Principle Of Reflectometry Measurements; Information Yielded By The Measurement - Viavi 8100 V2 Series User Manual

Chapter 1 Principles of measurement

Principle of reflectometry measurements

Principle of reflectometry measurements
Optical time domain reflectometry consists in injecting a light pulse into one end of the
optical fiber to be analyzed and observing, at the same end, the optical intensity passing
through the fiber in the opposite direction to the propagation of the pulse.
The signal detected is exponentially diminishing in form, typical of the phenomenon of
backscattering, with superimposed peaks due to reflections from the ends of the fiber or
other variations in the refractive index.
Figure 1 Trace showing typical backscattering

Information yielded by the measurement

From a backscatter trace it is possible, in particular, to determine the position of a section
of fiber within a link. The measurement result must reveal:
• the attenuation
• the location of faults, by their distance from a point of origin,
• attenuation with respect to distance (dB/km)
• the reflectance of a reflective event or a link.
2 User Manual 78000010220 Rev. 024