gth components are the fastest. The chromatic dispersion coefficient is wavelength dependent. However, there is no analytical expression for the wavelength variation of refractive index of the various fiber glasses and SO it is convenient to fit empirical equations to experimental data. Manufacturers often use equation 6.29 for "standard single-mode fiber" (Mynbaef & Scheiner, 2001): Chromatic Dispersion: System Implications Ao: Commonly 1310 nm So: Typically 0.092 ps/ (km nm² Permitted spread of values in the C- and L-bands Fig. 6.18 Typical wavelength variation of chromatic dispersion for a standard single-mode fiber, showing the approximate range of values in the C- and L-bands that conform to ITU-T recommendation G.652. Wavelength (nm) D(2)= (6.29) The constant 20 is the wavelength of zero dispersion. So = S(20) is the gradient, otherwise known as the "dispersion slope," dD(A)/d2, evaluated at 2=20. For fibers that comply with the ITU-T G.652 standard (ITU-T G.652), 20 should lie in the range 1300 to 1324 nm, which can be achieved with appropriate selection of refractive indices and core diameter. Equation 6.29 is plotted in Figure 6.18, which indicates the range of values in the C- and L-bands. Typically D is about +17 ps/ (km.nm) at 1550 nm. System Tolerance of Chromatic Dispersion Let us now consider the time domain. Dispersive pulse broadening causes the logical 1s to spread into one or more adjacent bitslots in a process known as "Intersymbol Interference" (ISI). When a 1 is neighbored by Os the optical energy within the 1 bitslot is reduced and transferred to the Os. However, consecutive 1s interact in a more complicated manner. Interference occurs between them and can cause peak powers that can be much greater than twice the time-averaged channel power. By considering equation 6.21, we can see that the photoelectric currents that constitute the Q value at the receiver are affected because the values of I can be increased while the values of I can be either raised or lowered, depend- ing on their positi