EXFO IQS-3150 Variable Attenuator for IQS-500/600 - Manual (Page 72)

Measuring Multimode Insertion Loss
66 IQS-3150
There are several methods of eliminating these cladding modes:
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A cladding mode stripper (preferred method) is a material with a
refractive index greater than that of the cladding. With the cladding
exposed, the fiber is immersed in the mode stripper (glycerin, oil, or
other suitable liquid). Due to the greater refractive index of the stripper,
light energy is not reflected at the cladding-stripper interface and
passes through the stripper.
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Cladding modes attenuate to insignificant levels over relatively short
distances. Therefore, we recommend using a long fiber jumper.
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A mandrel wrap can be introduced by making a minimum of five turns
around a 0.5 in. diameter mandrel. This method will introduce slight
losses in the multimode core and remove some of the cladding modes.
A mandrel wrap is not the preferred method of controlling cladding
modes in multimode fibers.