**3.2 Fiber optic cable**

A fiber-optic cable is made from fine hair-like glass fiber, which carries light impulses that are transmitted by an LED or a laser source. Data in optical fiber are transmitted in the form of light (**Figure 5**).

Consider a long and flexible pipe, with its insides perfectly coated with silver halide, such that the inside is all a mirror. It is like a cylindrical mirror from inside. When you flash a source of light (a laser or may be a torch), what do you see at the other end? The light will reach the other end, regardless of whether the pipe is straight, curved, or twisted. Is not it? Yes, it will. This is because light will reflect off the sides of the flexible tube at all angles with almost negligible losses. But mirror tubes would be too bulky to handle. Thus, optical fibers are used to serve the purpose. Optical fibers are such flexible pipes made of glass instead of mirrors. It employs the principle of total internal reflection to transmit light from one to the other end.

Glass is amazingly pure; light can make it through even if it is several miles long. The glass for an optical fiber is drawn into an extremely thin strand, with a thickness comparable to that of a human hair. The glass strand is then coated in two layers of plastic.
