d no PMD. System parameters are reported in Table 6.1 but for fibers parameters that are reported in Table 4.2. Transmission Systems Architectures and Performances As noted in the previous section, pulse broadening has the effect to transfer energy from one bit period to the adjacent one. If this causes energy to be transferred from a one to the adjacent zero, the signal dynamic range is reduced and the BER degrades. This phenom- enon is also called intersymbol interference (ISI). The presence of ISI has a different effect with respect to the noise on the BER curve. Increasing the noise power a greater value of the received power is needed to achieve the same SN and then the same BER. However, whatever the required BER, it can be achieved, at least theoretically, transmit- ting a sufficiently high power. In the case of ISI, both the energy detected on a "one" and the energy transferred to the adjacent time slots increase proportionally to the transmitted power. Thus, the ratio between the energy that remains in the right time slot and the disturbing energy is con- stant and no increase of the signal power can change it. This causes a change of shape of the BER curves and it is expected that the penalty would rise much faster than linear increasing pulse broadening. The chromatic dispersion penalty can be evaluated from the BER and it is plotted in Figure 6.8 where the foreseen rapid increase of the penalty can be verified. From the figure, a limit distance of about 36 km is estimated for transmission on SSMF at 10 Gbit/s, while about 132 km are derived for transmission on NZ+. To understand the penalty trend, when the bit rate changes, in the figure, also a curve relative to 40 Gbit/s on an NZ fiber is shown indicating for this case a dispersion limit of 11 km; thus, the dispersion-limited distance decreases approximately of a factor 16 passing from 10 to 40 Gbit/s. This is a general trend that can be easily verified using the performance evaluation method detailed in this section: the dispersion limit decreases 