MBR5 User Manual
MBR5 Rev 007
25
Figure 12: Dual Display Mode
Termination Techniques
Termination is a term to describe the action of blocking all backreflection
beyond a point in a network of components. The termination technique varies
depending on the fiber type. There are two main termination techniques:
•
Mandrel wrap
consists of wrapping the fiber around a relatively small
mandrel, causing attenuation in the fiber which prevents any reflected light
after the mandrel from returning back to the meter. Mandrel wrapping is
used exclusively on single-‐mode fiber since mandrel wrapping does not
attenuate the lower order modes in multimode fiber (i.e. impossible to
attenuate all the light in a multimode fiber using a mandrel wrap).
•
Index-‐Matching Medium
allows the light to escape the fiber through the
end of the fiber (either bare fiber, or through a connector) with minimal
reflections back to the meter. An Index Matching medium can be used on
single-‐mode fiber if expected BR is not lower than -‐65dB (UPC connectors)
and multimode fiber, but since it is less effective than mandrel wrapping, it
is usually used on multimode fiber only. Remember that an index matching
medium cannot be used on single-‐mode fiber with APC connectors since
expected BR of such connectors is below -‐65dB.
Termination of the fiber is critical. Stable and repeatable backreflection
measurements will only be achieved with stable and repeatable termination of
the fiber.
Mandrel Wrap Technique (for Single-‐mode Fiber)
As mentioned above, termination of single-‐mode fiber is most of the time
performed by mandrel wrapping. Remember however that the index-‐matching
technique described below could also be used for single-‐mode fiber with UPC
connectors.
High-‐attenuation bends in the fiber (bends with a relatively small radius)
remove all backreflection and can be made anywhere along the length of the
cable. Typical mandrel diameters will be as follow:
•
13mm for 1490, 1550, 1625 and 1650 nm
•
9mm for 1310 nm with SMF-‐28 fiber
•
7mm for 1310 nm with low bend sensitive SMF.
BR = -XX.XdB 1310
IL = X.XdB 1
DUAL DISPLAY
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