Uses of optical fibres

Do you know why the phone signal gets weaker during the rain sometimes and we are not able to call or use the internet connection? This is because our phones communicate by transmitting the electromagnetic waves through the networks on the antennas which are called base stations. Due to the rain this communication is disturbed and we are not able to use the services. Is there any solution for this problem? Yes, if we use the optical fibre for transmitting the signal then the outside condition will not affect the communication. Let's see what optical fibre is !

Table of content

What is optical fibre?
Working principle of optical fibre
Types of optical fibre
Uses of optical fibre
Practice problem
FAQs

What is optical fibre?

Optical fibre is a hair-like flexible and transparent fibre which is used for the transmission of data signals over large distances with a higher speed. Hence optical fibre is used to provide the service of internet, telephone and television etc. Optical fibre works on the principle of total internal reflection.

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The optical fibre is made of various glass and plastic materials. Basically the optical fibre is consist of the following components-

Core - Core is a thin glass tube situated at the centre of the fibre. This is the place where the light is transmitted.
Cladding - The core is surrounded by a layer which has a lower refractive index, known as cladding. During the single transmission it is responsible for reflecting the signal back to the core.
Plasting coating - It is provided at the outer surface as structural cladding to protect the internal component of the fibre.

Working principle of optical fibre

As discussed above, the optical fibre works on the principle of total internal reflection. When a light beam travels in an optically denser medium and reaches the boundary it gets refracted with a larger angle than the angle of incidence (case 1). Now if we increase the angle of incidence the refractive angle will also increase (case 2). When we reach a maximum angle at which the refractive ray grazes parallel to the boundary (case 3). This angle is called the critical angle (i_c). If we incident a ray on the boundary inside the denser medium, at an angle greater than the critical angle then it reflects back to the same medium (case 4). It is called the total internal reflection of light.

This phenomenon of total internal reflection is used to transmit the light through an optical fibre. As the core has a higher refractive index than that of the cladding, light signals continuously strike on the boundary of the core at an angle equal to or greater than the critical angles and then the cladding reflects it back to the core. This process goes on along the entire distance of signal transmission.

A fibre optics system consist of the following components

The transmitter - The transmitter creates the light signal, decodes them and sends them to the optical fibre.
The optical fibre - The optical fibre transmits the signal from one place to the other place.
The receiver - It receives the transmitted signal and encodes it to the user desired form.
The optical regenerator - It is used to amplify the signal. It is used when the data is to be transmitted by a long distance.

Types of optical fibre

The optical fibre is classified based on the various parameters like material used, refractive index of the material and the propagation of light.

Based on material used

Glass and plastic are mostly used for the manufacturing of the optical fibre.

Glass fibre - Core of the glass fibres is made of glass.
Plastic optical fibre - In plastic fibre polymethylmethacrylate (PMMA) is used as a core material.

Based on refractive index

The classification is as follows -

Step index fibre - In step index fibre, there is a separate core and cladding. There is a boundary. Core has a constant refractive index which is greater than the refractive index of cladding.

Graded index fibre - In this fibre the core and cladding is made of the same material having a variable refractive index which is greater at the centre and lower at the outer surface. Thus, the outer surface of this fibre works as the cladding. There is no distinct boundary between the core and the cladding.

Based on the propagation of light

Based on the propagation of light, optical fibre can also be classified as

Single mode fibre - Single mode fibres used to transmit the signal for a long distance.
Multi mode fibre - multimode fibre is used for short distance transmission.

Uses of optical fibre

The optical fibre is used in various industries and medical applications as -

Medical industry - As optical fibre is very thin and flexible so it is used to view the internal part of the body. It is also used to transmit light on the interior during surgeries. Optical fibre is helpful in the dentistry application also.
Communication - Optical fibre is mainly used for telecommunication purposes. Compared to the copper wires, it transmits the signal more accurately and with greater speed. As optical fibre is made of plastic and glass, it is light in weight and more flexible hence easy to handle.
Defence - As we all know, in defence the security of data is more important. The optical fibre is best for this as it reduces the risk of data leakage to unwanted entities.
Internet - As the optical fibre can carry large amounts of data with very high speed so it can be used in providing the internet.
Computer networking - If we use optical fibre to connect the different computers in the same building, the communication between them is greatly enhanced.
Automobile industry - The modern automobile vehicle has different parts and it is controlled by ECU. There is a need to establish a fast communication system between them. The optical fibre is best suited for this purpose. It increases the safety and security of the vehicle.
Lighting and decoration - As the optical fibre is made of transparent materials so it can also lighten the area. Because of this it is widely used for decoration purposes.

Practice problems

Q1. What are the various advantages of optical fibre ?

A. Some of the advantages of using optical fibres are given below

Optical fibre is lesser in weight
It has minimum losses so less power consumption.
Having a very low cost for the longer run.
Optical fibre secure and keep the data private.
It has large data transmitting capacity.
There is no sparking or chance accident from this.
No harmful electromagnetic radiation emitted from optical fibre.

Q2. Write various disadvantages of the optical fibre?

A. The disadvantages of optical fibre are

The installation of cable is very expensive.
It is difficult to connect two optical fibres which may lose some percentage of light beam.
For analysing the transmission of light in the fibre optic, special devices are required.
Skilled people or engineers are needed to deal with the optical fibre.

Q3. Write the difference between step index optical fibre and Graded index optical fibre?

A. The step index optical fibre has a separate core and cladding, core has greater refractive index than the cladding while the graded index optical fibre is made of single material with varying refractive index.

Q4. What are the factors that reduce the optical power during transmission?

A. In signal transmission there are few things which reduce the power of the signal. They are the absorption, scattering and the waveguide effect.

FAQs

Q1. What is the speed of data transfer in optical fibre?
A. The speed of optical fibre is 1.6 Tb/s for field deployed systems and 10 Tb/s in lab systems.

Q2. What is the value of general loss in optical fibre?
A. The value loss is generally less than 0.3 db/km.

Q3. What bandwidth does the optical fibre have?
A. The optical fibre has the bandwidth 900 THz.

Q4. On which optical principle does the optical fibre work?
A. The optical fibre basically works on the principle of total internal reflection.