g to a bit error rate (BER) of 10-12 passes from 15.4 to 18.3 to 20 dB. This is a correction not completely insignificant to the value ASN, = 10 dB that was estimated at first glance if a fixed error probability has to be maintained passing from 10 to 100 Gbit/s. Naturally, this does not mean that the performances get better by increasing . As a matter of fact, if we take into account the increase of the ASE bandwidth related to the increase of Moer we discover that the power needed to achieve an error probability of 10-12 slightly increases by 6% passing from = 2 to = 3 and increases again by another 3% passing to Moe = 6. In any case, considering the SNo, any change in has to be considered. In Chapter 6, we have seen that in an optically amplified line, the ASE spectral density is proportional to the number of spans, thus to the link length. Let us imagine having a link 2500 km long designed for 10 Gbit/s, constituted by 50 spans of 50km each. If the Optical Signal to Noise ratio has to increase by 10 dB passing to Telecommunication Networks 100 Gbit/s, this means that, once the transmitted power is fixed, whose value is determined by the nonlinear effects, the link has to be shortened by a factor 10. In other words, the combination of nonlinear effects limiting the transmitted power and the increase of ASE noise causes a signal at 100 Gbit/s to propagate for a distance 10 times smaller with respect to a signal at 10 Gbit/s. Besides improving the amplifiers design to reduce the noise factor, there is no other way of compensating the ASE effect. On the other hand, we know from Chapter 4, that optical amplifiers are quite near the ideal quantum performances, thus there is no great improvement to attain from amplifiers design, at least as far as quantum coherent states are propagated into the fiber. It is possible to design parametric amplifiers, where the ASE noise spectral density is not uniform along the different polarizations. If a parametric amplifier is used to reduce the ASE along a polarization at the exp