 system length, one should understand the technique or techniques used to estimate the bandwidth X length product of the fiber. Some of the key parameters of the Corning InfiniCor graded index fiber (see Figure 5.11 for losses) are summarized in Tables 5.1 and 5.2. Similar fibers are available from other manufacturers. The multimode fiber was introduced and discussed up to now with the tacit assumption that there are a large number of modes, but their number was not stated. This question will be addressed now. To derive the number of modes supported by a given multimode fiber, Table 5.1 Attenuation of Corning InfiniCor Fiber Wavelength (nm) Maximum value (dB/km) Source: Corning Inc. Data Sheet, January 2008 Issue. Chapter 5 Optical Fibers Table 5.2 Bandwidth X km Performance of Corning InfiniCor Fiber High-performance 850 nm Legacy performance Corning Optical Fiber only (MHz X km) (MHz X km) InfiniCor® eSX+ InfiniCor® SX+ InfiniCor® SXi InfiniCor® 600 Source: Corning Inc. Data Sheet, January 2008 Issue. the Maxwell equations must be solved in the context of the fiber structure (cylinder) and the material (dielectric, glass). From such an analysis a very useful quantity emerges called normalized frequency, V. It combines the wavelength, the physical dimensions of the fiber, and the properties of the dielectric (glass), and is given by (5.33) where a is the core radius, A is the relative refractive index difference, and A is the wavelength. It can be shown that the number of modes supported by a step index multimode fiber, Mstep, is (5.34) and by a graded index multimode fiber (5.35) where a is the refractive index profile parameter. For a parabolic profile (a = 2) the number of modes is Mgraded = V2/4=Mstep/2. = Consider a multimode fiber operating at 1300 nm with radius 25 um, n1 = 1.5, and A=2%. Then the step index fiber supports guided modes With a parabolic refractive index profile the same fiber will support 156 guided modes. The number of modes and their fluctuations can impair the performance of a multimode