For optical fibers, a class of Graded-Index profiles characterized by the formula below, 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 ), is the Core radius, and g is a parameter that defines the shape of the profile.

Note 1: 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.