Fibre Optic Cable

A fibre optic cable propagate a signal as a pulse of light along a transparent medium.

A fibre optic cable is made from a glass or plastic core that carries light surrounded by glass cladding that (due to its lower refractive index) reflects "escaping" light back into the core, resulting in the light being guided along the fibre. The outside of the fibre is protected by cladding and may be further protected by additional layers of treated paper, PVC or metal. This required to protect the fibre from mechanical deformation and the ingress of water.

Fibre optic cable consisting of a core and cladding with different refractive indices in some cases fibre optic cables are strengthened by strengthening fibres or external protective wrapping.

Fibre optic cable used to transmit a serial bit stream using pulses of light (when the signal can take one of several paths it is called "multi-mode", whereas a single longidtudinal path is called "single mode").

Most 10 Mbps links operate using multimode fibre - typically 62.5 micrometres in diameter (50 micrometer cable is also used). For longer distance operation single mode fibre is prefered, but this increases the cost of the link.

Fibre optic cables are used in LANs where they offer specific advantages. They are increasingly replacing copper conductors in WANs and MANs because of their unique properties:

Fibre optic cables may also be used in LANs (e.g. 10BF) and are used to span larger distances, provide potential upgrade to higher data rates or to provide electrical isolation (e.g. when a cable must be laid between two buildings).


See also fibre support in:


Gorry Fairhurst - Date: 18/02/2012 EG3557