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Computer Networks/Networks

Notes
Figure 3.9: Light Propagation in Single Mode Step index Fiber

It performs better than does multimode fiber over longer distances at higher transmission rates.
Due to reduced core diameter all the emitted light propagates along a single path. Consequently
the received signal is of a comparable width to the input signal. Although more costly, monomode
fiber is used to advantage in long haul, and especially in high bandwidth, applications.

Notes Singlemode fibers have the very broadest bandwidth, lowest cost and lowest
attenuation of any available optical fiber. Therefore, they are universally used in long-
distance telephony and cable television applications.

Advantages of Optical Fibers

Immunity to electromagnetic interference and crosstalk
No electrical ground loop or short circuit problems
Small size and light-weight

Large bandwidth for size and weight
Safe in combustible areas (no arching)
Immunity to lightning and electrical discharges

Longer cable runs between repeaters
Flexibility and high strength
Potential high temperature operation
Secure against signal leakage and interference
No electrical hazard when cut or damaged.

General Properties of Optical Fiber

Configuration: Fiber optic systems consist of light sources, cables and light detectors, as depicted
in Figure 3.10. In a simple configuration, one of each is used. In a more complex configuration
over longer distances, many such sets of elements are employed. Much as is the case in other
transmission systems, long haul optical communications involve a number of regenerative
repeaters. In a fiber optic system, repeaters are opto-electric devices. On the incoming side of the
repeater, a light detector receives the optical signal, converts it into an electrical signal, boosts

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