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Index of Refraction - DSP FTA Series

Its a value entered into the analyzer that will impact on the accuracy of the length measurement for fiber links.
The refractive index of a material is a measure of the speed of light in that material. It is defined as the ratio of the speed of light in a vacuum divided by the speed of light in the material. For glass this ratio is approximately 1.5 (300,000km/s divided by 200,000km/s).
        DSP FTA Index of Refraction
This value of 1.5 may be entered as a rough estimate of the refractive index, however, this may give inaccuracies of up to 2% in measured lengths. The following default values are programmed into the DSP-4x00 CableAnalyzer: 

  • 50/125 m Multimode 1.4725 @ 1300 nm 
  • 62.5/125 m Multimode - 1.4719 @ 1300 nm 
  • 9/125 m Singlemode 1.4719 @ 1300 nm 
More accurate figures for the refractive index of the fiber core may be obtained from the fiber manufacturer. However, graded index multimode fibers have a variation of refractive index across the core diameter, so the value to be used is what is known as the Group Index. The group index of a multimode fiber is a value for refractive index which represents the speed at which a pulse of light travels along the fiber, taking into account the graded index profile, etc.

Author: Adrian Young

Creation Date: 2014-02-27

Last Modified: 2014-02-27

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