Graded-index fiber

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In fiber optics, a graded-index or gradient-index fiber is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the fiber axis (the imaginary central axis running down the length of the fiber).

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 advantage of the graded-index fiber compared to multimode step-index fiber is the considerable decrease in modal dispersion.

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: “Characteristics of a 50/125 μm multimode graded index optical fiber cable”

[edit] See also

• Step-index profile
• Power-law index profile
• Gradient index optics

[edit] References

• Federal Standard 1037C
• MIL-STD-188