A TYPICAL POINT TO POINT COMMUNICATION SYSTEM

A typical point to point communication system is shown in figure 

1. The analog information such as voice of telephone is converted into electrical signals in analog form and is coming out from the transmitter section of telephone.
2. The analog signal is converted into binary electrical signal using coder. The binary data comes out as a stream of electrical pulses from the coder.
3. These electrical pulses are converted into pulses of optical power by modulating the light emitted from a Light source like LED This unit is called an Optical transmitter.
4. Then optical signals are move into the optical fiber. Only those modes of light signals, which are move into the core within the acceptance angle, are sustained for propagation through the fiber by means of TIR. 
5. The optical signals from the other end of the fiber are move to the photo detector, where the signals are converted into binary electrical signals. 
6. Binary electrical signals directed to decoder to convert the stream of binary electrical signals into analog signal which will be the same information such as voice received by another telephone user. 

Note : As the optical signals propagating in the optical fiber are subjected to two types of degradation – attenuation and delay distortion. Attenuation is the reduction in the strength of the signal because of loss of optical power due to absorption, scattering of photons and leakage of light due to fiber bends. Delay distortion is the reduction in the quality of signal because of spreading of pulses with time. These effects cause continuous degradation of signal as light propagates and hence it may not possible to retrieve the information from the light signal. Therefore, a repeater is needed in the transmission path. An optical repeater consists of receiver, amplifier and transmitter.

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Encoding(coder) and Decoding(decoder) :

• Encoding means the creation of a messages (which you want to communicate with other person). On the other hand decoding means listener or audience of encoded message. So decoding means interpreting the meaning of the message.

Binary electrical signals :

• In most digital circuits, the signal can have two possible values; this is called a binary signal or logic signal. These correspond to the two values "zero" and "one" (or "false" and "true") of the Boolean domain, so at any given time a binary signal represents one binary digit (bit).

Optical siganal in pulse form :

• An optical pulse is a flash of light. Lasers and related devices have been found to have an amazing potential for generating light pulses with very special properties: There is a wide range of techniques for generating pulses with durations of nanoseconds, picoseconds, or even femtoseconds with lasers.

Light source :

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Optical fiber :

• An optical fiber is a flexible, transparent strand of very pure glass that acts as a light pipe to transmit light between two ends of the fiber. Optical fibers have a core surrounded by a cladding layer made of dielectric material. The optical signals in the core are confined by establishing a refractive index that is greater than the cladding.