Section 3. Basic Otdr Information; Principle.of.otdrs; Basic Definition And Classification Of Events; Reflection Events - Textron GREENLEE 920XC-13A Manual Del Usuario

Section 3. Basic OTDR Information

Principle of OTDRs

Basic Definition and Classification of Events

920XC-13A • 920XC-15A • 920XC-20C Instruction Manual
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An OTDR (Optical Time Domain Reflectometer) is a measurement instrument for identifying
optical fiber transmission features. The OTDR is used to measure the overall attenuation of a
fiber optic link and to provide details relating to the position of each event in that link. Events
include splices, connectors, bends, and optical components. Its non-destructive, single-ended
connection and rapid measurement have made the OTDR an indispensable tool for manufacturing,
construction, and maintenance of optical fiber links.
The faults and heterogeneity of optical fiber itself cause Rayleigh scattering of light transmitted in
optical fiber. Part of the light pulse is scattered in the reverse direction, and this is called Rayleigh
backscattering, which actually provides attenuation details relating to fiber length.
Information relating to distance is obtained through time information (thus "time domain" in the
name OTDR). Fresnel reflection occurs at the boundary between two media of different IOR (for
example, connections of faults, connectors, or optical fiber end). This reflection is used to locate
the discontinuous points on optical fiber. The magnitude of reflection depends on the difference
between.IOR.and.the.smoothness.of.boundary.
An OTDR sends out a light pulse into the optical fiber and receives reflections of events and
backscattering power of the pulse in time. Locations will be displayed on the LCD. The y-axis is
the dB value of backscattering power, and the x-axis is the distance.
Events refer to any abnormal points causing attenuation or sudden change of scattering power
besides the normal scattering of optical fiber, which include losses such as bending, connections,
and.ruptures.
Event points displayed on the LCD are abnormal points that cause traces to deviate from a straight
line.
Events can be classified as reflection events or non-reflection events.

Reflection Events

When some pulse energy is scattered, reflection events occur. When reflection events occur, a peak
is displayed on the trace (Figure 3-1).
Figure 3-1. Reflection Event
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