 um at 1550 nm Source: Copyright © 2005 Furukawa Electric North America, Inc. available low loss window of the silica fiber into a number of bands whose exploitation will depend on the availability of the relevant technology. A summary of the optical bands and their respective wavelengths is summarized in Table 5.7. A number of fibers have been introduced to address the use of these optical bands. The aim is to reduce the amount of dispersion in the intended band of operation and also to minimize the impact of fiber nonlinearities. According to the ITU-T G.655 recommendations, the dispersion over the C-band should lie in the range 1 to10 ps/ (nm X km). Then the opera- tion can be extended into the L-band because the dispersion will still be low there. Both C- and L-bands are used for long haul applications. ITU-T recommendation G.656 is designed to extend operation into the S-band. With chromatic dispersion in the range of 2 to 14 ps/(nm X km) from 1460 to 1625 nm, this fiber can be used for Coarse WDM (CWDM) and Dense WDM (DWDM) throughout the S-, C-, and L-bands. These fibers are referred to as Non-Zero Dispersion-Shifted Fibers (NZ-DSF). A summary of the performance of the Furukawa Electric North America, Inc., NZ-DSF fiber is given in Tables 5.8 and 5.9. The dispersion of the NZ-DSF at 1550 nm is nearly four times less than that of the standard single-mode fiber, reducing the amount of dispersion compensation needed in Special Fibers Standard Single-Mode Fiber TrueWave REACH LWP Fig. 5.19 Use of NZ-DSF in a coarse WDM channel allocation scheme. Source: Copyright © Furukawa Electric North America, Inc. Wavelength (nm) long-haul systems (see Chapter 6). The reader should be aware that all leading fiber manu- facturers market NZ-DSF fiber. A significant part of the cost of DWDM systems is the cost of the narrowband active and passive optical components required by the specifications. The availability of the NZ- DSF fibers has enabled a substantial reduction of the cost of WDM by spacing the channels at 20 nm. Th