AOC Lecture 1 by Dr

7/24/2019 AOC Lecture 1 by Dr

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ICT 6612: Advanced Opti cal Communications

Syllabus (salient features):

Introduction to optical communication

Optical fiber waveguides

Optical sources & detectors: LED, Laser, PIN, APD Fiber connections: MUX, DEMUX, OADM

Optical amplifiers: SOA, EDFA etc.

Optical modulation and detection scheme

Fiber nonlinearities: SPM, XPM, FWM, SBS, SRS

Transmission link analysis

Optical multiplexing schemes: WDM, OFDM, OTDM etc.

Reference books:

Fiber Optic Communication Technology

-- Djafar K. Mynbaev & Lowell L. Scheiner

Optical Fiber Communications: principles and practice ( 2nd or3rd edition)

---John M. Senior

Optical Fiber Communications ( 3rd or 4th edition)--- Gerd Keiser

Fiber-Optic Communication System (3rd edition)-- Govind P. Agrawal

Electrical & Optical communication


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Advantages of optical technology Demand for Bandwidth

BandwidthDemand

1990 2000 2010

Raw text = 0.0017 Mb Word document = 0.023 Mb Word document with picture = 0.12 Mb Radio-quality sound = 0.43 Mb Low-grade desktop video = 2.6 Mb CD-quality sound = 17 Mb Good compressed (MPEG1) video = 38 Mb

Typical data bandwidth requirement

20,000 x

Communications Technologies

Year Service Bandwidth distance product

1900 Open wire telegraph 500 Hz-km

1940 Coaxial cable 60 kHz-km

1950 Microwave 400 kHz-km

1976 Optical fibre 700 MHz-km

1993 Erbium doped fibre amplifier 1 GHz-km

1998 EDFA + DWDM > 20 GHz-km

2001- EDFA + DWDM > 80 GHz-km

2001- OTDM > 100 GHz-km

Increase in Bitrate-Distance product

Agrawal-Fiber Optic Communications


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Historical Developments

800 BC Use of fire signal by the Greeks

400 BC Fire relay technique to increase transmission distance

150 BC Encoded message

1880 Invention of the photophone by Alexander Graham Bell

Historical Developments - contd.

1930 Experiments with silica fibres, by Lamb (Germany)

1950-55 The birth of clad optical fibre, Kapany et al (USA)

1962 The semiconductor laser, by Natan, Holynal et al (USA)

1960 Line of sight optical transmission using laser:- Beam diameter: 5 m

- Temperature change will effect the laser beam

Therefore, not a viable option

1966- A paper by C K Kao and Hockham (UL) was a break

through

- Loss < 20 dB/km- Glass fibre rather than crystal (because of high viscosity)

- Strength: 14000 kg /m2.

Contd.


1970 Low attenuation fibre, by Apron and Keck (USA) from 1000

dB/km - to - 20 dB/km- Dopent added to the silica to in/decrease fibre refractive index.

Late 1976 Japan, Graded index multi-mode fibre

- Bandwidth: 20 GHz, but only 2 GHz/km

Start of fibre deployment.

1976 800 nm Graded multimode fibre @ 2 Gbps/km.

1980s

- 1300 nm Single mode fibre @ 100 Gbps/km

- 1500 nm Single mode fibre @ 1000 Gbps/km

- Erbium Doped Fibre Amplifier


1990s

- Soliton transmission (exp.): 10 Gbps over 106 km with no error

- Optical amplifiers

- Wavelength division multiplexing,

- Optical time division multiplexing (experimental) OTDM

2000 and beyond

- Optical Networking- Dense WDM, @ 40 Gbps/channel, 10 channels

- Hybrid DWDM/OTDM ~ 50 THz transmission window

> 1000 Channels WDM

> 100 Gbps OTDM

Polarisation multiplexing

- Intelligent networks


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Lightwave transmission band Applications

Optical Communication Systems High Speed Long Haul Networks

(Challenges are transmission type)

Metropolitan Area Network (MAN) ?

Access Network (AN)?Challenges are:

- Protocol

- Multi-service capability

- Cost

Electronics and Computers

Broad Optoelectronic

Medical Application

Instrumentation

Lightwave Application Areas

Optical interconnects

Chip to Chip (Unlikely in near future)Board to Board (>1foot eg. CPU-Memory)Subsystem-Subsystem (Optics used Low Speed) Telecommunications

Long Haul (Small Market-High Performance)LANs (Large Market Lower Performance)

High-Speed Analog (CATV-Remote Satellite)

Optical fiber


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Optical fiber Fiber With Cladding

Developed in 1954 byvan Heel, Hopkins &Kapany

Cladding is a glass orplastic cover around thecore

Protects the total-reflection surfacecontamination

Reduces cross-talkfrom fibers in bundles

General and Optical Communication

systems


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System Block Diagram Evolution of Light wave systems

Exampleof a laser diode.

(Ref.: Infineon)

1. Generation: The development of low-lossfibers and semiconductor lasers (GaAs) in the1970s.

A Gallium Aresenide (GaAs) laser operates at awavelength of 0.8m. The optical

communication systems allowed a bit rate of45Mbit/sand repeater spacing of 10km

Source

Source

codingModula tion Multiplexing Modulat ion

External Internal

Analogue

Digital

Frequency

Time

Pulse shaping

Channel coding

Encryption

etc.

Receiver

1st-stage

amplifier

2nd-stage

amplifier

Pre-detection

filtering

Sampler

&

detector

Demultiplexer

Equalizer Demodulator

Output signal

Decoder

Decryption


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Optical Fiber System

State of the Art optical communication system: Dense Wavelength DivisionMultiplex (DWDM) in combination of optical amplifiers. The capacity of opticalcommunication systems doubles every 6 months. Bit rates of 10Tbit/s were

realized by 2001.

Ref.: S. Kartalopoulos, WDWM Networks, Devices and Technology

Evolution of Lightwave systems

Transmission windowsOptical Fiber Attenuation and Fiber Ampl ifier Gain


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Global Undersea Fiber systems Global Undersea Fiber systems

Challenges Ahead

Modulation and detection and associated high speed electronics

Multiplexer and demultiplexer

Fibre impairments:

. Loss

. Chromatic dispersion

. Polarization mode dispersion

. Optical non-linearity

. etc.

Optical amplifier

. Low noise

. High power

. Wide bandwidth

. Longer wavelength band S

Challenges Ahead - contd.

Dedicated active and passive components

Optical switches

All optical regenerators

Network protection

Instrumentation to monitor QoS


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Propagation of light pulses in the

presence of chromatic dispersion

Chromatic dispersion distortion of pulse shape

Chromatic Dispersion

60 Km SMF-28

4 Km SMF-28

10 Gbps

40 Gbps

t

t

It causes pulse distortio n, pulse "sm earing"effects

Higher bit-rates and shorter pulses are less

robust to Chromatic Dispersion

Limits "how fast and how far data can travel

Dispersion Compensating Fibre

By joining fibres with CD of opposite signs (polar ity) andsu itable lengths an average

dispersion close to zero can beobtained

The compensating fiber can beseveral kilometers and the reelcan be inserted at any poin t inthe l ink, at the receiver or at the

transmitter


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Theoretical chromatic dispersion for

fused silica fibre Polarization Mode Dispersion (PMD)

The optical pulse tends to broaden as it travels down the fiber.

This is a much weakerphenomenon than chromatic dispersion andit is of some relevance at bit rates of 10Gb/s or more

nx

nyEx

Ey

Input pulse Spreaded output pulse

Bit rate versus distance limitation imposed bydifferent types of dispersion

Classification based on mode of pro pagation


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Classification based on RI in the core

Step index

Graded index

Step-Index Fiber

Cladding typically pure silica

Core doped with germanium to increase

index

Index difference referred to as delta in unitsof percent (typically 0.3-1.0%)

Tradeoff between coupling and bending

losses

Index discontinuity at core-clad boundary

Basic Step index Fiber Structure Graded Index Fiber

Fiber Optic Communication Systems-Agarwal

Fiber Optic Communications-Palais


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Optical Transport Network

Global Network

Wide AreaNetwork

Metropolitan/RegionalArea Opti cal Netwo rk

Corporate/Enterprise Clients

Cable modem

Networks

Client/AccessNetworks

FTTH

Mobile

SDH/SONET

ATM

PSTN/IP

ISPGigabitEthernet

Cable

FTTB

ATM

< 10000 km< 10 Tbit/s

< 100 km< 1 Tbit/s

< 20 km

100M - 10 Gbit/s

Decibels

Decibels are a logarithmic scale of power

Abbreviated dB

A loss of 10 decibels means only 10% of the

light gets through

A loss of 20 dB means 1% of the light gets

through

Sunglasses stop 99% of light, so they cause a loss of

20 dB

For communications, loss must be no more than

10 or 20 decibels per kilometer

AOC Lecture 1 by Dr

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