Optical fiber is made of very long thin flexible but solid glass or plastic fiber. The refractive index of the material of fiber is 1.7. A layer is made on this fiber by a material of comparatively less refractive index. When light ray that incidents at a small angle enters through one end of the fiber, then successive total internal reflections of light take place on the wall of the fiber and finally it emerges through the other end.

Light can be sent through the fiber almost without any loss of energy even if it is bent or coiled. A set of optical fiber is called optical tube.

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Uses of optical fiber in the field of health and telecommunication:

An optical tube is passed through the mouth to stomach in order to examine the inner wall of the stomach of any patient. A set of optical fiber of this optical tube is sent to lighten the stomach and the other set helps to see the lightened portion of stomach from the outside. This process is known as endoscopy. In this way by sending optical tube the block inside the artery, vein and function of valves of heart can be observed. Optical fiber is used for sending or receiving electrical signals from one place to another.

Before sending, the electrical signal has to be converted into optical signal. Near about 2000 telephone signals can be transmitted at a time through a single optical fiber. Almost no change takes place to the intensity of the signals for this kind of transmission. The use of optical fiber at present has brought about a significant change in communication system.