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ICT Today Nov/Dec

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38 I ICT TODAY Multimode Optical Fiber Multimode optical fiber is the most common media choice for both backbone and horizontal distribution within the LAN including campuses, buildings, and data centers. With multimode, there are many modes of light, rather than one beam of light traveling down the cable as with singlemode. These modes travel down the cable at different speeds. As depicted in Figure 1, the white area in the middle is the fiber core surrounded by Cable manufacturers over the years have been able to reduce this dispersion, enabling increased distance or higher speeds over multimode cable. cladding. When light is sent into multimode cable, it is going to hit the cladding and then reflect up until reaching the point of the critical angle. As these modes advance at different angles, they will arrive at different times at the other end. The pulse of light placed at the front end is going to spread as it travels down the cable. The longer the fiber, the more spreading occurs. This is called dispersion. Inherently, dispersion is the effect of different delay times of the individual modes. FIGURE 1: Multiple modes of light, characteristic of multimode optical fiber cable. FIGURE 2: Multimode optical fiber types and distances.

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