onnector loss factors However, the glass in an optical fiber can be altered by are shown in Table 6.1-6. The local loss factors can be intense laser light [25, 26]. This fact has led to the calculated using the formulas in Section 6.1.1.4. The manufacturing of so-called fiber Bragg gratings (FBG). distributed losses are due to changes in the model These in-core fiber gratings have revolutionized optical launching conditions [15]. fiber communications systems, [27, 28]. The FBGs can Connector losses can be as high as 0.5 dB (this cor- be used for dispersion compensation [29], filter appli- responds to an additional km of fiber at 1.3 um). With cations [30], mode conversion [31], gain equalization [32], and wavelength multiplexing [33]. FBGs were first discovered in 1978 by Hill et al. [25]. These early grat- ings were created by the interference between forward and backward traveling waves in the fiber. The backward traveling wave comes from Fresnel reflection at the output end. At the crests of this interference pattern, Joint loss where the light is the strongest, interactions between the light and Ge defects in the glass alter the refractive index An = 10-3-10-5. The periodicity of these gratings is given by Local Distributed (6.1.40) where neff is the effective index of the fundamental mode. Evident from equation 6.1.40 is the fact that for a given laser only one periodicity can be produced. Not Link length very practical! Because the interaction between the light Fig. 6.1-31 Local and distributed (transient) losses and their launch and the defects is optimum for a small wavelength dependence. Reprinted from Ref. [15], p. 4.40, courtesy of region in the UV one cannot just change laser to obtain McGraw-Hill. a new grating periodicity. It was therefore a major CHAPTER 6. 1 Optical fiber, cable and connectors Insertion Loss Performance Insertion Loss difference (MM enhanced ferrule, 62.5/125 um fiber) between two channels (MM enhanced ferrule, 62.5/125 um fiber) Avg.: 0.13 dB Std. Dev.: 0.05 dB Avg.: 0.08 dB Std.