22 Oct 2017

Optical Fibers in Communication | All you need to know about Optical Fibers (Includes Video)

Here we will discuss all the Basics of optical fibers that include its Basic Introduction, Structure and Working Principle, Communication Process of optical fibers, Types of optical fibers, Benefits, Losses and Dispersion in optical fibers. We will discuss here each topic one by one-

Optical Fibers in Communication Video [HD]

 


1.What is an Optical Fiber?

An optical fiber is a flexible and transparent fiber which is made by drawing glass (silica) or plastic.
Optical fiber has a diameter slightly thicker than that of a human hair.

2.Structure and Working of the Optical Fiber

Optical fibers are made of glass or plastic.
Most optical fibers used in communication have diameter of 0.25 mm to 0.5 mm including outer coating.

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#OPTICAL FIBER SOURCES (DESIRABLE PROPERTIES)

Optical Fiber communication takes place between 0.8 micrometer to 1.7 micrometer of wavelength of electromagnetic spectrum.
Optical fibers have a transparent core which is surrounded by a transparent cladding and the cladding has a protective covering over it.
The image given below explains the concept of Total Internal Reflection (TIR) which is the phenomenon responsible for propagation of light inside the optical fiber.

Total Internal Reflection (TIR)  Phenomenon, TIR, Total Internal Reflection, optical fiber
Total Internal Reflection (TIR)
Phenomenon


Total Internal Reflection (TIR) Phenomenon, TIR, Total Internal Reflection, optical fiber
Total Internal Reflection (TIR)
Inside Optical Fiber

Based on the refractive index profile, there are two categories of optical fibers-
#Step Index Optical Fibers
#Graded Index Optical Fibers

In step index fibers, the refractive index profile makes a step change at the core-cladding interface.
In step index fiber if core has refractive index n1 and cladding has refractive index n2, then this condition holds-
n1>n2 
And this is necessary condition for Total Internal Reflection (TIR) in the optical fiber.
While the graded index fibers don't have a constant refractive index in the core but the refractive index of the core decreases with increasing radial distance from the core axis.

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#STEP INDEX OPTICAL FIBER (MULTIMODE AND SINGLE MODE STEP INDEX FIBERS)

It has maximum value of refractive index at the core axis that decreases as we move away from the core axis and becomes constant in the cladding.
The light rays travel inside the core by the phenomena of total internal reflection. Since the core has higher refractive index (n1) than that of cladding (n2), i.e. n1>n2.
So when the light rays fall on the core-cladding interface (moves from denser to rarer medium), it returns back into the core.
But for the Total Internal Reflection (TIR) to take place, it is necessary for the light rays to have incidence angle greater than the critical angle while moving from denser to rarer medium (core to cladding).

3.Optical Fiber Communication Process

Message that we want to transmit maybe non-electrical in nature (audio signal), so first of all it needs to be converted into electrical form using transducers.
Now the message converted into electrical form modulates an optical source. Ex. LASER or LED.

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#ADVANTAGES OF OPTICAL FIBER COMMUNICATION
#Step Index Vs Graded Index Fibers

After this the light rays containing message travel through the optical fiber by the phenomena of total internal reflection. Due to total internal reflection the energy loss is negligible inside the fiber while travelling.
Now at the receiving end, photodetectors like photodiodes or phototransistors etc., are used to convert the light signal back into electrical signal. Then the original message signal is retrieved from this electrical signal.

4.Types of Optical Fibers (Based on Modes of Propagation)

There are two types of optical fibers based on modes of propagation -
#Single Mode fibers (SMF)
#MultiMode fibers (MMF)
As clear by the name itself, the single mode fibers support only one propagation path, since they have very small diameter. While multimode fibers can support many propagation paths or transverse modes as they have larger diameter.
Single mode fibers are used for long distance communication while multimode fibers for short distance communication.
Single mode fiber provide greatest transmission bandwidth and lowest losses in communication.

5.Benefits of Optical Fibers

#Energy loss is negligible inside the optical fibers while propagation due to total internal reflection.
#Optical fibers provide very large potential bandwidth (since optical communication takes place at very high frequency (10^13-10^16).
#Optical fibres have small size, are lightweight and very flexible.

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#OPTICAL FIBER: STRUCTURE AND WORKING PRINCIPLE

#Optical fibers provide electrical isolation and are shock resistant. Since inside the fiber light propagates; not any electric current.
#Optical fibers provide high degree of signal security since these fibers do not radiate significantly unlike copper cables.
#Optical fibers are easy to maintain and the communication system is reliable.

6.Losses in Optical Fibers

Although the optical fibers have negligible losses in propagation but some losses are still present. These losses are the following-
#Material absorption
#Linear and nonlinear scattering
#Fibre bend losses


7.Dispersion in optical fibers

When light rays travel through the fiber, the phenomena of dispersion (broadening of transmitted light pulses), takes place. Because of this dispersion, each pulse broadens and overlaps with its neighboring pulses. Due to this, pulses become indistinguishable at the receiving end. This effect is known as Inter Symbol Interference (ISI).

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#Single-Mode Optical Fiber Advantages

The dispersion is of two types-
#Intermodal Dispersion
#Intramodal Dispersion
Here is the comparison of intermodal dispersion in different types of optical fibers- Multimode step index fiber> Multimode graded index fiber> Single mode step index fiber

Read More-

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ADVANTAGES AND DISADVANTAGES OF DIGITAL COMMUNICATION SYSTEM

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