Fibre optics

A beam of light travels through a bundle of fibres and as long as the angle of incidence with the walls of a fibre is great enough it will be reflected along the fibre.

No cladding – multiple reflections at a fairly small angle. The cladding increases the critical angle between the two materials.
Critical angle for glass air interface with n = 1.55 = 41.8^o
Critical angle between glass (n =1.55) and glass (n = 1.45) = 69.3^o

Uses of Fibre Optics
1. Illuminating models or road signs using only one bulb
2. Endoscopy - seeing down inside a patient’s body
3. Communications – sending information along a light beam
4. Security fencing – very difficult to bypass
5. Fibre optic lamp