 increase bandwidth over an existing fiber plant. It allows one to create multiple "virtual fibers" over one physical fiber. It does this by transmitting different wavelengths (or colors) of light down a piece of fiber [18]. DWDM was first adopted by long distance carriers because the spending in amplification, dispersion compensation, and regeneration made up most of the network equipment cost in regional and national SONET networks. DWDM became more and more popular in metro networks when the local exchange carriers grew their networks. Other than fiber exhaustion, traffic volume is the major economic factor for deploying DWDM technology in metro networks. DWDM operates in the range between 1530 and 1565 nm, the so-called C-band that corresponds to the low-loss window of the optical fiber. This is also the range where the Erbium doped optical amplifier² is operative. A grid of allowable wavelengths/ frequencies of operation is specified by ITU-T, centered at a frequency of 193.1 THz, or a wavelength of 1553.3 nm, and all frequencies spaced at multiples of 25 GHz (=0.2 nm) around that center frequency. Commercial systems can have channels at 2.5, 10, and 40 Gbps (where the latter are recently becoming commercial) as well as combinations of these in the same system. The higher the bit rate, the higher needs of the power budget meaning that the lasers need to have better signal to noise figures, the amplifier spacing needs to be reduced, amplification needs to be higher for example, by employing two amplifiers in series. Typically 64 channels at 10 Gbps reach a maximum distance of around 1500 km with an amplifier spacing of around 100 km. Long distance transmission systems beyond 1500 km and up to 4500 km are also commercially available using advanced and more expensive systems. The DWDM layer is protocol and bit rate independent, which means that it can carry ATM, SONET, and/or IP packets at the same time. WDM technology can also be used in Passive Optical Networks (PONs) which are access networks in which the en