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.

[2] 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

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 This article incorporates public domain material from Federal Standard 1037C.