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IM AQ1210-01EN
Near-end Reflection
This is the reflection that occurs at the point where the instrument and the optical fiber cable are
connected. This also includes the instrument’s internal reflection. In the section where this near-end
reflection is detected, even if there are other connections, the loss and reflections that occur at these
points cannot be detected. This section is the near-end dead zone.
When you are measuring a short distance, connect a launch fiber cable to reduce the effect of the
near-end reflection.
Backscatter
When light travels through an optical fiber cable, Rayleigh scattering caused by changes in the density
of materials that are smaller than the light’s wavelength and inconsistencies in the fiber's composition
generates loss in the optical fiber itself. The portion of the scattered light that travels in the direction
opposite to the direction of propagation is known as backscatter.
Small
material
Incident ray
Backscatter
Optical fiber cable
Splice Loss
Because spliced sections of optical fiber cables have a great number of changes in the material’s
density and inconsistencies in the cable’s composition, loss due to Rayleigh scattering becomes large,
and splice loss occurs in these sections.
Reflection at the Connection Point of Connectors
Using a connector to connect two optical fibers is different from splicing them together in that a small
gap remains between the two fibers. Because this gap has a different index of refraction, reflection
occurs.
Optical fiber cable
Optical fiber cable
Connector
Gap
Fresnel Reflection at the Open End of the Fiber
This is the reflection that occurs at locations where the index of refraction changes (glass to air) such
as where there are tears in the optical fiber cable or at the end of it. When the optical fiber cable end
face is vertical, approximately 3% of the incident optical power (14.7 dB) is reflected.
Glass Air
Incident ray (100%)
Reflected light (3%)
Light (97%)
1.3 Displaying Measured Data (OTDR)
