Solution:

Cladding Modes:

When light enters the fiber it is inevitable that some will enter the cladding. Also, when there are bends in the fiber or imperfections in the core-cladding interface then the light may leave the core and enter the cladding.

There are many possible modes that light may take in the cladding. Generally, these will leave the cladding (and the fiber) relatively quickly but some may propagate for a considerable distance. These modes will add significantly to dispersion and so it is generally desirable to get rid of them.

The principal way of ridding the fiber of unwanted cladding modes is to ensure that the refractive index of the plastic coating on the fiber is higher than that of the cladding. This minimizes the reflection between the cladding and coating and minimizes guidance at the cladding-coating interface.