Fiber-optic communication uses light signals and so transmissions are not subject to electromagnetic interference. Fiber-optic cables act as a waveguide for light, with all the energy guided through the central core of the cable. The light is guided due to the presence of a lower refractive index cladding surrounding the central core. None of the energy in the signal is able to escape into the cladding and no energy is able to enter the core from any external sources. The composition of the cable is shown in Figure 3.15.
Since little of the light signal is absorbed in the glass core fiber-optic cables can be used for much longer distances before the signal must be amplified, or repeated. Some fiberoptic segments can be many kilometers long before a repeater is needed. Data transmission using a fiber-optic cable is many times faster than electrical methods and speeds of over 10 Gbps are possible. Fiber-optic cables deliver more reliable transmissions over greater distances, although at a somewhat greater cost. Cables of this type differ in their physical dimensions and composition and in the wavelength(s) of light which the system transmits.
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