Define the graded index multimode fibers intermodal dispersion specifically.

In graded index fibers, the index of the core material slowly raises and turns into maximise at the centre of the core. Hence the rays that travel off-axis by the core travels via regions of lower refractive index and therefore speeds up and at last catches up periodically along with the rays traveling axially. It decreases the intermodal dispersion by the typical value of 75ns/km.nm for a SI-MM fiber to approx 35ns/km.nm for such graded index multimode fiber.

Graded index multimode fiber (GI-MM fiber)