er a span of a transmis- sion fiber. Figure 6.24 shows how the chirped FBG is normally used with a circulator to ensure that the reflected pulse can continue on its path through the system. FBG dispersion compensators offer the advantage over DCMs of being low form factor components that do not contribute significant nonlinear crosstalk. Their loss is dominated by the circulator and is typically 1.5 to 2.5 dB for the double passage of the light. In contrast to DCMs, there is no need to include dedicated amplification. Moreover, chirped FBGs can be incorporated into optical add-drop multiplexers to perform simultaneous channel selec- tion and dispersion compensation (Ellis et al., 1997). Unfortunately, chirped FBGs operate over a much narrower bandwidth than NDF- based solutions and SO can only compensate for one or a small number of channels. Three challenges for grating manufacturers are To ensure that the group delay is spectrally uniform (i.e., free from high-frequency ripples) (Kashyap, 1999) To provide a means, such as athermal packaging (Lo & Kuo, 2002, 2003), to cancel any wavelength drifting of the reflectance profile To fabricate the grating with low polarization mode dispersion and polarization- dependent loss. (See the later discussion of PMD due to optical components.) Chromatic Dispersion: Mitigation Electronic Dispersion Compensation Electronic (Chromatic) Dispersion Compensation (EDC) has recently become a topic of active research (Chandrasekhar et al., 2006; Yu & Shanbhag, 2006; McGhan et al., 2006; McGhan, 2006). Its underlying principles have been understood for a number of years, but the High-speed Application-Specific Integrated Circuits (ASICs) to carry out the necessary processing were not available for application at 10 Gbit/s and 40 Gbit/s until recently. There are two categories of EDC, according to whether the operation is performed at the transmitter or at the receiver end of the system (McGhan, 2006). Indeed, it is possible to use both in a system, and EDC can be combined with other (o