Optical fibre communication
We use electrical signals for the transfer of information from one place to another. For long distance communication we use radio waves. But one of the disadvantages of these communication methods is that there will be unwanted noise present in the received signal of these transmitters and also the speed of transmission. Also the intercontinental communication which covers 1000 of Kilometers is not possible via Electrical transfer of data. In order to make this possible we have adopted a new medium of communication. This is called the Optical fiber communication.
One of the main advantage of using light as a medium of transfer of information is that the interference due to noise will not be present and the speed of light can be used for faster data transfer. Optical fibers are glass rods with a low density plastic wrapping or covering. The basic principle of optical fiber communication is the multiple reflection or refraction.
Terms related to optical fibre communication
Refraction: - The bending of light wave when entering from one medium to another depends on their refractive index. This bending is called refraction. When light enter from denser to lighter medium light moves away from normal. When light enter to denser medium from lighter medium light moves towards the normal.
Reflection: - The coming back of light when entering from one medium to another is called reflection. If all the rays of light are reflected back then it is called total internal reflection. If some of the rays are reflected then it is called partial reflection.
Total internal reflection: - The complete reflection of incident light is called total internal reflection. Total internal reflection takes place only when light enters from denser to lighter medium.
Critical angle: - The angle at which the angle of refraction become 90 degree.
According to Snell’s law the light entering from denser medium to lighter medium with angle of incidence equal to critical angle, light will undergo total internal reflection. This is the technique used in optical fibre communication, the material used in optical fibre is arranged such that the light entering in to the fibre undergoes multiple internal reflections and the light entering at one end will reach the other end. The below figure show the constructional features of optical fibre cable.
It consists of a core which is made up of denser medium and a cladding surrounding it which has lighter medium. Light which is to be transmitted is allowed to fall into the core. Light enters from core to cladding undergoes multiple internal reflection and light travels through the cable. The cable should be arranged such that the angle of incidence of light must be at critical angle or larger than critical angle. There should not be any large bends in the cable which makes the angle of incidents lesser than critical angle. Otherwise total internal refection will not take place.
Advantages of optical fibre communication
The interference of other signals like noise will be absent in optical fibre communication. Maximum accuracy can be attained for data transmission. Large distance transmission is possible. Power required for transmission is less when compared to other channels of communication.
But the disadvantage of using optical fibre is that the cost of setup of the devices is large. Also the repairing cost is large.
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