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 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 ''n
1'' and ''n
2'' 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
. n
1 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 (SiO
2) with different concentrations of materials like titanium, germanium, or boron.
See also
★
Graded-index fiber
★
Critical Angle
★
Numerical aperture
References
★
Federal Standard 1037C
★
MIL-STD-188