on rule, which holds with SO small indexes, the total ISI is 0.95. From Figure 9.60, we see that at such ISI, the optical compensator works very well and the residual penalty is lower than 0.1 dB. 9.5.3.2.2 Linear Crosstalk Linear crosstalk is very important, due to the large spectra of the chosen modulation formats with respect to the channel spacing that is determined by the already deployed system. A penalty of 1.0 dB is evaluated using the same model introduced in Chapter 6. Next Generation Transmission Systems 9.5.3.2.3 Nonlinear Crosstalk (FWM and XPM) Chromatic dispersion under compensation makes XPM to be less efficient. However, the effectiveness of this design tool is not as good as in the case of 10 Gbit/s due to the fact that the dispersion map results are not optimized for the new modulation formats. Applying the same model we have applied in Section 9.3.5, we derive in any case a neg- ligible XPM penalty. As far as FWM is concerned, the same model used in Chapter 6 can be reapplied here and the FWM-induced penalty is evaluated equal to 0.1 dB. 9.5.3.2.4 Nonlinear Polarization Fluctuations If nonlinear polarization fluctuations are present, they have a smaller effect with respect to the case of coherent detection. As a matter of fact the fast fluctuations of the Jones matrix that cannot be tracked by the tracking circuit are due to its tight bandwidth. Thus the overall effect is to smooth the Stokes parameters of a factor (1 - Ppol) and transfer a part of the signal power proportional to the depolarization ratio to the noise. Besides the plateau we have already introduced, the penalty relative to the depolariza- tion can be written as in Equation 9.81 resulting to be 0.6dB. 9.5.3.2.5 Summary of the Penalty Analysis The results of the penalty analysis are summarized in Table 9.14. At the end of the penalty analysis, the required SNo is exactly identical to that evaluated by the draft design. TABLE 9.14 Summary of the Penalty Analysis for the 8-DPSK and 8-PolSK 100 Gbit/s Designed to Work with a Line O