ndex increases speed 400% over step index. The graded in- dex cable varies the speed of different light paths in the core. This cuts down on pulse widening (distortion) also called modal dispersion. Fiber optic cable is often used as a backbone cable such as a building riser cable. It may also be used between Local Area Networks. It is seldom run to each desk. Advantages of fiber optic cabling are as follows: Fiber optic cable carries large amounts of data at a very high speed. Since the information is being transmitted by light 258 V The Telecom Handbook CHAPTER 12 Figure 12.5 Index The structure Input Output Profile Pulse Pulse of the fiber determines how light propagates through it. Multimode Step Index Multimode Graded Index Singlemode Step Index - Compliments of AMP, Jim Loizides and The Hylan Group Figure 12.6 BUFFER CLADDING The concentric layers of an optical fiber include the light-carrying core, the cladding, and the protective buffer. - Compliments of AMP, Jim Loizides and The Hylan Group The Telecom Handbook << 259 CABLE energy rather than electrical energy, the signal is not subject to the electrical properties of wire such as resistance and in- ductance which can attenuate the signal. Signal loss (diminishing strength as the signal moves along the cable) is significantly lower than for either coaxial cable or twisted pair. The signal is unaffected by electromagnetic frequency inter- ference. Fiber cables do not produce any electromagnetic noise, nor are they affected by it. There is no need for con- cern about cross talk, echoing or static. Fiber optic cable eliminates all grounding problems since it uses optical cou- pling instead of electrical coupling. Fiber optic cables carry no electrical energy SO there is no possibility of an electrical spark. Thus, the cable can be used in potentially explosive environments such as chemical plants and refineries. Fiber optic cables are far more secure than twisted pair or coaxial cables. There is no electromagnetic field. It is very difficult to tap into a f