Graded-index 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”

See also

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

References

• Federal Standard 1037C
• MIL-STD-188