Power-law index profile
For optical fibers, a
power-law index profile is a class of graded-index profiles characterized by where
n (
r ) is the nominal
refractive index as a function of distance from the fiber axis,
n 1 is the nominal refractive index on axis,
n 2 is the refractive index of the homogeneous cladding (
n (
r ) =
n 2 when
r ≥ α), α is the
core radius, and
g is a parameter that defines the shape of the profile.
Note 1: α is often used in place of g . Hence, this is sometimes called an alpha profile.
Note 2: For this class of profiles, multimode distortion is smallest when g takes a particular value depending on the material used. For most materials, this optimum value is approximately 2. When g increases without limit, the profile tends to a step-index profile.
Source: from Federal Standard 1037C