4QAM with Coherent Detection Native 100 Gbit/s Ultra-Long Haul System 16-4QAM Constellation constituted by the vertices of an 8H hexahedral Constant Power System length 9000 km Span length 30 km SSMF + 5km DCF - 257 spans Channel speed 100 Gbit/s Bilateral optical bandwidth 50 GHz, symbol rate 25 Gbsymbols/s Channel spacing 100 GHz 45 channels in extended C band - 4.5 Tbit/s capacity Ideal SN (dB) Overall optical bilateral bandwidth 76 GHz Ideal SNo (dB) Margin in dB Transmitter dynamic range External cavity tunable laser for transmission Linear crosstalk Overall Gaussian channel filtering function, Bo = 2.2R Nonlinear crosstalk FWM dominates CD-SPM-PMD 16 Stages MLSE, total ISI factor <2 Phase noise High output power external cavity laser, linewidth 250 kHz Nonlinear polarization SNo and BER plateau at SNo = 21.8 dB Aging Syst