# Classification of Optical Fibers

On the basis of refractive index profile, we can classify optical fibers into two types-

# What is Step Index Optical Fiber

Step index fibers are the optical fibers, that have some constant value of refractive index in the core and some other constant value in the cladding.

## Step Index Fibers (Mathematical Representation)

n(r) = n1      ;   r<=a (Core)
Here n1>n2

Here n1 is refractive index of the core and n2 is refractive index of the cladding
'a' is radius of the core

## Classification of Step Index Fibers (Based on Modes of Propagation)

#Multimode step index fibers
#Single mode step index fibers

Here in this post we will see images, that will show you, how the light rays travel inside the core of the optical fiber, in case of both multimode step index fiber and single mode step index fiber. The images also show plots. These plots tell, how the refractive index of the core and cladding changes, as we move away from the axis of the core, in both types of step index fibres.

#OPTICAL FIBER (STRUCTURE AND WORKING PRINCIPLE)
Now let's observe the Plots and Working Structures of both Multimode and Single Mode Step Index Fibers one by one-

## Multimode Step Index Fiber

(Click the image to enlarge)

 Multimode step index optical fiber (structure and plot)

Since the diameter of the multimode step index fiber is large (>50 micrometre), therefore it can support multiple modes of light. Therefore it is known as multimode step index fiber. As you can see in the image above, that refractive index of the core is n1 and that of cladding is n2. Since it is the step index fiber, therefore the refractive index of the core is constant (n1), and does not change as we move away from the axis of the core, within the core. But as we reach to the core-cladding interface, the refractive index inside the cladding changes suddenly to n2.
Since it makes sudden (step) change in the refractive index at the core-cladding interface. This is the reason, why it is called as step index fiber and as it supports multiple modes, so called as multimode step index fibre.

#OPTICAL FIBER SOURCES (DESIRABLE PROPERTIES)

Since refractive index of the core (n1) is more than the refractive index of the cladding (n2), therefore Total Internal Reflection (TIR) phenomenon takes place, as the light rays move from the denser medium to the rarer medium (core to cladding).

## Single Mode Step Index Fiber

(Click the image to enlarge)

 Single mode step index optical fiber (Structure and plot)

It is also a step index fiber, but due to its small diameter of the core (2-10 micrometre), it can support only single mode of light. Therefore this type of step index fiber is known as single mode step index fiber. You can see the image shown above, how a single mode of light is propagating through the core of The Optical Fiber. Since it is a type of step index fiber,  therefore the refractive index of this optical fiber makes step (sudden) change at the core cladding interface. It is also clear from the plot given for the single mode step index fiber. Observe the plot shown in the image, how the refractive index of the fiber changes at the core- cladding interface from denser medium n1 (core) to rarer medium n2 (cladding).

## Comparison of Multimode Step Index Fibers and Single Mode Step Index Fibers

1.Diameter
Multimode step index fiber has larger diameter of the core (>50 micrometer).

Single mode step index fiber has smaller diameter (2-10 micrometres)

2.Number of Modes
Propagation of multiple modes is possible in case of Multimode step index fiber.

Only single mode is present in single mode step index fiber.

3.Dispersion
Dispersion is high in case of Multimode step index fiber, due to differing group velocities of various modes.

Dispersion is low, which is due to broadening of the single pulse of the light in case of single mode step index fiber.

4.Bandwidth
Bandwidth is low multimode step index fiber.
Bandwidth is higher in single mode step index fiber.

5.Coupling
In case of multimode step index fibers, spatially incoherent optical sources (LEDs), can be coupled easily and efficiently due to its large diameter.  Due to large numerical aperture (NA), easy coupling is possible with optical sources.

While in single mode step index fibers, coupling is not easy due to smaller diameter. Since it has smaller numerical aperture, therefore coupling is difficult with optical sources.

6.Tolerance Requirements
Lower tolerance requirements on Optical Fiber connectors in multimode step index fibers.

Tolerance requirements on optical fiber connectors are higher in case of single mode step index fibers.

FREQUENCY SPECTRUM OF AMPLITUDE MODULATION (WAVEFORMS AND EQUATIONS DERIVATION)

AMPLITUDE MODULATION (TIME DOMAIN EQUATIONS AND WAVEFORMS)

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

PULSE MODULATION TECHNIQUES (PAM, PWM, PPM, PCM)

OPTICAL FIBER: STRUCTURE AND WORKING PRINCIPLE

PULSE AMPLITUDE MODULATION (PAM)

COMPARISON OF PAM, PWM, PPM MODULATION TECHNIQUES

PULSE WIDTH MODULATION (PWM)

CONTINUOUS TIME AND DISCRETE TIME SIGNALS (C.T. AND D.T. SIGNALS)

NEED AND BENEFITS OF MODULATION

PULSE POSITION MODULATION (PPM)

OPTICAL FIBERS IN COMMUNICATION: COVERS ALL IMPORTANT POINTS

OPTICAL FIBER SOURCES (DESIRABLE PROPERTIES)

SAMPLING THEOREM AND RECONSTRUCTION (SAMPLING AND QUANTIZATION)

SUPERPOSITION THEOREM (BASICS, SOLVED PROBLEMS, APPLICATIONS AND LIMITATIONS)

Digital Modulation Techniques (ASK, FSK, PSK, BPSK)/ Amplitude, Frequency and Phase Shift Keying

Conventional AM Vs DSB-SC Vs SSB-SC Vs VSB (Comparison of AM Systems)

What are Microwaves and their Applications (Uses) in various fields

Basic Structure of Bipolar Junction Transistor (BJT) - BJT Transistor - Working and Properties

Polar Plots of Transfer Functions in Control Systems (How to Draw Nyquist Plot Examples)

Generation of Binary Phase Shift Keying (BPSK Generation) - Block Diagram of Binary Phase Shift Keying (BPSK)

Low Level and High Level Modulation Block Diagram (AM Transmitter Block Diagram)

Block Diagram of CRO (Cathode Ray Oscilloscope), Components of CRO and CRT with Structure and Working

Slope Overload Distortion and Granular (Idle Noise), Quantization Noise in Delta Modulation

Frequency Translation/Frequency Mixing/Frequency Conversion/Heterodyning (Basic Concepts and Need)

Quadrature Phase Shift Keying Modulation (QPSK) Basics, Waveform and Benefits

Pulse Code Modulation (PCM) Vs Differential Pulse Code Modulation (DPCM)

## 20 Sept 2017

### ADVANTAGES OF OPTICAL FIBER COMMUNICATION

Optical fibers have many good qualities that make it highly useful in different fields of our life. Here we will discuss various advantages (benefits) of Optical Fiber Communication

# Advantages of Optical Fiber Communication

1.Low transmission losses
2.Huge potential bandwidth
3.Small size, low weight and high flexibility.
4.Electrical isolation
5.Security of signal
6.No cross-talk and immunity to interference
7.Potential low cost
8.Reliable system
9.Not attractive for theft

# Advantages of Optical Fiber Communication Video [HD]

## 1.Optical Fibers offer Low Transmission Losses

*Total Internal Reflection (TIR) phenomenon takes place in optical fibers, which offer very low losses.
*Large spacing between repeaters is possible due to low losses
*Optical fibres can be used for long distance communication
*Transmission Losses are very low (0.2 decible/kilometre)
*Negligible transmission Losses in optical fibers are due to the following reasons-
#Material absorption
#Linear and nonlinear scattering
#Fibre bend losses

## 2.Optical Fibers Provide Huge Potential Bandwidth

*Light rays are used as the carrier waves. The light rays have very high frequency.
*The optical fibers provide very large bandwidth due to this high frequency carrier, since as the carrier frequency increases, the bandwidth increases.
*Bandwidth of optical fibers is around 10^14 Hertz.

#OPTICAL FIBER (STRUCTURE AND WORKING PRINCIPLE)

## 3.Optical Fibers are of Small Size, Low Weight and have High Flexibility

*Diameter of Optical Fibers is very small (slightly more than that of human hair)
*Optical fibers occupy less space
*These are very light weight
*Highly flexible
*Easy to transport and Store
*Optical fibers can be very useful at highly populated places to reduce congestion as these occupy less space

## 4.Electrical Isolation is provided by Optical Fibers

*Optical fibers are made of glass (silica) or plastic, these are nothing but the insulators.
*So the light rays travel inside the insulating material
*Therefore there is no chance of electrical shock, short circuit or sparking hazards etc.

## 5.Signal Security is also an advantage of using Optical Fibers

*Light rays propagate inside the core of the optical fiber
*Hacking of the signal is not possible
*If someone tries to steal the signals, then it can be easily detected.
*This feature of optical fibers is useful especially for military, banking and sending secret messages.

## 6.Optical Fibers help in No Crosstalk and are Immune to Interference

*In optical fibers, there is no interference in electrically noisy environment.
*There is no effect of EMI or RFI.
*Fibers can be cabled together without any cross-talk

## 7.Optical Fibers have Potentially Low Cost

*Optical fibers are made of glass (silica/sand) or plastic, available in plenty, so the cost of optical fibers is very low.
*Repeaters and other electronics is required in less amount
*Low cost of transportation, handling, storage and installation etc.
*LASER and photodiode, fiber connectors and couplers are expensive (Disadvantage)

## 8.Optical Fiber Communication System is very reliable

*Repeaters, amplifiers and other electronics is required in less amount, which makes it more reliable.
*Optical fibers can easily serve for 20-30 years
*High reliability reduces the maintenance and maintenance cost.

#OPTICAL FIBER COMMUNICATION BASICS [VIDEOS]

# Why Digital Communication?

We know, that the electronic communication can either be analog or digital.  Today’s world is going digital, so it is really important to understand, the advantages of digital communication, that are responsible for the digitalization everywhere.
So here in this post, we will see, why digital communication is preferred over analog communication? But there are also some disadvantages associated with the digital communication. These disadvantages will also be discussed here. So first let's start with the advantages of digital communication.

1. Digital communication systems are simpler and cheaper in implementation as compared to analog communication systems. It has become possible due to advancements in Integrated Circuits (IC) technology. These ICs are very small in size, reliable and cost-effective. Such ICs are used in digital communication,

2. In digital communication, it is possible to use multiplexing to merge speech, video and other forms of data for transmission over a common channel. The multiplexing is of various types like Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM) or Code Division Multiplexing (CDM).
I don’t want to deviate from the current topic, so I will discuss the multiplexing in separate post.

3. High level of privacy can be obtained in digital communication using data encryption technique. This privacy provides the facility to allow the transmitted signals, to be received only by the permitted receivers. This feature is of great importance in military applications.

4. In digital communication channel encoding is used. Because of this encoding, there is less accumulation of noise from repeater to repeater, in case of long-distance communication. Apart from this, the digital signals tend to be less affected by noise as compared to analog signals.

5.  It is possible to perform lots of operations on digital signals, like Digital Signal Processing (DSP), data compression, image processing etc.

6. It is easy to detect and correct errors in digital communication. This easy detection and correction of errors is possible due to the use of channel coding in digital communication.

So these were the advantages of using digital communication. These benefits encourage the use of digital communication in place of analog communication.
Now we will discuss some disadvantages that are associated with the digital communication.

1. More transmission bandwidth is required in digital communication as compared to analog communication. This is due to the increase in the data rate when analog signal is converted into digital signal.

2. In digital communication, in case of synchronous modulation, synchronization is required.

3. Due to various stages used in conversion, high power consumption is another drawback of digital communication.

4. Sampling error is introduced in the sampling of signal.
5. Circuits that are used in digital communication are comparatively more complex and sophisticated.

# What is Amplitude Modulation (AM)

Definition:-
Amplitude Modulation may be defined as a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value (amplitude) of the modulating (message or baseband) signal.
Note: [In case of Frequency modulation (FM), the frequency of the carrier wave varies, according to the instantaneous value of the modulating signal, while in Phase Modulation (PM), the phase of the carrier wave varies, according to the instantaneous value of the modulating signal.]

# Amplitude Modulation (AM modulation) Video [HD]

## What Will You Learn Here about Amplitude Modulation?

After reading this post, you will understand:-
#What is Amplitude Modulation (AM)
#Time Domain analysis of the Amplitude Modulation
#Equations of Amplitude Modulation (Time Domain)
#Waveforms of Modulating signal, Carrier signal and Amplitude Modulated wave and
#Properties of the amplitude modulation

# Equations of Amplitude Modulation (Time Domain)

As per the definition of the amplitude modulation we can express it mathematically as-

# What is Amplitude Modulation (AM)

## Definition:-

Amplitude Modulation, is a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value (amplitude) of the modulating (message or baseband) signal.

Note:-
In case of Frequency Modulation (FM) or Phase Modulation (PM), the frequency or phase respectively, of the carrier wave varies, according to the instantaneous value of the modulating (message) signal.

# FREQUENCY SPECTRUM OF AMPLITUDE MODULATION VIDEO [HD]

In the previous post, I discussed; what is amplitude modulation and its various properties. We talked about only the time domain analysis of the amplitude modulation. We saw here, how the waveform changes with time but here, we will discuss the frequency domain analysis of the amplitude modulation. Here you will see, how the spectrum of modulating signal, carrier signal and modulated wave looks like. I will also derive here the equation of AM wave in frequency domain. So let's start...