lec 1 advanced comm ( introduction)

7/31/2019 Lec 1 Advanced Comm ( iNTRODUCTION)

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Today, almost all of the wired and wireless

communication is digital.Digital Communication

offers following advantages over analog

High SNR

Easy Signal processing

Error detection and correction

Multiplexing

Cheaper circuitry

Easy detection of signal; we have to detect the

presence(1) or absence of signal(0).


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Modern electronic communication systems can be broadly

classified into following types:1. Optical Communication

2. Mobile Communication

3. Satellite Communication


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Optical Communication

AN OVERVIEW


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Electrical Communication

Optical Communication

Structure of Optical Fiber and Optical Fiber Cable


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The spread of the use of Optical Communication through-out the world


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Information Systems Evolution & What is it ?

Why there is Demand of Large bandwidth ?

Why Optical Fiber Technology ?

Optical Transmission fundamentals.

How to Explode the optical fiber bandwidth ?

Data rate requirements for high speed networks.

Optical Fiber Solutions for todays Systems &Networks.


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An Information Model

Definition:

Delivering information to an authorized

user when it is needed, wherever it is

needed i.e, regardless of the physical

location of the user or of the

information, and whatever form it isneeded in a secure way.


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Needs For Todays Optical Systems

Increase capacity of transmission(bit/sec).

Minimize insertion loss (dB).

Minimize polarization dependent loss(PDL).

Minimize temperature dependence ofthe optical performance (a thermalsolutions).

Minimize component packaging size(integrability).

Modularity of components is anadvanta e versatilit


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Trends

Internet: A Deriving force

SOME ACTUAL FACTS

12 Million email messages in next minute

0.5 Million voice mail messages in next minute

3.7 Million people log on the net today

Next 100 days, Internet traffic doubles

100 Million additional internet users every yearData based on the survey at Bell Laboratories, USA in Nov., 2000.

DEMAND FOR MORE BANDWIDTH

ONLY SOLUTION IS

OPTICAL COMMUNICATION


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The Race for Bandwidth

1995 2001World Wide

Web Users

6 Million 300+

Million

World WideWeb Servers

100K 17+Million

Monthly

Internet Traffic

31 Terabytes 350,000

Terabytes

Internet

Backbone

Demand

Doubles

Every 6

Months


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Exploding Demands for

Bandwidth


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Facts Regarding Optical

Transmission

BIT RATE INCREASING

TRANSMISSION DISTANCE INCREASING


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Capacity Growth of Optical Fiber

Each YearYear Capacity (Gb/s) 1980 0.1

1985 1

1990 3

1995 5

2000 100 (40 practically shown)

2005 1,000 (If limitationsdue to Dispersion & Nonlinearities areovercome)


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The optical world is approaching

towards 1. 50 THzTransmission Window

1000Channel WDM

100 Gb/sTDM

1000 kmRepeater less transmission

If Nonlinearities can be controlled,transmission window will be 300THz


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Optical Fiber Applications


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OFC Backbone Capacity


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Bandwidth-What is it ?

Bandwidth is the a measure of information carryingcapacity of a medium.

To the digital word, it is translated into a maximum

bit rate at which signals can be sent withoutsignificant signal degradation

Fiber bandwidth is typically quoted in frequency andnormalized to fiber length (MHz-Km)

- As length increases bandwidth decreases

A fiber bandwidth is determined by its pulsespreading properties


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Bandwidth-What is it ?

The difference between the highest and

lowest frequencies of a band that can be

passed by a transmission mediumwithout undue distortion.

A term used to indicate the amount of

transmission or processing capacity

possessed by a system or specific

location in a system (Usually a network

system)


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Copper Versus Fiber: Repeaters


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Eliminate the dangers found in areas of

high lightning-strike


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Fiber links offer over 1,000 times as

much bandwidth and distances over

100 timesDistance Bandwidth Voice

Channels

Copper 2.5 km 1.5 Mb/s 24

Fiber 200 KM 2.5+ Gb/s 32,000 +


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Introduction

The first practical scheme of opticalcommunication, was invented by AlexanderGrahm Bell, in 1880, the Photophone.

Photophone: Device in which speech can be

transmitted on a beam of light, using mirrors &selenium detectors.

Present optical communication systems useLaser & Optical Fiber technologies.

Optical frequency is typically 1014 Hz, whichcan support wideband modulation. Comparedto microwave frequencies 109 Hz, the opticalcareer can offer 105 times more bandwidth.


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Basics of Fiber Optic Communication Fiber Optics is a revolutionary development that has changed the

face of telecommunications around the world

Transmission of data as a light pulses through optical fiber (first

converting electronic binary signals to light and then finally

converting back to electronic signals)

Elements of Fiber Optics

Transmission

Light Source (such as Infrared LED converts pulses and sends

into optical fiber)

850 nm, 1300 nm Low cost, easy to use

Used for multi mode fiber

Special edge emitting LEDs for single mode fiber


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Basics of Fiber Optic Communication (Contd..) Laser Source having properties

Coherence

Monochromaticity Directionality

High Specific Intensity

850 nm, 1300 nm, 1550 nm

Very high power output

Very high speed operation

Very expensive

Need specialized power supply & circuitry

Reception

Photo detector converts back to electrical pulses

PIN DIODES

850, 1300, 1550 nm

Low cost

APDs (Avalanche Photodiodes)

850, 1300, 1500 nm

High sensitivity, can operate at very low power levels

expensive


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Basics of Fiber Optic Communication (Contd..)

Propagation in Fiber

Light propagates by mans of total internal reflection.

Optical Fiber consists of two concentric layers

Coreinner layer

Claddingouter layer

Refractive index of core is greater than cladding, necessary fortotal internal reflection

Light entering with acceptance angle propagates through fiber

Strikes core cladding interface > critical angle and getsreflected completely.

Zig-zags down lengthof core through repeated reflections. Fairly lossless propagation through bends also.

Optical fiber

Multimode (Graded Index 50/125 & 62.5/125 )

Single mode (8.7 /125 )


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Major Advantages of FOC

Large Bandwidth (Extremely high information carrying capacity)

Carrier frequencyLight1014 Hz

Makes possible widespread long distance communication of

high bandwidth signals

Color video

High speed network High degree of Multiplexing, without much interference

among them.

Low Loss (Long repeaterless link length/repeater spacing)

Loss as low as 0.1 dB/Km

Repeater spacing of over 100 Km possible over land & under

sea.

EMI immunity (Even in noisy or harsh environments-Lightning,

factory floor, high voltage lines, broadcast towers)


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Some practical disadvantages of FOC

Fiber is expensive Connectors very expensive (due to degree of

precision involved)

Connector installation time consuming &

highly skilled operation Joining (splicing) of fibers requires expensive

equipment & skilled operators

Connections & joints are relatively lossy

Difficult to tap in & out (for bus architectures)need expensive couplers

Relatively careful handling required


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Advances in Optical Communication First Generation Support:

Operating at: 850 nm

Bit Rates: 50 -100 Mbps

Repeater Spans: 10 Kms

Sources & Detectors made of InGaAsP compound semiconductor

Second Generation Support:

Operating at: 1300 nm Bit Rates: 1-2 Gbps

Repeater Spans: 40 -50 Kms

Sources & Detectors made of InGaAsP compound semiconductor

Third Generation Support:

Operating at: 1550 nm

Bit Rates: 2.4 Gbps

Repeater Spans: 100 Kms


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Optical Communication Systems

First Generation, ~1975, 0.8 mMM-fibre, GaAs-laser or LED

Second Generation, ~1980, 1.3 m, MM & SM-fibreInGaAsP FP-laser or LED

Third Generation, ~1985, 1.55 m, SM-fibreInGaAsP DFB-laser, ~ 1990 Optical amplifiers

Fourth Generation, 1996, 1.55 mWDM-systems

1.80.8 1.0 1.2 1.4 1.60.9 1.1 1.3 1.5 1.7

Wavelength (m)


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Information Transmission

Sequence


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Fiber Structure A Core Carries most of the light, surrounded by

A Cladding, Which bends the light and confines it to

the core, covered by

A primary buffer coating which provides mechanicalprotection, covered by

A secondary buffer coating, which protects primary

coating and the underlying fiber.


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Fiber Structure Cont


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Types Of Optical Fibre

Single-mode step-index fibre

Multimode step-index fibre

Multimode graded-index fibre

n1 core

n2 cladding

no air

n2 cladding

n1 core

Variable

n

no air

Light

ray

Index porfile


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Multimode Step Index Fiber Core diameter range from 50-1000m

Light propagate in many different ray paths, or

modes, hence the name multimode

Index of refraction is same all across the core ofthe fiber

Bandwidth range 20-30 MHz


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Multimode Graded Index Fiber

The index of refraction across the core is

gradually changed from a maximum at the

center to a minimum near the edges, hence the

name Graded Index

Bandwidth ranges from 100MHz-Km to

1GHz-Km


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Pulse Spreading

time

Pulse from zero-order mode

Pulse from highest-order mode

Pulses from other modes

Resulting pulse

T

T

T

T

T


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Single-Mode Graded Index Fiber

The Core diameter is 8 to 9m

All the multiple-mode or multimode

effects are eliminated However, pulse spreading remains

Bandwidth range 100GHz-Km


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Typical Core and Cladding

Diameters (m)

M lti l OFC


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Multiple OFC


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Standard Optical Core Size

The standard telecommunications core sizes in

use today are:

8.3 m (single-mode),

50-62.5 m

(multimode)

lec 1 advanced comm ( introduction)

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