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Step-index profile

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Refractive index profile in optical fibre
Refractive HRS index distribution in core and cladding with a 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 and some multimode fibers.

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 Ξm). The fractional refractive-index change △ = n 1 − n 2 n 1 ≪   1 {\displaystyle \triangle \,={\frac {n_{1}-n_{2}}{n_{1}}}\ll \ 1} . The value of n1 is typically between 1.44 and 1.46, and △ {\displaystyle \triangle } 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

pulse dispersion = △   n 1   ℓ c {\displaystyle {\text{pulse dispersion}}={\frac {\triangle \ n_{1}\ \ell }{c}}\,\!}

where

△ {\displaystyle \triangle \,\!} is the fractional index of refraction
n 1 {\displaystyle n_{1}\,\!} is the refractive index of core
ℓ {\displaystyle \ell \,\!} is the length of the optical fiber under observation
c {\displaystyle c} 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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