 silica glass Absorption by molecular vibration of OH index in the core (Fig. 6.1-11). Absorption by transition metals Structural imperfections 6.1.2.2 Attenuation Geometrical nonuniformity at core-cladding boundary Imperfection at connection or splicing between fibers Attenuation is a very important factor in designing From Ref. [3]. effective long-distance fiber optic networks. Conse- quently, the fabrication methods have improved dra- matically during the past 30 years SO that attenuation is measured in a few tenths of a dB/km. The dB is defined into micro- and macro-bending losses. Micro-bending in Eq. (6.1.19). The various factors affecting the atten- losses are due to nanometer-size deviations in the fiber. uation, in the 0.8- to 1.6-um wavelength region, are listed Macro-bending losses are due to visible bends in the in Table 6.1-4. Figure 6.1.12 shows schematically how fiber. Figure 6.1-14 shows qualitatively how micro- and some of the factors contributing to the overall light at- macrobends contribute to the overall loss in a SM and tenuation vary with the wavelength in the near-infrared MM fiber. wavelength region. Typical total losses for an optical fiber, at the three different transmission windows at 800, 1300, and 1550 nm, are 11 2 or 3, <0.5, and <0.2 dB/ Wavelength (um) km, respectively. These numbers are for SM fibers; from Fig. 6.1-13 it can be seen that MM fibers have slightly higher losses. The losses dealt with to date have been due to either intrinsic properties of the glass or extrinsic properties (such as OH and transition metal contents) that come from the particular fabrication method Total loss used. In addition, there are bending losses. If the fiber (experimental) has been improperly cabled or installed these bending losses can be substantial. Bending losses are divided Total loss (estimated) Rayleigh scattering loss Infrared Al2O3 absorption loss Ultraviolet absorption loss Loss due to imperfections of waveguide Dopant, Mole % Photon energy (eV) Fig. 6.1-11 Influence of different dop