Dr. Hanna A.
Kirolous
Professor
Electronics and Communications Engineering Department
Faculty of Engineering
Cairo University
Spring 2020
Optical Fiber Communications Introduction
Optical Fiber Communication System
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Optical Fiber Communications Introduction
Optical Fiber Communication System
Signal
Splice
Circuit source
(Digital)
fiber
Repeater
detector
source channel
coupler detector conditioner signal
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Optical Fiber Communications Introduction
Course Outline
• Optical versus radio frequency communications.
• Optical fibers.
• Ray representation in optical fibers.
• Modal analysis in step-index optical fibers.
• Signal attenuation and distortion.
• Optical properties of semiconductors Emitters: laser
diodes & light emitting diodes.
• Photo detectors: PIN & avalanche photo diode (APD).
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Optical Fiber Communications Introduction
Course Outcomes
• Clearly describe the concepts of optical communications in
comparison to traditional electrical systems.
• Derive and analyze the physics of light confinement in
multimode fibers using geometrical optics approximations.
• Derive, analyze and interpret the physical meaning of the
dispersion formulae in single and multimode fibers using
electromagnetic model.
• Identify, tabulate and analyze the sources of signal distortion
and attenuation in optical fibers.
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Optical Fiber Communications Introduction
Course Outcomes
• Comprehend the fundamentals of semiconductor optical
sources (Light-emitting and laser diodes) used in communication
systems and be capable of characterizing there parameters and
drive circuits.
• Comprehend the fundamentals of semiconductor optical
detectors (PIN and Avalanche photodiodes) used in
communication systems and be capable of characterizing there
parameters.
• Conduct research and prepare presentation on selected topics
related to optical communications.
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Optical Fiber Communications Introduction
References
Course Text Book:
John A. Buck, “Fundamentals of Optical Fibers”, 2nd Edition
John-Wiley & Sons, 2004
References:
J.C. Palais, “Fiber Optic Communications” Fifth Edition,
Prentice Hall, 2005
G. D. Agrawal, “Fiber Optic Communication Systems” Third
Edition, John-Wiley & Sons, 2002
Course Web Page:
Course Name: Optical Fibers (Elective 3)
Hosted by: http://moodle.eece.cu.edu.eg
Use Enrollment Key : OF-Elective-S20
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Optical Fiber Communications Introduction
Grading System
Midterm exam. 15 %
Assignments 15 %
Final exam 70 %
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Optical Fiber Communications Introduction
Evolution of Communication Systems
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Optical Fiber Communications Introduction
Evolution of Communication Systems
Distance
Year of
System Bit Rate between Limitations
Emergence
Repeaters
1830 Telegraphy 10 b/s 1000 m
Telephony
1880 Analog 1000 m
(Twin pairs)
Telephony 3 MHz BW
1940 10 Km Capacitance
(coaxial cables) (300 Channels)
4 GHz carrier • Carrier Frequency
1948 Microwaves 10 Km
(100 Mb/s) • Expensive
Started at: • Coherent light source
1974 Light waves 10 Km
50 – 100 Mb/s • Losses in optical fibers
Optical
1990 2.5 Gb/s 4500 Km
amplifiers
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Optical Fiber Communications Introduction
Evolution of Optical Fiber Systems
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Optical Fiber Communications Introduction
Evolution of Optical Fiber Systems
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Optical Fiber Communications Introduction
Evolution of Optical Fiber Systems
Bit-
Gener λ
Year Fiber Modulation Rate L (Km) Comments
ation (µm)
(Gb/s)
Multi- Direct- 0.05- Problems with inter-modal
1 1978 0.8 10
mode detection 0.1 dispersion & High losses
Single- Direct- @ 1.3 µm -> min.
2 1980 1.3 1.7 50
mode detection dispersion (loss < 1 dB/Km)
@ 1.55 µm -> min. loss (0.2
Single- Direct- dB/Km) + dispersion-
3 1990 1.55 2.4 100
mode detection shifted fibers + InGaAsP
lasers
Single-mode lasers
Exp. Single- Coherent
4 1.55 2.5 2000 Erbium-doped fiber
1980 mode detection amplifiers
Exp. Single- Fiber 4000- Fiber nonlinearity corrects
5 1.55 20
1990 mode Solitons 12000 for transmission dispersion
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Optical Fiber Communications Introduction
Commercial vs. Research in Optical Fiber Systems
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Optical Fiber Communications Introduction
Acceleration of Bit-Rate in Optical Fiber Systems
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Optical Fiber Communications Introduction
Acceleration of Bit-Rate in Optical Fiber Systems
WDM Per channel
Year Organization Effective speed Distance
channels speed
2009 Alcatel-Lucent 15.5 Tbit/s 155 100 Gbit/s 7000 km
2010 NTT 69.1 Tbit/s 432 171 Gbit/s 240 km
2011 NEC 101.7 Tbit/s 370 273 Gbit/s 165 km
2011 KIT 26 Tbit/s >300 50 km
5.6 Tbit/s circa
2016 BT & Huawei 28 200 Gbit/s
140 km ?
Nokia Bell
Labs, Deutsche Telekom 1 Tbit/s
2016 1 1 Tbit/s
T-Labs & Technical
University of Munich
65 Tbit/s
2016 Nokia-Alcatel-Lucent 6600 km
11.2 Tbit/s
2017 BT & Huawei 28 400 Gbit/s 250 km
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Optical Fiber Communications Introduction
Advantages of Optical Communications
Low transmission loss. More data over longer distances
less repeaters
Wide bandwidth. less cost & complexity
Small size and weight.
Immunity to interference (EMI & EMP).
Electrical insulation (No arcing, sparking, ground
loops, hazards).
Signal security (banking, computer networks,
military systems).
Abundant raw material.
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Optical Fiber Communications Introduction
Optical Fiber Cable Installation
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Optical Fiber Communications Introduction
Fiber Wavelength Windows
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Optical Fiber Communications Introduction
Nature of Light
Models for Studying Light Propagation
Quantum Physics Wave Optics Geometrical Optics
𝐸𝑝ℎ = ℎ 𝜈 𝐸
ഫ and 𝐻
ഫ (Using Rays)
All Phenomena All Phenomena Only reflection and
Including: radiation, except: radiation, refraction
emission, emission, absorption.
absorption,…. Etc.
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Optical Fiber Communications Introduction
Rays and Waves
𝛥 >> 𝜆
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Optical Fiber Communications Introduction
Reflection and Refraction
𝜙 ′1
Snell’s Law: 𝜙1 = 𝜙 ′1 and 𝑛1 sin𝜙1 = 𝑛2 sin𝜙2
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Optical Fiber Communications Introduction
Total Reflection
𝜙1 < 𝜙𝑐 𝜙1 = 𝜙𝑐
𝑛1 sin𝜙𝑐 = 𝑛2
𝑛2
𝜙𝑐 = sin−1
𝑛1
𝜙1 > 𝜙𝑐
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Optical Fiber Communications Introduction
Single Fiber Structure
𝑛1
𝑛2 < 𝑛1
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Optical Fiber Communications Introduction
Comparison of Fiber Structures
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Optical Fiber Communications Introduction
Skew Rays
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Optical Fiber Communications Introduction
Meridional Ray Representation
𝑛𝑜
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Optical Fiber Communications Introduction
Multimode vs. Single mode Fibers
Multi-mode Single mode
Signal power is distributed Smaller core diameter makes:
over a number of modes, • Optical coupling less
each traveling at slightly efficient
different group velocity , • Splicing is more rigorous
Disadvantages producing inter-modal • Laser diodes must be used
dispersion making system more
expensive and complicated
power supplies
Larger core diameter makes: Signal power is carried over a
• Better optical coupling single field distribution,
efficiency hence inter-modal dispersion
Advantages • Less errors in splicing is eliminated
• Using LED’s makes system
cheaper, less complicated
and longer life
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Optical Fiber Communications Introduction
Ray Analysis vs. Modal Analysis
Ray Analysis Modal Analysis
Modes are sets of electromagnetic field
If 𝑎 >> 𝜆 ray analysis is fairly
configurations, each satisfies the wave
accurate
equations and boundary conditions
Much simpler to visualize the Gives solutions for both single and
light propagation multimode propagation
Can describe problems of excitation,
Can not describe single mode
detection and coupling between
propagation or field distributions
modes
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Optical Fiber Communications Introduction
Index Difference in Step-index Fibers
𝑛1
𝑛2
𝑛o
𝑛1 − 𝑛2
𝛥≡
𝑛1
𝛥 ≈ 1% − 3% For multimode fibers
For typical
communications fibers 𝛥 ≈ 0.2% − 1% For single mode fibers
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Optical Fiber Communications Introduction
Maximum Acceptance Angle
𝜙′
At the air-core interface
𝑛𝑜
𝑛𝑜 sin𝜃𝑜 = 𝑛1 sin𝜃
= 𝑛1 cos𝜙
At the core-cladding
interface
𝑛1 sin𝜙 = 𝑛2 sin𝜙 ′
𝑛2
Total internal reflection occur when 𝜙 ≥ 𝜙𝑐 = sin−1
𝑛1
Maximum Acceptance Angle = 𝜃𝑜max when 𝜙 = 𝜙𝑐
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Optical Fiber Communications Introduction
Numerical Aperture (NA)
𝜙′
𝑛𝑜 sin𝜃𝑜max = 𝑛1 sin𝜃 = 𝑛1 cos𝜙𝑐
𝑛𝑜
= 𝑛1 1 − sin2 𝜙𝑐
2
𝑛2
= 𝑛1 1−
𝑛1
= 𝑛12 − 𝑛22
Numerical Aperture (NA) = 𝑛𝑜 sin𝜃𝑜max = 𝑛12 − 𝑛22
Show that for 𝛥 << 1 𝑁𝐴 ≅ 𝑛1 2𝛥
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Optical Fiber Communications Introduction
Numerical Aperture & Information Capacity
𝑐 𝛥𝐿
𝜐= =
𝑛1 𝛥 𝑇
c
𝑛1 𝛥 𝐿
𝛥𝑇 = 𝜃𝑜max
𝑐
𝑛1 𝐿
𝛥𝑇max = −𝐿
𝑐 sin𝜙𝑐
𝐿
𝑛1 𝐿 𝑛1 𝑛12 𝐿
𝑛1 − 𝑛2
= −1 =
𝑐 𝑛2 𝑛2 𝑐 𝑛1
𝑛12 𝐿
𝛥 𝑇max = 𝛥
𝑛2 𝑐
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Optical Fiber Communications Introduction
Numerical Aperture & Information Capacity
𝑛12 𝐿
If B is the signal bit rate 𝛥 𝑇max = 𝛥
𝑛2 𝑐
1
𝛥𝑇 < 𝐵𝛥𝑇 < 1
𝐵
𝑛12 𝐿
𝐵 𝛥<1
𝑛2 𝑐
𝑛2 𝑐 𝑛2 𝑐
𝐵𝐿 < 𝐵𝐿 max = 2
𝛥 𝑛12 𝑛1 𝛥
For a system to operate at:
𝐵 𝐿 = 100 𝑀 𝑏Τ𝑠 𝐾𝑚
𝛥 ≈ 2 × 10−3
𝑛1 = 1.5 ≈ 𝑛2
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