mon Optical Fiber Types Deployed in Terrestrial Networks At 1550 nm Effective Chromatic Dispersion Fiber Type Specification Area (um ² (ps/nm/km) Standard single-mode fiber (SSMF) G.652 Dispersion shifted fiber (DSF) G.653 Non-zero dispersion shifted fiber (NZDSF) G.652 ~55-75 Fiber optic cables are made from thin strands of very pure glass roughly the diameter of a human hair and capable of acting as a waveguide carrying optical signals around corners long distances with minimal distortion and loss [1]. Each fiber has a core that provides the medium in which light is transmitted, a cladding that reflects light back into the core when there are bends, and a buffer layer that provides mechanical protections and strength. Table 13.1 lists the three most common types of optical fiber deployed in terrestrial optical net- works, along with their approximate chromatic dispersion and effective area. The attenuation of all three fiber types is typically between 0.2 and 0.25 dB/km. It is now established that, of the three fiber types in Table 13.1, SSMF is optimum for state-of-the-art, 100 Gb/s-per wavelength optical systems utilizing coherent detection and digital signal processing in the receiver for impairment mitigation [2-4]. The core network can have wide geographic reach. In AT&T's case, the fiber-optic network includes more than one million fiber route miles globally, and consists of three main segments: dense metro networks serving customers within a city or region, long-haul networks that spans the United States to provide intercity connectivity, and an international fiber network connecting mul- tinational customers. AT&T's domestic intercity optical backbone network is shown in Figure 13.2. Denser regional and metro fiber deployments also exist but make the chart too busy to be meaningful. High fiber-count cables that bundle typically several hundred fibers are deployed in a mesh network architecture. FIGURE 13.2 AT&T domestic 100G long haul optical backbone. Building the Network of the Future 13.1.1 OPTICAL T