Power-law index profile

For optical fibers, a power-law index profile is an index of refraction profile characterized by

:where$Delta\; =\; \{n\_1^2\; -\; n\_2^2\; over\; 2\; n\_1^2\},$

and $n(r)$ 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 cladding, which is taken to be homogeneous ($n(r)=n\_2\; mathrm\{\; for\; \}\; r\; ge\; alpha$), $alpha$ is the core radius, and $g$ is a parameter that defines the shape of the profile. $alpha$ is often used in place of $g$. Hence, this is sometimes called an alpha profile.

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. In the limit of infinite $g$, the profile becomes a step-index profile.

ee also

*Graded-index fiber

References

*Federal Standard 1037C