In this fiber we grade the refractive index profile of the core and consequently it is called the graded index fiber.
A graded index fiber and the ray propagation is shown in the figure 6:
Figure (6): (Graded Index Profile)
(c)
If we taper the profile optimally, we get the dispersion reduction compared to that for a step index fiber, even by a
factor of thousand. The data rate of a typical graded index fiber is typically 10 to 100 times higher compared to a step index fiber.
Therefore, in practice, even for LANs, we use GIF (Graded Index Fiber) instead of SIF (Step Index Fiber).
3.
SINGLE MODE OPTICAL FIBER
The light basically consists of wave fronts. A line perpendicular to a wave front is called the ray. Light is an electromagnetic wave and when we say it travels like a ray it is a collection of wavefronts which move.
Let us take an optical fiber with light rays propagating in it. The rays and the wave fronts which are perpendicular to the rays, are as shown in figure 7:
