FHO5000
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2.4 Fundamental of OTDR
OTDR——Optical Time Domain Reflector is a high precision optical testing meter that use the theory of Rayleigh
scattering and Fresnel reflection. It is widely used in the maintenance, construction and monitoring of an optical line. All the
important parameters like fiber length, optical loss, connection loss, broken or twisted point and etc. of a fiber can be shown
on the OTDR. When the a light transmits along a fiber, it would be scattered to various directions caused by the difference of
come properties of the transmission medium, this phenomenon called Rayleigh scattering. During the scattering process,
some of the light will be scattered along the absolutely converse direction, this phenomenon is called Rayleigh back-
scattering. It provides some details about the fiber length. The parameters about fiber length can be got by calculation with
the parameter of time(This is the derivation of TD in OTDR——Time Domain optical Time Domain Reflectormeter).
These back-scattering signals shows the loss level of a fiber and through these information, OTDR can generates a
backward oblique trace which reflects several important attributes of a optical fiber. When the light, transmitting downward
along the fiber, meet a different density medium, a part of the light will be reflected, this phenomenon is called Fresnel
reflection. There are many reasons can cause the changing of the medium density like a little slot at the splicing point, a
broken of fiber or etc. This phenomenon is usually used to locate the discontinuous point. Compare to the Rayleigh
scattering, the consuming amount of the light in Fresnel reflection is much more then it is in Rayleigh scattering. The power of
Fresnel reflection is tens of thousands times to the back-scattering's. The reflection level depends on the changing grade of
refraction ratio.
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