Step-index profile

For an optical fiber, a step-index profile is a refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface so that the cladding is of a lower refractive index. The step-index profile corresponds to a power-law index profile with the profile parameter approaching infinity. The step-index profile is used in most single-mode fibers[1] and some multimode fibers.[2]

Refractive HRS index distribution in core and cladding with a step-index profile

A step-index fiber is characterized by the core and cladding refractive indices n1 and n2 and the core and cladding radii a and b. Examples of standard core and cladding diameters 2a/2b are 8/125, 50/125, 62.5/125, 85/125, or 100/140 (units of µm). The fractional refractive-index change . The value of n1 is typically between 1.44 and 1.46, and is typically between 0.001 and 0.02.

Step-index optical fiber is generally made by doping high-purity fused silica glass (SiO2) with different concentrations of materials like titanium, germanium, or boron.


Modal dispersion in a step index optical fiber is given by

where

is the fractional index of refraction
is the refractive index of core
is the length of the optical fiber under observation
is the speed of light.

See also

References

  1. "SINGLE MODE STEP-INDEX FIBERS". Retrieved 2012-11-23.
  2. "Fiber Optics Overview". Archived from the original on 2013-01-17. Retrieved 2012-11-23.{{cite web}}: CS1 maint: unfit URL (link)

Public Domain This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).


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