Two-fibre fibre optic cable, c 1950s.
© Science Museum / Science & Society Picture Library
Optical fibres can reflect light of all wavelengths. This experimental cable contains two optical fibres. Each one has a glas core surrounded by a cladding of resin which has a lower refractive index than the glas. The interface between core and cladding acts as a cylindrical mirror causing total internal reflection of the transmitted light. This enables a beam of light to travel through the fibre without escaping. Although the theory behind fibre optics was worked out by early scientists, most of the development in this field has taken place since the 1950s. Emphasis has been placed on making optical fibres les expensive and better carriers of light.