Fluke Networks CertiFiber Pro Users Manual - Manual (Page 373)

Chapter 15: Custom Media and Test Limits
About the Index of Refraction
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About the Index of Refraction
The index of refraction is the ratio of the speed of light in a
vacuum to the speed of light in a fiber. The tester uses the index
of refraction to calculate fiber length. When you increase the IOR
value, the calculated length decreases.
The default values the tester has for each fiber type are
satisfactory for most applications. Small differences between the
default IOR and the actual IOR of a fiber usually do not make
enough difference in length to make a fiber fail a test.
It is necessary to change the IOR at these times:
 The customer tells you to use a specific IOR value for the job.
 You test long fibers where a small difference between the
default and actual values of IOR makes an unacceptably large
error in length measurements.
 In some types of cable, some or all of the fibers are longer
than the cable jacket. This can occur because the fiber has a
spiral path inside the jacket. When you use and OTDR to
locate faults on these cables, the fault is closer to the OTDR
than the measured distance along the cable jacket. To make
the measured distance to the fault the same as the distance
along the cable jacket, adjust the IOR until the length of the
fiber is the same as the length of the jacket.
To change the IOR for a fiber, make a custom fiber type.