Chapter Iii Optical Time-Domain Reflectometer Module - Yamasaki Y30 Series User Manual

5 Introduction to the OTDR
5.1 The measuring Purpose of the OTDR
An OTDR displays the power of the returned signal related to distance. The information can be
used to confirm the transmission quality of a fiber optic link.
5.1.1 Measuring Contents of the OTDR
Position (distance) of event, result or fractured position of fiber optic link;
Attenuation coefficient of the optical fiber in the optical fiber link;
Loss of a single event (for example, an optical connector or bending), or total losses from end to
end on the fiber optic link;
Reflection amplitude (or reflection level) of an event, such as a connector.
5.1.2 The OTDR Curve Analysis
The OTDR analyzes the curve automatically.
Location of the curve:
Reflection event generated from connection and mechanical connector;
Non-reflection event (usually be fusion splice);
Optical fiber bundling: through scanning the first loss event that larger than the bundling
threshold, The OTDR detects the bundling of optical fiber;
Events list: Category of events, loss, reflection, and distance are listed through calculation.
5.2 Basic Principle of an OTDR
 OTDR stands for Optical Time Domain Reflectometer. The OTDR is an accurate optoelectronic
integrated OTDR. It relies on backward scattered lights that are generated from Rayleigh scattering
and Fresnel reflection when lights are transmitted in the optical fiber. It is widely used for the
maintenance, construction and monitoring of cable installations.
 Basic applications:
a) Measure the length of optical fiber and cable
b) Measure the distance between two points on optical fiber and cable
c) Locate faults and ruptures of optical fiber and cable
d) Display distribution curve of optical fiber and cable loss
e) Measure attenuation coefficient of optical fiber and cable
f) Measure loss between two points on optical fiber and cable
g) Measure loss of tie-ins
h) Measure reflection of reflection events of optical fiber and cable
Information related to length is gained through time. These back scattering signals indicates the
attenuation (loss/distance) degree caused by optical fiber. The curve formed is a downwards curve, which
reflects the transmission characteristics of the optical fiber.
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