Solution:

Leaky Modes:

This is the marginal case where a mode is borderline between being bound and being a cladding mode.

These modes have group velocities slower than the bound modes and so contribute to dispersion of the signal.

In some situations, system designers eliminate leaky modes by putting some tight bends into the fiber. The radius of the bend is chosen to pass all legally bound modes and to eliminate leaky ones. This is called “mode stripping”.