It is a thin, cylindrical cable made of glass fibre used for transmitting light signals. Light is propagated down an optical fibre by refraction and internal reflection. There are two types of fibres, one in which the central core has uniform refractive index and the other where there is a gradual change in the refractive index decreasing outward from the centre of the fibre. The core of an optical fibre is surrounded by a layer called the ‘cladding’ which has a uniform refractive index but of magnitude less than that of the core. The outside of an optical fibre is generally coated with a dark coloured plastic sleeving which protects the fibre.
Before they are sent through an optical fibre, electrical signals are converted into pulses of light by semiconductor devices known as light emitting diode (LED) and laser diode. At the far end, light is reconverted into electrical signals by a receiver which consists of a photodiode. Signals can be transmitted in both directions provided that both ends of the fibre have a source and a receiver.
The main advantages of optical fibres in transmission of information are its larger channel capacity, lighter weight compared to copper cables and no possibility of a cross talk between adjacent cables. Besides, these cables do not pick up any noise signals and can withstand extreme environmental conditions. They are even cheaper than copper cables.
