A. Lecture- Introduction optical fiber communication.

8/13/2019 A. Lecture- Introduction optical fiber communication.

1/57

Optical CommunicationSystems

NITIN KUMARAsst Professor

Electronics And CommunicationEngineering Deptt

Sunderdeep Engineering college


2/57

OVERVIEW

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 speednetworks.

Optical Fiber Solutions for todays Systems &Networks.


3/57

An Information Model

Definition:

Delivering information to anauthorized user when it isneeded, wherever it is neededi.e,regardless of the physical

location of the user or of theinformation, and whatever formit is neededin a secure way.


4/57

Information SystemsEvolution

Compared to legacy systems todays Systemsare:

- Data oriented, large, and complex

- On-line, interactive with strong emphasis onuser interface e.g. Graphical User Interface

- Global, distributed and extensive in theirreach

- More volatile and subjective to constant

change Todays systems often require reuse of

components of existing systems and buildingnew systems to deal with changes


5/57

Needs For Todays Optical Systems

Increase capacity of transmission(bit/sec).

Minimize insertion loss (dB).

Minimize polarization dependent loss(PDL).

Minimize temperature dependence of

the optical performance (a thermalsolutions).

Minimize component packaging size(integrability).

Modularity of components is anadvantage (versatility)


6/57

Trends

Internet:A Deriving force

SOME ACTUAL FACTS 12 Million emailmessages in next minute

0.5 Million voicemail messages in next minute 3.7 Millionpeople log on the net today

Next 100 days, Internet traffic doubles

100 Millionadditional internet users every yearData based on the survey at Bell Laboratories, USA in Nov., 2000.DEMAND FOR MORE BANDWIDTH

ONLY SOLUTION IS

OPTICAL COMMUNICATION


7/57

The Race for Bandwidth

1995 2001World WideWeb Users

6 Million 300+Million

World WideWeb Servers 100K 17+Million

MonthlyInternet

Traffic

31 Terabytes 350,000Terabytes

InternetBackbone

Demand

DoublesEvery 6

Months


8/57

Exploding Demands forBandwidth


9/57

Optical Fiber Bandwidth as a function of time40 X OC92 denotes 40 wavelength channels

OC-48= 2.5Gb/s, OC-192=10Gb/s, OC-768=40Gb/s


10/57

#WDM-ch

annels

4

16

64

256

0.01 0.1 1 10 100

Channel bitrate (Gb/s)

1

Trunk transmission capacity

97

98

9899

00

02?

86

96

89

83

80


11/57

Do We Need Terabits ?

Information Systems

Computing Shift

The Internet Ligthwave Capacity

Trends

Global Networking


12/57


13/57

Facts Regarding OpticalTransmission

BIT RATE INCREASING

TRANSMISSION DISTANCE INCREASING


14/57

Capacity Growth of Optical FiberEach Year

Year Capacity (Gb/s)

1980 0.1

1985 1 1990 3

1995 5

2000 100 (40 practically shown) 2005 1,000 (If

limitations due to Dispersion &Nonlinearities are overcome)


15/57

The optical world is approaching

towards

1. 50 THzTransmission Window

1000Channel WDM

100 Gb/sTDM

1000 kmRepeater less transmission

If Nonlinearities can becontrolled, transmission windowwill be 300THz


16/57

Optical Fiber Applications


17/57

Fiber to the Home


18/57

OFC Backbone Capacity


19/57

Bandwidth-What is it ?

Bandwidth is the a measure of informationcarrying capacity of a medium.

To the digital word, it is translated into a

maximum bit rate at which signals can be sentwithout significant signal degradation

Fiber bandwidth is typically quoted in frequencyand normalized to fiber length (MHz-Km)

-As length increases bandwidth decreases

A fiber bandwidth is determined by its pulsespreading properties


20/57

Bandwidth-What is it ?

The difference between the highestand lowest frequencies of a bandthatcan be passed by a transmission

medium without undue distortion.

A term used to indicate the amount oftransmission or processing capacity

possessed by a system or specificlocation in a system(Usually a networksystem)


21/57

Copper Versus Fiber: Repeaters


22/57


23/57

Eliminate the dangers found in areas of

high lightning-strike


24/57

Fiber links offer over 1,000 times asmuch bandwidth and distances over

100 timesDistance Bandwid

thVoice

Channels

Copper 2.5 km 1.5 Mb/s 24

Fiber 200 KM 2.5+Gb/s

32,000 +


25/57

Electromagnetic Spectrum


26/57

Introduction to OpticalCOmmunication

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 use Laser& Optical Fiber technologies.

Optical frequency is typically 1014Hz, which can

support wideband modulation. Compared tomicrowave frequencies 109Hz, the optical careercan offer 105 times more bandwidth.


27/57

Basics of Fiber Optic Communication

Fiber Optics is a revolutionary developmentthat has changed the face oftelecommunications around the world

Transmission of data as a light pulsesthrough optical fiber (first convertingelectronic binary signals to light and then

finally converting back to electronicsignals)

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


28/57

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 operationVery 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


29/57

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 for total internal reflection

Light entering with acceptance angle propagates throughfiber Strikes core cladding interface > critical angle and gets

reflected completely.

Zig-zags down length of 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 )


30/57


Major Advantages of FOC

Large Bandwidth (Extremely high information carryingcapacity)

Carrier frequencyLight1014Hz

Makes possible widespread long distance communication ofhigh bandwidth signals

Color video High speed network

High degree of Multiplexing, without much interference amongthem.

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)


31/57


Major Advantages of FOC (Contd..)

Compact and light weight Single fiber can easily replace 1000 pair copper cable of

10 cm dia.

Security (impossible to tap)

Safety (insulator & no sparksideal for hazardous

environment) Can be used in

Oil exploration

Oil refineries

Mines

Explosives

Petrochemical

Other hazardous chemical


32/57


Some practical disadvantages of FOC

Fiber is expensiveConnectors 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


33/57

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 compoundsemiconductor

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


34/57

Advances in Optical Communication (Contd..)

Present Standards Supported:Various multiplexing techniques for enhanced capacityutilization, use of optical amplifiers & Soliton basedtransmission systems developed.

Speed & Repeater spacing due to fiber optic systems, newer

standards such as:FDDI (Fiber Distributed Data Interface)

DQDB (Dual Queue Distributed Bus)

SONET (Synchronous Optical Network)

SDH (Synchronous Digital Hierarchy)


35/57

Advances in Optical Communication (Contd..)More Advanced Systems:

Era of high capacity Trans Atlantic Telecommunication (TAT)

began as under:TAT - 2 in 1959

TAT 6 in 1976

TAT 7 in 1983 (offered a capacity of about 4000 analogcircuits)

Optical fiber based TAT 8 in 1989 (offered 40,000 circuits,

64,000 Km long, 280 Mbps, 40 Km repeater distance )TAT - 12/13 with many new features is now operational

Some other fiber systems include HAW 4 (Hawaiian Cable4), TPC 3(Trans Pacific Cable 3)


36/57

Advances in Optical Communication (Contd..)Further achievements include

Fiber losses 0.16 dB/Km (at 1550 nm)

Laser with threshold currents of few milli-amperes andlife time of over a million hours

Repeater spans of more than 200 Kms.

Transmission rates in excess of 2 Gbps

Advent of EDOFA (Erbium-Doped optical fiber amplifier),

using dispersion compensating Soliton transmissiontechniques or the use of dispersion compensating fibers(DCF) and the improvements made in the attenuation &dispersion characteristics of the modern optical fiber haveled to the demonstration of data transmission inexperiments with repeaterless spans of over 10,000 Km

and bit rates in excess of 10 GbpsMore complex coherent optical communication,wavelength routed, dense wavelength divisionmultiplexing (DWDM) links are available.


37/57

Advances in Optical Communication (Contd..)Coherent communication systems make use of:

Sources & detectors made of quantum well

structures with high directional properties.Single mode single polarization optical fiber havingvery low loss and very low dispersion.

Has superior SNR capabilities, long repeater spans& high bit rates.

WDM (Wavelength Division Multiplexing)

Provides an easy way to increase the utilization ofthe high channel channel capacity of the optical fiber.

Integrated Optics

Deals with the miniaturization & integration on asingle substrate optical components such as

- electro optic modulator

- polarization controller

- splitters / combiners

- directional couplers

- lenses


38/57


-Optical MEMs make use of silicon micro machining torealize micro-opto-mechanical elements

-Soliton Propagation in Optical Fibers

-Initially launched pulse may propagate with ultra-lowdispersion over thousands of Kilometers

-Active devices within fibers EDFA (Erbium DopedFiber Amplifiers) are now available.

-Photonic switching architectures (which useintegrated optic switches) & optical MEMs providesdata rate transparent switching services to opticalfiber based trunks


39/57


S i g n a l s V o i c e , D a t a , V i d e o , I n t e g r a t e d S e r v i c e s

S y s t e m s P o i n t - t o - P o i n t , M u lt i p o i n t , S h o r t - h a u l ,

L o n g - H a u l ( U n d e r s e a )

S t a n d a r d s S O N E T / S D H , F D D I , I S D N , B I S D N , A T MD e p l o y m e n t L A N , M A N , W A N , C A T V , H F C , F T T C ,

F T T H

P h o t o n i c

T e c h n o l o g y

P h o t o n ic s w i t c h i n g , W D M / T D M / O F D M ,

A l l o p t i c a l / p h o t o n i c n e t w o r k s , S o l i t o n

S y s t e m s , O p t i c a l a m p l i f i c a t i o n

Features of Present OpticalCommunication


40/57

Advances in Optical Communication (Contd..)System Design Issues

Source Receiver Fiber

LED Laser

Diode

Detector Amplifier

Quantum Quantum

NoiseNoise

Quantum Noise Optical:

Spontaneousemission noise

Mode partition

noise

Bandwidth Mode

Limit Partition

noise

Bandwidth

Limit

Shot noise Electronic:

Shot

& thermal

noise

Bandwidth BandwidthLimit Limit

Dispersion limit

Non-linear effects


41/57


42/57

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 1.7Wavelength (

m)


43/57

Fiber Structure

A Core Carries most of the light, surrounded by

A Cladding, Which bends the light and confinesitto the core, covered by

A primary buffer coating which providesmechanical protection, covered by

A secondary buffer coating, which protectsprimary coating and the underlying fiber.


44/57

Fiber Structure Cont


45/57

Types Of Optical Fibre

Single-mode step-index fibre

Multimode step-index fibre

Multimode graded-index fibre

n1core

n2cladding

noair

n2cladding

n1core

Variable

n

noair

Light

ray

Index porfile


46/57

Multimode Step Index Fiber

Core diameter range from 50-1000m

Light propagate in many different raypaths, or modes, hence the name

multimode

Index of refraction is same all across thecore of the fiber

Bandwidth range 20-30 MHz


47/57

Multimode Graded Index Fiber

The index of refraction across the coreis gradually changed from a maximumat the center to a minimum near the

edges, hence the name Graded Index Bandwidth ranges from 100MHz-Km to

1GHz-Km

l S d


48/57

Pulse Spreading

time

Pulse from zero-order mode

Pulse from highest-order mode

Pulses from other modes

Resulting pulse

T

T

T

T

T


49/57

Calculation of Pulse Spread

C

C

x

y/2 y/2

Cyx cos


50/57


51/57

Modes of Vibration of a String

Lowest order mode

Second order mode

Third order mode

)sin( 01 tA

)2sin( 02 tA

)3sin( 03 tA


52/57

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

T i l C d Cl ddi


53/57

Typical Core and CladdingDiameters (m)

A t C & N i l


54/57

Acceptance Cone & NumericalAperture

n2cladding

n2cladding

n1core

Acceptance

Cone

Acceptance angle, qc, is the maximum angle in which

external light rays may strike the air/fibre interface

and still propagate down the fibre with


55/57

Multiple OFC


56/57

Standard Optical Core Size

The standard telecommunications core sizes in

use today are:

8.3 m (single-mode),

50-62.5 m (multimode)


57/57

Thanks

A. Lecture- Introduction optical fiber communication.

Documents

Transcript of A. Lecture- Introduction optical fiber communication.