OPTICAL COMMUNICATION

Optical communication:

          Nowadays Optical communication is finding more and more application in communication. Indeed, worldwide telephone network is optic based. Optical communication is a telecommunication system, in which information are carried by light pulses from one place to another through an optical fiber, which act as a waveguide. They are used to transmit  cable television signals, internet communication WANs, etc. To know more about optical communication system we should know about optical fiber.

Optical fibers:

                                                                             

   Optical fiber is thin and flexible, which is made up of fiber ,transparent dielectrics or glass. lt consists of outermost cladding and innermost core and the core is  surrounded by cladding. Over cladding, two more coatings are provided which protects the optical fiber from outer environmental changes. It was first successfully developed in 1970 by Corning Glass works.

Principle:

         The principle by which the light travels inside the optical fiber is total internal reflection. To achieve total internal reflection ,the light should travel from denser medium to rarer medium and the angle of incidence should be greater than the critical angle.     

                             
•The maximum angle of incidence for which the light entered through the fiber can suffer total internal reflection is called acceptance angle of the fiber.
•The sine of the acceptance angle of the fiber is called numerical aperture.           

Block Diagram:       

                             

Working:

            Input such as sound or video is fed into the transducer which convert these into electrical signals. These electrical signals are converted into proper format by a modulator. Carrier source generates the light wave called carrier, on which the electrical signal is transmitted. The most Commonly used carrier source is Laser diode or Light emitting diode. This light wave is collimated by the channel coupler which is a lens. Coupler feeds the power into information channel. A glass or plastic fiber is the channel. Important characteristics of the channel are low attenuation and large light acceptance cone angle. A signal propagation along a fiber normally contains a range of fiber optic frequencies and divides its power along several ray paths. This results in the distortion of the propagation signal.  Photo detector converts optic wave into an electric current. Developed current is proportional to the power in the incident optic wave. Output current contains the transmitted information. Signals are processed by filtering and amplification. The bit error rate(BET) should be very small for quality communication. Finally, the message from the signal processor in electrical form is transformed into corresponding input information.     

Advantages:

•Signals can be transmitted into large distances.

•Extremely high bandwidth.

•Small in size and light in weight.

•Resistence to electro magnetic interference.

Disadvantages:

•Light will be attenuated and dispersed when transmission distance are much longer. This requires        the addition of extra optical components like EDFA.

•Cost is higher than copper cable.

•More fragile than electrical wires.