It is based on the principle of total internal reflection. This means light that is travelling thru the core hits the outside surface at an angle of incidence greater than the critical angle for that material, so that all the light is reflected back into the fibre without loss. To stop light scattering the core is clad with a glass of a much lower refractive index.
Fibre optics is used in many different areas of society.
In medicine it takes the form of an endoscope. …
