and is currently the preferred operating area for optical fiber installed since 1990 or SO. There are two "bands" within the range of wavelengths noted above. The C-band range is 1530 to 1570 nm, while the L-band range is 1570 to 1610 nm. OPTICAL WINDOW UTILIZATION The use of the first optical window is for short-wavelength multimode systems. In comparison, the second optical window is used for long wavelength multimode or single- mode transmission systems. Single-mode fiber is used primarily for long-distance carrier systems. The ITU G.652 specification for optical fiber is optimized for a 1310 nm Team-Fly® Understanding Optical Fiber wavelength and is referred to as non-dispersion-shifted fiber (NDSF). A sec- ond ITU specification, G.653, refers to dispersion-shifted fiber (DSF) and was designed for minimal dispersion in the C band. As wavelength divi- sion multiplexing (WDM) systems emerged, a defined level of chromatic dispersion was recognized to have a positive effect on the ability to place multiple light signals on a common fiber. This resulted in the promulga- tion of the ITU G.655 standard for non-zero-dispersion-shifted fiber (NZDSF). NZDSF fibers designed for long-distance carrier systems have a moderate amount of dispersion in the C and the L bands. Today the C and L bands are being used for dense wavelength division multiplexing (DWDM). In Chapter 4 we will discuss optical multiplexing as well as the use of optical amplifiers that make this technique of placing multiple signals on a fiber economically possible. Fiber Composition Three types of material can be used to manufacture fiber-optic cable: glass, plastic, and plastic-clad silica (PCS). The use of each type of material results in differences in the cost of the cable as well as the amount of attenuation that light pulses experience as they flow down the cable. Concerning the latter, attenuation results primarily from two physical phenomena: absorption and scattering. As light in the form of photons flows along the core of a fiber, the photons 