r at the transmitter that we will assume a single- stage amplifier optimized to perform as booster and at the receiver a preamplifier will be present. The booster and preamplifiers noise figures will be NF and NF, respectively. To provide an example of numeric performance evaluation, we will assume that the transmission fiber is an SSMF and that the values of the various system parameters are those reported in Table 6.2. An exact evaluation of the noise at the amplifier chain is complex due to the fact that the electromagnetic field propagating in a generic system span is not in a minimum energy state due to the ASE contribution of the previous amplifiers [11]. The result of the exact quantum mechanical evaluation of the overall noise is reported in [19]. However, in a realistic telecom- munication case, amplifiers are low-noise high-gain components, SO that the only noise term that is relevant after detection among the noise processes caused by the amplifier chain is the so-called beat noise, that is the beat between the signal and the accumulated ASE. TABLE 6.2 Parameters for the Design Examples of DWDM Amplified Systems In-line amplifiers input saturation power P (dBm) In-line amplifiers output saturation power pout (dBm) Booster amplifiers input saturation power (dBm) s,booster Booster amplifiers output saturation power s,booster (dBm) Preamplifiers input saturation power s,preamp (dBm) Preamplifiers output saturation power s,preamp (dBm) Amplifiers noise factor (all the amplifiers) NF (dB) Multiplexer demultiplexer loss (128 channels) Extra losses at the transmitter Extra losses at the receiver Amplifier insertion loss Transmitter output power (injected in fiber) PL (dBm) SSMF fiber loss a (dB/km) Receiver sensitivity @10 Gbit/s Srec (dBm) Receiver saturation power PsRec (dBm) Transmission Systems Architectures and Performances In this hypothesis, every amplifier introduces an optical noise whose power is given by oj=hwBGjNFj(j=1,..,Na) (6.48) where B is the unilateral optical bandwidth. Here it is necessary