We all know that electricity travels from one place to another through metallic wires. Can light travel through wires too?
Light can also travel through wires, but these wires are not made of metals. They are made of glass or plastics. Light carrying wires are extremely thin and are called optical fibres. The branch of science dealing with the conduction and study of light through fibres is called Fibre Optics.
In 1870, a British physicist John Tyndal showed that light can travel along a curved rod of glass or transparent plastic. Light travels through transparent rods by the process of total internal reflection. The sides of the fibre reflect the light and keep it inside as the fibre bends and turns.
The narrow fibres have a thin core of glass of high refractive index surrounded by a thin cladding of another glass of lower refractive index. The core carries light and the covering helps bend the light back to the core.
Fibres are drawn from thick glass rods in a special furnace. The glass rod of higher refractive index is inserted in a tubing of glass of lower refractive index. Then the two are lowered carefully and slowly through a vertical furnace and the fibre drawn from the lower end is wound on a revolving drum. With this method, fibres of about .025 mm in diameter can be drawn.
Fibres so prepared have to be aligned properly in the form of a bundle. They should not cross each other; otherwise the image transported by it will be scrambled. They are kept in straight lines. Once the aligned bundle is made, it can be bent or turned in any desired direction.
There are many uses of fibre bundles. Physicians use instruments with fibre bundles to examine body cavities and the inner part of hollow organs by sending light from an external lamp. These instruments are known as fibre-scope. By introducing the bundle into the stomach or bladder, photographs can be taken of the internal organs.
Fibre optic devices can transmit television programmes and telephone conversations. In future, using laser beams and single bundle of optical fibres, scientists would be able to send thousands of telephone conversation simultaneously. Many developed countries have installed telephone exchanges using fibre optic cables. The use of optical fibres in video text, videophones and computer networks is increasing day by day.