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SER
M
ANUAL
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Chapter
1
1
Measurement Principles
This chapter give the principle of measurement :
❏
for OTDR modules
❏
for OTS modules
❏
for the WDM modules
OTDR measurements principle
Optical time domain reflectometry consists of injecting a light pulse down the
optical fiber to be analyzed and observing, at the point of injection, the intensity
of the light reflected back in the opposite direction to the pulse propagation.
The detected backscattered (or retrodiffusion) signal is a decreasing exponential,
to which peaks caused by reflection from fiber connectors, splices or faults are
added.
Typical backscattered trace
Measurement result
The backscattered signal primarily allows the location of a segment of the fiber to
be found on the link.
Distance (km)
Relative
level (dB)
Reflectance
Attenuation
between
2 points
Attenuation due
to the connection
Reflectometer
Optical fiber
Connection
Splice
End of fiber
or a break
Attenuation due
to splice
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