y wide spectrum transmissions or multichannel dispersion in WDM systems. In the first case however, the distortion due to the spectral analysis of the channel and successive composition of the spectral components has to be taken into account. The com- pensator tuning is performed by using a cooler and exploiting the thermal dependence of the optical characteristics of the silica composing the AWG and the lens structure. An improvement of the performance of the TODC can be attained by realizing several lenses monolithically integrated into the structure of the chip SO that the whole device is Telecommunication Networks Lens Flat mirror Circulator FIGURE 9.6 TODC based on a cyclic AWG. Slab waveguides FIGURE 9.7 Differential Delay of the AWG based TODC versus the temperature. (After Ikuma, Y. and Tsuda, H., IEEE J. Lightwave Technol., 27(22), 5202, 2009.) Wavelength deviation from 10 = 1552 nm a planar silicon on silica-integrated circuit. The characteristics of an experimental realiza- tion of the device are reported in Figure 9.7 (3]. Another technology used to implement experimental TODCs is based on discrete optics and on technologies similar that used in 3D Micro Electrical Mechanical machines (MEMs), Liquid Crystal on Silicon (LCOS) switches and in Wavelength Selective Switch (WSS) components (see Chapter 5 for MEMs switches and Chapter 6 for WSS). An example of TODC using this technology is reported in [5] and its block scheme is shown in Figure 9.8. A circulator deviates the whole DWDM comb into an AWG where the channels are demultiplexed. At the AWG output, a free space optics directs the demulti- plexed channels on a bulk grating and, at the grating output, a lens focalizes the channels on an LCOS switch. The LCOS reflects back the channels that traverse the system again in the opposite direction to be reinjected by the circulator into the transmitting fiber after multiplexing by the AWG. The AWG, the LCOS deflector, and the Brag grating, all provide dispersion and, if the dispersion axis of the grating i