Networks - OTDR Fault Finding

Characterise an optical fibre

Optical time domain reflectometry (OTDR) is used to identify and locate sources of loss by measuring fibre attenuation as a function of distance. This is achieved by launching pulses of light into optical fibre at recorded times, and detecting backscattered light. The pulse time-of-flight (TOF) is used to calculate the distance the pulse travelled. OTDR is successfully used for network maintenance, commissioning, troubleshooting, and restoration.


Attenuation is a measure of the total loss of signal between the input and output of an optical fibre link. Backscatter is a typical source of loss, and can be caused by passive optical components, fibre bends and breaks, connectors, or splices along the length of the fibre. OTDR characterises backscatter events, allowing an engineer to replace faulty or underperforming components so that attenuation is reduced.

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