Principle- It is based upon total internal reflection.
Construction- Optical Fibres consists of thousands of extremely thin and long strands of high-quality glass/quartz. A strand may have a diameter of nearly 1 micrometer (10-6 m). The optical fibres are coated with a thin layer of material of lower refractive index. The refractive index of the main fibre is nearly 1.7. The refractive index of coating is nearly 1.5.
Transmission of Light- Consider light to be incident on one end of the fibre at i>c. The light undergoes repeated total internal reflections along the fibre. The light finally comes out of the other end of the fibre. The optical fibres can transmit light from one end to the other end due to repeated total internal reflections even if the fibre is bent or twisted.
Two Special Advantages- (1) Optical Fibres can be twisted in any form. (2) There is very little absorption of light and almost the whole of the light is transmitted from one end to the other end.
Uses: (1) Optical Fibres are used to transmit light without any loss in its intensity over distances of several Kms. (2) Optical Fibres are used in the manufacture of medical instruments like endoscopes. (3) Optical Fibres are used to transmit the image of the objects. (4) Optical Fibres are used to transmit electric signals from one place to another place. The electrical signals are converted into light signals by transducers. Then these light signals are transmitted through optical fibres to distant places. (5) They are used in telecommunication for transmitting signals.
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