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Optical Fibres
A glass fibre that functions as a waveguide for light. They are used in medical instruments (called fibrescopes) to examine internal organs (stomach, bladder, uterus, etc.). They are also used in short-range telecommunications.

Optical fibres consist of a glass core region that is surrounded by glass cladding. The core region has a larger refractive index than the cladding, so that the light is confined to that region as it propagates along the fibre. Fibre core diameters range between 1 and 100 micrometres, while cladding diameters are between 100 and 300 micrometres.

The step-index fibre consists of a glass core with a coaxial glass or plastic cladding of lower refractive index so that total internal reflection takes place at the interface between the core and the cladding.

In graded-index fibres, the fibre is stuctured, each layer of glass having a lower refractive index than the one inside it.