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Transcript of AOC Lecture 1 by Dr
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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.
Historical Developments - 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
Historical Developments - contd.
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