Fibre optic modal dispersion

In a fibre-optic cable, the light can be shone through at different angles.

If the light is shone at an angle closer to the normal, it will bounce more times, which means it will travel a further distance in total.

Knowing that , we know that if distance increases, the time taken will also increase.

Modal dispersion is when the light takes different lengths of time to arrive, depending on the angle it is shone through the cable at.

Solution

If we use very narrow fibres, the difference in distance between the different possible routes (angles) is smaller, so this becomes less of an issue.

In short, the solution is to use narrow fibres.