HOW TO SEND 25000 PHONE CALLS IN A HAIR THIN WIRE?

In a land line, voice is converted into electrical signals by a microphone and sent through wire. The sound is reproduced by the speaker at the other end. Now we have modern technology called fiber optics. Here voice or digital data is first converted into electrical signals and then into light signals(laser or infra red) using electronic element. It is then sent through glass fibers (strands).

We know, electric current flows through metal wire because electrons are pulled by voltage difference. But how the light will travel through glass fibers without oozing out? Imagine long narrow hall way. Its walls fitted with mirrors. Hallway goes zig-zag. If you send a torch light beam to a mirrored wall, it will reflect and re-reflect on the walls again and again and travel trough the hallway. Similarly, laser beam travels through glass strands using 'total internal reflections'.

Total internal reflection: If a ray of light goes from glass to air and if the angle of incidence on the wall of the glass is more than 42 degree (with the vertical), the ray will only reflect inside the glass and can not escape into the air. Thanks to this phenomenon, that is why diamond glitters.

Digital data (0s,1s) is converted into Laser pulses and travel through glass strands nearly at the speed of light. One can send several light rays or signals through single glass strand. These optical fibers can carry 100 mega bits per second. Internet will be faster in the near future. Already video calls are reality. In future, we will be able to transmit 3D holographic images. Hence a communication and entertainment revolution is just around the corner. A bunch of glass fibers will be able to carry several million phone calls.

'Lights on ' inside the body:
A dentist light up the inside the mouth using optical fiber. A doctor can see inside the throat or stomach using this optical fiber and it is called endoscopy.
One can also inspect mechanical parts with this fibers.

Why optical fiber is superior than copper wire?
1. Less expensive
2. Thinner
3. Higher carrying capacity
4. less signal degradation
5. light signals
6. low power
7. digital signals
8. Non-flammable
optical fiber is yet another important discovery by mankind.
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