A system that transmits light along the length of an optical fibre, a fine filament of glass or clear plastic. A flexible bundle of optical fibres joining an optical modulator to a remotely located optical demodulator can be used as a communications system. The modulator can be any source of visible or infrared radiation, often a light-emitting diode (LED) or semiconductor laser, which can be modulated by the signal to be transmitted; the signal can be digital or analogue. The demodulator consists of a photosensitive detector that converts the optically modulated signal back into an electrical signal at the receiving end. One of the advantages of a fibre-optics communications system is its very wide information bandwidth.