unit01_focs.pdf

Fiber Optic
Communication Systems
Dr. Fahim Aziz Umrani
Department of Telecommunication, Room # 213
Institute of Information & Communication Technologies (IICT),
Mehran UET, Jamshoro
https://sites.google.com/a/faculty.muet.edu.pk/fau/focs

Fiber Optic Communication Systems By Dr. Fahim Aziz Umrani
Department of Telecommunication, Mehran UET
Syllabus
Title of Subject : Fiber Optics Communication System Term : (8th Term)
Effective : 01TL-Batch and onwards Marks : Theory (100) Practical (00)
Credit Hours : 4+0 Minimum Contact Hours : 52
Introduction: History of Optical Communication, Optical Fiber Communication System, Advantages of
OFC system.
Optical Fiber Wave Guides: Optical Fiber Waveguide, Ray Theory Transmission, Electromagnetic Mode
Theory for Optical Propagation, Cylindrical Fibers, Single Mode Fiber, Multimode Fibers, Step Index
Fibers, Graded Index Fibers, Single Mode/Multimode fiber transmission characteristics.
Transmission Characteristics: Attenuation, Absorption Losses, Linear Scattering Losses, Non- Linear
Scattering Losses, Fiber Band Loss, Intramodal and Intermodal Dispersion, Overall Fiber Dispersion,
Polarization, Non-Linear Phenomenon.
Optical Fiber Cables and Connectors: Preparation of Optical Fibers, Modified Chemical Vapor
Deposition (MCVD), Optical Fibers, Fiber Strength and Durability, Cable Design, Splicing.
Optical fiber communication system: Components of Fiber Optic Networks, Optical Amplifiers,
Advanced Multiplexing Strategies.
Optical Fiber Measurements: Fiber Attenuation Measurements, Fiber Dispersion Measurements, Field
Measurements.
Recommended Books:
1. Senior J., “Optical Fiber Communications”. Prentice Hall.
2. Rogers A., “Understanding Optical Fiber Communication” Artech House Books.
3. P E Green, “Fiber Optic Networks”, (Prentice Hall, 1993)
4. G P Agrawal, “Fiber-Optic Communication Systems”, (2nd Edition, John Wiley & Sons, 1997)
2

Teaching
Plan
3
Sr. # Topics No. of Lectures required
01 Introduction to the subject, History of Optical Communication 02
02 Optical Fiber Communication System 02
03 Advantages of OFC system 02
04 Optical Fiber Waveguide 02
05 Ray Theory Transmission 02
06 Electromagnetic Mode Theory for Optical Propagation 02
07 Cylindrical Fibers 02
08 Single Mode Fiber, Multimode Fibers, Test 01 02
09 Step Index Fibers, Graded Index Fibers 02
10 Single Mode/Multimode fiber transmission characteristics 02
11 Attenuation, Absorption Losses 02
12 Linear Scattering Losses, Non- Linear Scattering Losses 02
13 Fiber Band Loss, Intramodal and Intermodal Dispersion 02
14 Overall Fiber Dispersion 02
15 Polarization, Non-Linear Phenomenon 02
16 Preparation of Optical Fibers, Modified Chemical Vapor Deposition (MCVD), Test 02 02
17 Optical Fibers, Fiber Strength and Durability 02
18 Cable Design, Splicing 02
19 Components of Fiber Optic Networks 02
20 Optical Amplifiers 02
21 Multimode injection lasers 02
22 Advanced Multiplexing Strategies 02
23 Fiber Attenuation Measurements 02
24 Fiber Dispersion Measurements 02
25 Field Measurements 02
26 Revision of some important topics, Test 03 02
Total Lectures 52

Objectives
 Understand optical fiber propagation characteristics and
transmission properties.
 An understanding of the theory of optical sources including light-
emitting diodes and laser diodes, and the methods for using these
devices in optical fiber communication systems
 Design such fiber optic links and relate the limitations in the
performance to the limitations of the components and subsystems
used;
 Understand the modeling of photo detectors, including shot noise
and avalanche noise.
 Understand optical amplifiers and in particular their noise
characteristics.
 Understanding the principles and methods for constructing optical
fiber communication systems, including techniques to increase the
data rate and decrease transmission impairments.
4

Background of Optical Communications
5
Age of Smoke Signals and semaphores!

Why Optical Communication?
 Optical Fiber is the backbone of modern
communication networks
Voice (SONET/Telephony) - The largest traffic
Video (TV) over Hybrid Fiber Coaxial (HFC)
Fiber Twisted Pair for Digital Subscriber Loops (DSL)
Multimedia (Voice, Data and Video) over DSL or HFC
6
Information revolution wouldn’t have
happened without the Optical Fiber

Information revolution
7

 Physical limits for the bandwidth
Wire ~ 1 MHz = 106 Hz
Coaxial Cable ~ 10 GHz = 1010 Hz
Microwave (Wireless) ~ 100 GHz = 1011 Hz
Optical Fiber ~ 100 THz = 1014 Hz
Free space Optics ~ 1000 THz = 1015 Hz
8

9

 Lowest attenuation  attenuation in the optical fiber (at 1.3 µm
and 1.55 µm bands) is much smaller than electrical attenuation in
any cable at useful modulation frequencies
 Much greater distances are possible without repeaters
 This attenuation is independent of bit rate
 Highest Bandwidth (broadband)  high-speed
 Single Mode Fiber (SMF) offers the lowest dispersion  highest
bandwidth  rich content
 Upgradability: Optical communication system can be upgraded to
higher bandwidth, more wavelengths by replacing only the
transmitters and receivers
 Low Cost for fiber
10

The Nature of Light
 Quantum Theory – Light consists of small
particles (photons)
 Wave Theory – Light travels as a transverse
electromagnetic wave
 Ray Theory – Light travels along a straight line
and obeys laws of geometrical optics. Ray theory
is valid when the objects are much larger than
the wavelength (multimode fibers)
11

Light in History
 Light in Greek Times
 In Greek times many believed that light came from
visible objects toward the eye. However, Plato and
many other Greeks believed that vision issued out
from the eye.
 Empedocles correctly believed that light traveled with
finite speed.
 Aristotle explained rainbows as a sort of reflection off
of raindrops.
 The mathematician Euclid worked with mirrors and
reflection but did not know how to express it
mathematically.
 Ptolemy is the first recorded person to experiment
with optics and collect data, but he believed in Plato's
mistaken thought.
 Light in Arabian Times
 Ptolemy's work was further developed by the
Egyptian scientist Ibn al Haythen, who was known to
Europeans as Alhazen.
 Alhazen who first drew ray diagrams
 The Arabian mathematician Alhazen studied the
refraction of light and disputed the ancient theory
that visual rays emanated from the eye. He believed
that the angles of incidence and refraction are
related, but was unable to determine how they are
related.
 This relationship, now known as Snell's law, was
established six hundred years later.
12

Light in Modern Times
 Many advances in the study of light based on Alhazen work were made in the
16th and 17th centuries by such renowned scientists as Galileo Galilei,
Johannes Kepler, and Renes Descartes.
 The Snell's law was discovered.
 During the late 17th century, a debate grew over whether light behaved as a
particle or a wave. Sir Isaac Newton and Laplace.
 However, there were some who believed in a wave theory of light. The most
notable among these was the Dutch scientist Christiaan Huygens who first
wrote of light as a wave.
 It was not until the early 19th century that the wave theory of light became
widely accepted. This acceptance came in large part due to the work of the
English doctor Thomas Young. (1801, “double-slit experiment”)
 In the 1850s Fizeau and Foucault showed through measurements that light
traveled slower through denser media.
 In the same century, Augustin Fresnel and later James Clerk Maxwell, working
on a wave theory of light explained phenomena such as polarization,
interference, and diffraction. They also determined which part of the light will
be reflected and which transmitted when light is reflected at a surface such as
glass or water.
 Maxwell's work seemed to have finally settled the issue of whether light was a
wave or a particle, but the whole debate was reopened in the 20th century.
 Scientists such as Albert Einstein, who described the Doppler effect for light,
brought the particle theory back into the picture with quantum theory.
 This time they postulated that light did not just behave as a particle or a wave,
but had properties of both.
13

Properties of Light
Definition of light:
That agent, force, or action in nature by the operation of which objects are
rendered visible or luminous. Or light is an electromagnetic radiation that can
produce a visual sensation.
Properties of Light
 Propagation Matter is not required for the propagation of light.
 Reflection occurs at the surface, or boundary, of a regular medium.
 Refraction, or bending, may occur where a change of speed is experienced.
 Interference is found where two waves are superposed.
 Diffraction, or bending around corners, takes place when waves pass the
edges of obstructions.
 Scattering occurs at the surface, or boundary, of irregular medium.
 Absorption change of light into heat energy.
Dual nature of light
 Particle (or Corpuscular) Theory: Sir Isaac Newton believed that light consists
of streams of tiny particles, which he called "corpuscles," emanating from a
luminous source.
 Wave theory: Christian Huygens - The wave theory treats light as a train of
waves having wave fronts perpendicular to the paths of the light rays. Wave
effects are insignificant in an incoherent, large scale optical system because
the light waves are randomly distributed and there are plenty of photons.
14

The Electromagnetic Theory
 The James Clerk Maxwell in 1865 predicted that heat, light, and electricity are
propagated in free space at the speed of light as electromagnetic disturbances.
15

The Electromagnetic Spectrum
 EM-Spectrum extend from 10 Hz to 1025 Hz.
 All EM radiations travel in free space with constant velocity of 3 x 108 m/s.
 Optical radiation lies between radio waves and x-rays on the spectrum.
16

Department of Telecommunication, Mehran UET 17

Visible Spectrum/Visible Light
 At x-ray and shorter wavelengths, electromagnetic radiation tends to be
quite particle like in its behavior, whereas toward the long wavelength end
of the spectrum the behavior is mostly wavelike. The visible portion
occupies an intermediate position, exhibiting both wave and particle
properties in varying degrees.
 Their wave lengths range from approximately 7600 A to 4000 A.
 The optical spectrum also extends into the near infrared and into the near
ultraviolet. Although our eyes cannot see these radiations, they can be
detected by means of photographic film.
18

Ultraviolet (UV) light
 UV-A (or black light) is the least harmful and most
commonly found type of UV light, because it has the
least energy. It is used for its relative harmlessness and
its ability to cause fluorescent materials to emit visible
light - thus appearing to glow in the dark. Most
phototherapy and tanning booths use UV-A lamps.
 UV-B is typically the most destructive form of UV light,
because it has enough energy to damage biological
tissues, yet not quite enough to be completely
absorbed by the atmosphere. UV-B is known to cause
skin cancer. Since most of the extraterrestrial UV-B light
is blocked by the atmosphere, a small change in the
ozone layer could dramatically increase the danger of
skin cancer.
 Short wavelength UV-C is almost completely absorbed
in air within a few hundred meters. When UV-C
photons collide with oxygen atoms, the energy
exchange causes the formation of ozone. UV-C is almost
never observed in nature, since it is absorbed so
quickly. Germicidal UV-C lamps are often used to purify
air and water, because of their ability to kill bacteria.
19
Common UV band designations
Short wavelength UV light exhibits more quantum properties than its visible and infrared
counterparts. UV light is arbitrarily broken down into three bands:

Infrared (IR) Light
 Infrared light contains the least amount of energy per photon of any other band and
therefore, an IR photon often lacks the energy required to pass the detection
threshold of a quantum detector. IR is usually measured using a thermal detector such
as a thermopile, which measures temperature change due to absorbed energy.
 Since heat is a form of infrared light, far infrared detectors are sensitive to
environmental changes - such as a person moving in the field of view. Night vision
equipment takes advantage of this effect, amplifying infrared to distinguish people and
machinery that are concealed in the darkness.
 Infrared is unique in that it exhibits primarily wave properties. This can make it much
more difficult to manipulate than UV and visible light. IR is more difficult to focus with
lenses, refracts less, diffracts more, and is difficult to diffuse.
20

The most important ideas
The most important ideas to note are:
 Light travel slower through denser media.
 Propagation Matter is not required for the propagation of light.
 Reflection occurs at the surface, or boundary, of a regular medium.
 Refraction, or bending, may occur where a change of speed is
experienced.
 Interference is found where two waves are superposed.
 Diffraction, or bending around corners, takes place when waves pass the
edges of obstructions.
 Scattering occurs at the surface, or boundary, of irregular medium.
 Absorption change of light into heat energy.
 Electromagnetic waves span over many orders of magnitude in
wavelength (or frequency).
 The frequency of the electromagnetic radiation is inversely proportional to
the wavelength.
 The visible spectrum is a very small part of the electromagnetic spectrum.
 Photon energy increases as the wavelength decreases. The shorter the
wavelength, the more energetic are its photons.
21

Wavelength Standards
 Frequency multiples of 50 GHz or 100 GHz
 λ = c/f c = 299792458 m/s
 λ [nm] = 299792.458/f [THz]
f = 195 THz → λ = 1537.397 nm
f =195.1 THz → λ = 1536.609 nm
f =195.2 THz → λ = 1535.822 nm
f =193.4 THz → λ = 1550.116 nm
22
f
50 or 100 GHz ITU grid

Wavelength Ranges available for
Communication
23
Band Name Range
O-band Original 1260 – 1360 nm
E-Band Extended 1360 – 1460 nm
S-Band Short 1460 – 1530 nm
C-Band Conventional 1530 – 1565 nm
L-Band Long 1565 – 1625 nm
U-Band Ultra-long 1625 – 1675
Different types of sources/detectors/amplifiers are used in
different bands

Example of a Problem
How many 100 GHz-ITU Grid channels are covered by the conventional band (1530 –
1560 nm)?
λ = 1530 nm → f = 195.943 THz
λ = 1560 nm → f = 192.174 THz
192.2
192.3
192.4
.
.
.
195.7
195.8
195.9
24
38
1
37
1
1
.
0
2
.
192
9
.
195






N

Fiber Optic Communication System
25
 Generic System
 Transmitter and receiver module
 Fiber-optic communication channel

OFC System
 An optical fiber communication (OFC) system is similar
in basic concept to any type of communication system,
the function of which is to convey the signal from the
information source over the transmission medium, to
the destination.
 For OFC, the information source (usually, an LED or
laser) provides an electrical signal to a transmitter
comprising an electrical stage which drives an optical
source to give modulation of the light wave carrier.
 The transmission medium consists of an optical fiber
cable and the receiver consists of an optical detector
which drives a further electrical stage and hence
provides demodulation of the optical carrier.
 Photodiodes (p-n, p-i-n, or avalanche) and, in some
instances, phototransistors and photoconductors are
used as detectors.
26

Networks
 Local area networks (LAN) L ≤ 1 km
 Metropolitan area networks (MAN) L ≤ 10 km
 Wide area networks (WAN) L ≥ 100 km
 LAN: provides communication access to users. Bit-rate
requirement is relatively low. Main issue: scalable and
reconfigurable architecture.
 MAN: provides communication access within a city.
Moderate Bit-rate requirements. Fixed architecture
acceptable in many access
 WAN: provides communication over long distances. High-bit
rate is required. Use of multiplexing techniques.
Compensation for optical losses and dispersion is
major problem.
27

First Generation Fiber Optic Systems
Purpose:
 Eliminate repeaters in T-1 systems used in inter-office trunk lines
Technology:
 0.8 µm GaAs semiconductor lasers
 Multimode silica fibers
 All the switching and processing is handled by electronics
Limitations:
 Fiber attenuation
 Intermodal dispersion
Deployed since 1974
 Examples
 SONET (synchronous optical network), USA
 SDH (synchronous digital hierarchy), international
 FDDI (Fiber distributed data network)
28

Second Generation Fiber Optic Systems
Opportunity:
 Development of low-attenuation fiber (removal of H2O and
other impurities)
 Eliminate repeaters in long-distance lines
Technology:
 Use optics for switching and routing
 1.3 µm multi-mode semiconductor lasers
 Single-mode, low-attenuation silica fibers
 DS-3 signal: 28 multiplexed DS-1 signals carried at 44.736
Mbps
Limitation:
 Fiber attenuation (repeater spacing ≈ 6 km)
Deployed since 1978
29

Third Generation Fiber Optic Systems
Opportunity:
 Deregulation of long-distance market
Technology:
 1.55 µm single-mode semiconductor lasers
 Single-mode, low-attenuation silica fibers
 OC-48 signal: 810 multiplexed 64-kb/s voice channels
carried at 2.488 Gbps
Limitations:
 Fiber attenuation (repeater spacing ≈ 40 km)
 Fiber dispersion
Deployed since 1982
30

Fourth Generation Fiber Optic Systems
Opportunity:
 Development of erbium-doped fiber amplifiers (EDFA)
Technology (deployment began in 1994):
 1.55 µm single-mode, narrow-band semiconductor lasers
 Single-mode, low-attenuation, dispersion-shifted silica fibers
 Wavelength-division multiplexing of 2.5 Gb/s or 10 Gb/s signals
Nonlinear effects limit the following system parameters:
 Signal launch power
 Propagation distance without regeneration/re-clocking
 WDM channel separation
 Maximum number of WDM channels per fiber
Polarization-mode dispersion limits the following parameters:
 Propagation distance without regeneration/re-clocking
31

Evolution of Optical Networks
32
1.55 μm
DFB Laser
Receiver
0.85 LED
or LD
Receiver
Regenerators/repeaters
Multimode fibers
1.3 μm
FP Laser
Receiver
Single mode fibers
T3
T2
T1
MUX
DEMUX
T3
T2
T1
Single mode fibers
Optical amplifiers

History of Attenuation
33

Three windows based on Wavelengths
34

Multiplexing Technologies
 Time division multiplexing
35
Low-speed data streams
High-speed data streams
Bit rate 10 to 40 Gbps

Wavelength Division Multiplexing
36
MUX
λ1
λN
λ3
λ2
λ1 λN
λ3
λ2
.
.
...
Essentially the same as
frequency division
multiplexing
WDM: 32 wavelengths, 2.5 Gbps each → 80 Gbps commercially
available now.
Combination of WDM and TDM demonstrated to provide 2 Tbps
over single mode fiber

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