ure and Performances Due to this reason they cannot be used in the second stage of the WI, where the incoming signal frequency is not fixed. At the present technology state, the input/output loss of a practical WI is really high as it can immediately be evaluated, for example, considering a 322 WI. Assuming that wave- length converters are transparent and summing the loss of 5 dB due to the input AWG to the huge loss of 15 dB due to the 32x output coupler, a theoretical loss as high as 20 dB is reached, to which in a realistic case additional losses coming, for example, from connec- tors have to be added. Such a loss, added to the complex structure of the WI, makes unpractical the use of such devices, even if there is a sufficiently stable technology to realize them. A different way to realize a WI is leveraging on the integration of different optoelec- tronic devices onto the same InP-based chip. In Chapter 5 we have seen that besides other components, also semiconductor optical amplifiers (SOAs) can be realized essentially with the InP laser technology. If it is not easy to use SOAs for WDM applications, they can work much better as single- channel amplifiers, SO that a WI realized with the scheme of Figure 7.25 can be realized using a small number of InP optoelectronics integrated chips (the example of a 32 WI is considered in the figure). Moreover, several methods exist to integrate a wavelength con- verter into an InP circuit. Assuming that an integrated wavelength converter will lose dB, a standard SOA can easily gain 20 dB on a single channel without the need of any particular design trick, SO to arrive at a global WI loss of 4 dB that is acceptable for applications. However, this solution, although interesting, is not practical for two main reasons. The first is that the SOA presence is paid with the introduction of ASE noise and this reduces the optical propagation performance of the signal, the second, and more impor- tant reason is that the cost of a subsystem with the structure of Figure 7.25 is huge 