Explain principle, construction and working of optical fibre.

Explanation

Optical fibres too make use of the phenomenon of total internal reflection.
Optical fibres are fabricated with high quality composite glass/quartz fibres. Each fibre consists of a core and cladding.
The refractive index of the material of the core is higher than that of the cladding.
Function: When a signal in the form of light is directed at one end of the fibre at a suitable angle, it undergoes repeated total internal reflections along the length of the fibre and finally comes out at the other end.

Since light undergoes total internal reflection at each stage, there is no appreciable loss in the intensity of the light signal.
Optical fibres are fabricated such that light reflected at one side of inner surface strikes the other at an angle larger than the critical angle.
Even if the fibre is bent, light can easily travel along its length. Thus, an optical fibre can be used to act as an optical pipe.
A bundle of optical fibres can be put to several uses.
The device which converts one form of energy in another form is called tranducer.
Optical fibres are extensively used for transmittin and receiving electrical signals which are converted to light by suitable tranducers.
Obviously, optical fibres can also be used fo transmission of optical signals. For example these are used as a .light pipe. to facilitate visua examination of internal organs like esophagus stomach and intestines.
Decorative lamp with fine plastic fibres with their free ends forming a fountain like structure. The other end of the fibres is fixed over an electric lamp.
When the lamp is switched on, the light travels from the bottom of each fibre and appears at the tip of its free end as a dot of light.
The fibres is such decorative lamps are optical fibres.
The main requirement in fabricating optical fibres is that there should be very little absorption of light as it travels for long distances inside them. This has been achieved by purification and special preparation of materials such as quartz.
In silica glass fibres it is possible to transmit more than 95 % of the light over a fibre length of 1 km.