# 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)

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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)

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