Fibre optic material dispersion

The different wavelengths of light and other electromagnetic waves have speeds that vary very slightly.

Red light, for example, travels slightly faster than blue light.

While usually this wouldn’t be an issue, in fibre-optic cables, light is often sent over long distances. We don’t want different components of the light arriving at different times!

This is often called pulse broadening.

Why not send white light?

White light is made up of all the colours. If we sent white light down a fibre-optic cable, then we actually send multiple differnent wavelengths which will arrive at different times.

Solution

We can solve this problem by sending monochromatic light (only one wavelength) instead of white light.