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Chapter 1:
WDM, Fiber to the X, and HFC Systems: A Technical Review
Fiber optics is mature technology. It was used at the beginning of the eighties for computers’ local networking using light emitting diodes (LEDs). One of its major advantages over traditional “copper lines” and “coax lines” is the virtually infinite bandwidth of the fiber line, which translates into a higher data rate capacity and therefore more users per line. This advantage can be expanded when several wavelengths are transmitted through the same fiber, where each wavelength carries wide band data. This method is called wavelength division multiplexing or WDM. The second main advantage of a fiber optics line over a regular “copper line” is its low-loss nature, traditionally 0.15 dB/km. The traditional coax will lose half of the input power within a few hundred meters. In comparison, a good-quality fiber will lose half of its input power after 15 to 20 km. This means less retransmit and fewer nodes required to amplify the signal. It is known that the transmitted distance depends on the input power to the fiber losses and the receiver sensitivity. An additional advantage of fibers is their immunity to any kind of magnetic interference from the outside. Hence, there will be fewer problems related to surge protection to take care of during deployment. Furthermore, since the fiber does not emit any electromagnetic radiation, it is considered to be an ideal line that cannot be tapped. One more advantage over the coax is the fiber diameter of 10–50 microns. Thus, one fiber cable, which contains many fibers, results in a higher data rate per cable and higher data capacity.
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