Because parts of the core closer to the fiber axis have a higher refractive index than the parts near the cladding, light rays follow sinusoidal paths down the fiber. The most common refractive index profile for a graded-index fiber is very nearly parabolic. The parabolic profile results in continual refocusing of the rays in the core, and minimizes modal dispersion.
This type of fiber is normalized by the International Telecommunications Union ITU-T at recommendation G.651.1.
Pulse dispersion in a graded index optical fiber is given by
is the difference in refractive indices of core and cladding,
is the refractive index of the cladding,
is the length of the fiber taken for observing the pulse dispersion,
is the speed of light, and
is the constant of graded index profile.
- This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
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