Fibre Optic Impairments
There are two impairments associated with lightwave signals namely Attenuation and Distortion. Attenuation, or signal loss, in a fibre occurs because of absorption of the signal. Absorption may occur in three ways - Direct absorption occurs when some impurity in the core of the fibre stops a part of the signal. Secondly, Scattering occurs when part of the signal strikes an impurity in t.he core. It is then reflected into the cladding and absorbed. Finally, Refractive loss occurs when part of the signal strikes the boundary between the core and the cladding. It is then refracted, or bent, into the cladding and absorbed.
Distortion occurs when a part of the signal strikes the core/cladding boundary and is reflected back into the core. The reflected signal has farther to travel, and so arrives at the end of the fibre slightly later than the direct signal. One has to understand that Impairments are always there. They limit the capabilities of virtually every transmission system. The received signal always differs to some degree from the transmitted signal. When the differences are not acceptable, impairments need to be reduced.
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