 optical switches quite diffused to realize tunable optical add drop multiplexers (OADMs) (see Chapter 7). The scope of a WSS is essentially to eliminate from the input DWDM comb whatever set of channels is indicated by the network element control. The functional scheme of a WSS is shown in Figure 5.48: it is essentially a set of com- ponents integrating together the demultiplexer and the drop channel separation SO that the architecture of the single-side OADM is simplified. The implementation technology is similar to that of 3D MEMs, as shown in Figure 5.37. In the figure the incoming WDM comb is directed through a discrete 3D optics to a space diffraction grating that divides the different wavelength channels. The channels are successively deflected by the same spherical mirror that has sent them on the grating to a 3D MEMS that directs any channel on the desired direction. In particular, channels to be dropped are sent to one fiber among the array of WSS drop fibers, while channels that are to pass through are sent again on the grating to be multiplexed and deflected toward the output line fiber. This is not the only possible architecture for a WSS, but tunability is generally a characteristic of all WSSs, SO that any channel can be send to any drop port. At the beginning of their introduction there was a lot of suspicion on WSSs due to their characteristics of being completely built through discrete 3D optics: it was believed that they were unstable and unreliable, at least in the long run. Diffraction grating Front end LC/MEMS switch Spherical mirror FIGURE 5.37 Block scheme of a quite diffused WSS architecture. Telecommunication Networks This prediction, at least up to now, has been demonstrated to be unfounded and WSSs are at present the most affirmed technology for tunable OADMs. 5.7 Electronic Components When optical transmission was born, in the early 1990s, the industry was completely com- mitted to the development of optical components and there was a diffused idea that optics was going to replace alm