vertical bars in the lower portion of Understanding Optical Fiber a. Rayleigh scattering results in a wavelength dependence of 1/24. Figure 3.10 Optical fiber attenua- tion as a function of wavelength. a wavelength b. Light absorption. a wavelength c. Total attenuation from Rayleigh scattering and 1600 nm light absorption. a wavelength Chapter Three Figure 3.10, you will note three shaded areas. These areas represent com- mon transmission windows and define the wavelengths used for most optical transmission. Thus, instead of operating at any specific wave- length, both lasers and LEDs are designed to operate at specific frequen- cies, resulting in specific wavelengths that minimize attenuation. DISPERSION Although optical attenuation is an important character- istic governing the use of a fiber, it is not the only characteristic that governs performance. Another important characteristic is dispersion. Dispersion represents the smearing or broadening of an optical signal. This phenomenon results from the components of light that consist of numerous discrete wavelengths traversing the fiber at different rates. In an optical transmission system, dispersion results in the spreading of a pulse as distance increases. Thus, dispersion limits the maximum data transmission rate or information carrying capacity of a fiber. Fiber dis- persion varies with wavelengths and is denoted in terms of picoseconds (ps) per nanometer per kilometer. Figure 3.11 depicts the relationship between dispersion and wave- length. Fiber dispersion is controlled by the fiber design process, where the location at which dispersion equals zero is referred to as the zero-dis- persion wavelength. The zero-dispersion wavelength represents the wave- length at which a fiber's information carrying capacity peaks. For single- mode fiber the zero-dispersion wavelength is located at approximately 1310 nm. Another zero-dispersion wavelength is located in the 1550-nm region depicted by the second curve in Figure 3.11. This curve is associated with silica-base