 (AL) between adjacent AWGs equals an integer (m) multiple of the central wavelength (x) of the demultiplexer. As a consequence, the field distribution at the input aperture will be reproduced at the output aperture. Therefore, at this center wavelength, the light focuses on the center of the image plane (provided that the input waveguide is centered in the input plane). If the input wavelength is detuned from this central wavelength, phase changes occur in the array branches. Due to the constant path length difference between adjacent waveguides, this phase change increases linearly from the inner to outer AWGs, which causes the wavefront to be tilted at the output aperture. Consequently, the focal point in the image plane is shifted away from the center. By placing receiver waveguides at proper positions along the image plane, spatial separation of the different wavelength channels is obtained. AWG are able to process a great number of nearby channels with acceptable loss and a great reproducibility and their structure allows even bigger mux/demux to be designed by cascaded of suitably designed AWG. The performance of a realistic AWG used for multiplexing/demultiplexing DWDM channels is reported in Table 4.12. References 1. Snider, A. W., Love, J. D., Optical Waveguide Theory, Chapman & Hall, London, U.K., 1983, ISBN- 13: 978-0412099502. 2. Hunger, H. G., Planar Optical Waveguides and Fibers, Clarendon Press, Oxford, U.K., 1977. 3. Gloge, D., Weakly guiding fibres, Applied Optics, 11(10), 2252-2258 (1971). 4. He, Y., Shi, F., Beam Propagation Method and Microlens Design for Optical Coupling: Finite-Difference Full-Vectorial Beam Propagation Method Development and Microlens Design for Fiber to Laser Diode Coupling, VDM Verlag, Berlin, Dr. Müller, s.l., 2010, ISBN-13: 978-3639209723. Technology for Telecommunications: Optical Fibers, Amplifiers, and Passive Devices 5. Skutnik, B. J., Moran, K. B., Spaniol, S., Optical fibers for improved low loss coupling of optical, Proceedings of Progress in Biomedical Optics a