Manual

9
Fiber Attenuation Overview
For any optical fiber link, we need to know the loss or attenuation of the cable or link to ensure it meets system
requirements and is ready to survive network aging and environmental effects. As the light signal traverses a fiber, it
decreases in power level. The decrease in power level is expressed in (dB) or as a rate of loss per unit distance (dB/Km).
ReceiverSource
P
in
(Emitted power)
P
out
(Received power)
Attenuation is caused by:
y Absorption of light by impurities within the fiber
y Scattering losses from variations in the silica structure within the fiber
y Bending losses due to over tightening of clamps or cable ties
y Contaminated or damaged connectors of the equipment and patch panels
Attenuation is the most critical parameter to look at in fiber optic networks.
Fiber loss is not a deterministic process that always behaves in the same way. There are many different factors that
can produce signal loss in the fiber link, including fiber impurities and poor installations. During transmission, losses
also occur when light is injected and by the differentcouplings and junctions made by connectors and splices.
For a fiber optic span, the effects of passive components and connector losses must be added to the inherent
attenuation of the fiber in order to obtain the total signal loss.