Optical communication system

Introduction to Optical
Communication system
BY: ENG. MOHAMED HAMDY NAEEM
SUPERVISOR: DR.MOSTAFA FEDAWAY
COURSE PHOTONICS DEVICES E414
E414

1-OPTICAL COMMUNICATION SYSTEM OVERVIEW
2-HISTORYAND MATHEMATICS OF OPTICAL COMMUNICATION
3-SYSTEM CONSTRUCTIONIN DETAIL
I-CABLE CONSTRUCTIONAND OPTICAL FIBER TYPES
II-TRANSCEIVER CONSTRUCTION
III-OPTICALAMPLIFIER
4-APPLICATIONS OF THE OPTICAL COMMUNICATION SYSTEM
5-COMMISSIONINGAND EXTENSIONOF OPTICAL FIBER CABLE
6-CABLE SPLICING
7-TESTAND MEASURES
8-CONCLUSION
By: Eng. Mohamed Hamdy Naeem
Contents

OPTICAL COMMUNICATION SYSTEM OVERVIEW
Transmission
channel
Tx
E
O
Rx
O
E
ReceiverConverterTransmitter Converter
Optical Fiber
Section
Optical
Amplifier
Wavelength(nm)

2-History and Math of optical communication
A Short History of Optical Telecommunications
Circa 2500 B.C. Earliest known glass
Roman times-glass drawn into fibers
Venice Decorative Flowers made of glass fibers
1609-Galileo uses optical telescope
1626-Snell formulates law of refraction
1668-Newton invents reflection telescope
1840-Samuel Morse Invents Telegraph
1841-Daniel Colladon-Light guiding demonstrated
in water jet
1870-Tyndall observes light guiding in a thin water jet
1873-Maxwell electromagnetic waves
1876-Elisha Gray and Alexander Bell Invent Telephone
1877-First Telephone Exchange
1880-Bell invents Photophone
1888-Hertz Confirms EM waves and relation to light
1880-1920 Glass rods used for illumination
1897-Rayleigh analyzes waveguide
1899-Marconi Radio Communication
1902-Marconi invention of radio detector
1910-1940 Vacuum Tubes invented and developed
1930-Lamb experiments with silica fiber
1931-Owens-Fiberglass
1936-1940 Communication using a waveguide
1876-Alexander Graham Bell
1876 First commercial Telephone
1970 I. Hayashi
Semiconductor Laser

1951-Heel, Hopkins, Kapany image transmission using fiber
bundles
1957-First Endoscope used in patient
1958-Goubau et. al. Experiments with the lens guide
1958-59 Kapany creates optical fiber with cladding
1960-Ted Maiman demonstrates first laser in Ruby
1960-Javan et. al. invents HeNe laser
1962-4 Groups simultaneously make first semiconductor
lasers
1961-66 Kao, Snitzer et al conceive of low loss single mode
fiber communications and develop theory
1970-First room temp. CW semiconductor laser-Hayashi &
Panish
April 1977-First fiber link with live telephone traffic-
GTE Long Beach 6 Mb/s
May 1977-First Bell system 45 mb/s links
GaAs lasers 850nm Multimode -2dB/km loss
Early 1980s-InGaAsP 1.3 µm Lasers
- 0.5 dB/km, lower dispersion-Single mode
Late 1980s-Single mode transmission at 1.55 µm -0.2
dB/km
1989-Erbium doped fiber amplifier
1 Q 1996-8 Channel WDM
4th Q 1996-16 Channel WDM
1Q 1998-40 Channel WDM

Bells Photophone
1880 - Photophone
Transmitter
1880 - Photophone Receiver
“The ordinary man…will find a little difficulty in comprehending how sunbeams are to be used. Does Prof. Bell intend to
connect Boston and Cambridge…with a line of sunbeams hung on telegraph posts, and, if so, what diameter are the
sunbeams to be…?…will it be necessary to insulate them against the weather…?…until (the public) sees a man going through
the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general
feeling that there is something about Prof. Bell’s photophone which places a tremendous strain on human credulity.”
New York Times Editorial, 30 August 1880

History
mm wave guide versus
optical fiber
First successfully drawn
fiber with a loss of 20
dB/km 1970
Soon thereafter loss reaches
almost the same level as
modern fiber
Next major achievement: RT
CW operating diode laser in
1970. Wavelength was 850 nm
1970-1971 – all the
components of a fiber
optics link were available

History
• Data transmission in 1960 – MW radio links
Bandwidth limitations of
radio links lead to
development of mm wave
metalic waveguides
Charlie kau 1966
low loss fiber
2009 Nobel Prize

Approaches to Optical Communication

Increase in Bitrate-Distance product
Agrawal-Fiber Optic Communications

Progress In Lightwave Communication
Technology

The Internet
From: www.caida.org

13
3. optical
window
Infrared
range
Visible
range
Singlemode
(1310 – 1650nm)
GOF Multimode
(850 – 1300nm)
POF
(520 – 650nm)
PCF
(650 – 850nm)
1. optical
window
1800 1600 1400 1200 1000 800 600 400
Wavelength [nm]
2. optical
window
Wavelength range of optical
transmission

• Light
– Ultraviolet (UV)
– Visible
– Infrared (IR)
• Communication wavelengths
– 850, 1310, 1550 nm
– Low-loss wavelengths
• Specialty wavelengths
– 980, 1480, 1625 nm
UV IR
Visible
850 nm
980 nm
1310 nm
1480 nm
1550 nm
1625 nm
l
125 GHz/nm
Wavelength: l (nanometers)
Frequency:  (terahertz)
C = x l
Optical Spectrum

Optical Spectrum
• Light
– Ultraviolet (UV)
– Visible
– Infrared (IR)
• Communication wavelengths
– 850 nm Multimode
–1310 nm Singlemode
–1550 nm DWDM & CWDM
• Specialty wavelengths
– 980, 1480, 1625 nm (e.g. Pump
Lasers)
UV IR
Visible
850 nm
980 nm
1,310 nm
1,480 nm
1,550 nm
1,625 nm
l
125 GHz/nm
Wavelength: l (nanometres)
Frequency:  (Terahertz)
c = l

16
Multi-Mode vs Single-Mode
Multi-Mode Single-Mode
Modes of light Many One
Distance Short Long
Bandwidth Low High
Typical
Application
Access Metro, Core

17
Velocity of electromagnetic wave
Speed of light (electromagnetic radiation) is:
C0 = Wavelength x frequency
C0 = 299793 km / s
Remarks: An x-ray-beam (l = 0.3 nm), a radar-beam (l = 10 cm ~ 3 GHz) or
an infrared-beam (l = 840 nm) have the same velocity in vacuum
(Speed of light in vacuum)

18
Refractive index
(Change of velocity of light in matter)
Velocity of light (electromagnetic radiation) is:
always smaller than in vacuum, it is
Cn (Velocity of Light in Matter)
n = C0 / Cn
n is defined as refractive index (n = 1 in Vacuum)
n is dependent on density of matter and wavelength
Remarks: nAir= 1.0003; ncore= 1.5000 or nssugar Water= 1.8300

19
Refraction
light beam
a1
a2Glass material
with slightly
higher density Glass material
with slightly
lower density
n2
n1
Remarks: n1 < n2 and a1 > a2
sin a2 / sin a1 = n1 / n2
Plane of interface

20
Total refraction
light beam
a1 = 90°
aLGlass material
with slightly
higher density
Glass material
with slightly
lower density
n2
n1
Remarks: n1 < n2 and a2 = aL
Critical angle
sin a1 = 1 sin aL = n1 / n2
Plane of interface
Incident light has angle = critical

Total internal Reflection

22
Transmission Bands
 Optical transmission is conducted in wavelength
regions, called “bands”.
 Commercial DWDM systems typically transmit at
the C-band
• Mainly because of the Erbium-Doped Fiber
Amplifiers (EDFA).
 Commercial CWDM systems typically transmit at
the S, C and L bands.
 ITU-T has defined the wavelength grid for xWDM
transmission
• G.694.1 recommendation for DWDM
transmission, covering S, C and L bands.
• G.694.2 recommendation for CWDM
transmission, covering O, E, S, C and L bands.
Band Wavelength (nm)
O 1260 – 1360
E 1360 – 1460
S 1460 – 1530
C 1530 – 1565
L 1565 – 1625
U 1625 – 1675

23
Reflection
light beam
ain
Glass material
with slightly
lower density
n2
n1
Remarks: n1 < n2 and ain = aout
aout
Glass material
with slightly
higher density
Plane of interface
Incident light has angle > critical

24
Summary
n2
aout
Glass material
with slightly
lower density
ain Glass material
with slightly
higher density
n1
a2a2
a1 90
refraction
Total
refraction
reflection
Plane of Interface

25
Numerical Aperture (NA)
Light rays outside acceptance
angle leak out of core
NA = (n2
2 – n2
1) = sin  Standard SI-POF = NA 0.5 → 30°
Low NA SI-POF = NA 0.3 → 17.5°

3-system construction in detail
Optical Fiber
Section
Optical
Amplifier
Wavelength(nm)
Optical Fiber
Section
Optical Amplifier

Optical fibers
Made by drawing molten glass from
a crucible
1965: Kao and Hockham proposed
fibers for broadband communication
1970s: commercial methods of
producing low-loss fibers by
Corning and AT&T.
1990: single-mode fiber,
capacity 622 Mbit/s
Now: capacity ~ 1Tbit/s, data rate
10 Gbit/s

I.Optical Fiber Cable
How Does fiber optic transmit light

I. Optical Fiber Cable
Fiber structure
Primary Coating (protection)
Cladding
Core (denser material, higher N/A)
Light entrance
cone N.A.
(Numerical Aperture)
n1
n1
n2
Refractive index
profile
n1 n2

Fiber-optic cable
 Use light transmissions
 EMI, crosstalk and attenuation become no issue.
 Well suited for data, video and voice
transmissions
 Most secure of all cable media
 Installation and maintenance procedures require
skills
 Cost of cable
 Cost of retrofitting of existing network equipment
because incompatible with most electronic
network equipment

Fiber-optic cable
• Single mode fiber:
– A single direct bean of light, allowing for
greater distances and increased transfer
speeds.
• Multimode fiber:
– Many beams of light travel through the cable
– This strategy weakens the signal, reducing
the length and speed the data signal can
travel.

Fiber-optic cable
n2
n1
Cladding
Core
n2
n1
Cladding
Core
• Multimode fiber
–Core diameter varies
• 50 mm for step index
• 62.5 mm for graded index
–Bit rate-distance product
>500 MHz-km
• Single-mode fiber
–Core diameter is about 9 mm
–Bit rate-distance product
>100 THz-km

• SMF-28(e) (standard, 1310 nm optimized, G.652)
– Most widely deployed so far, introduced in 1986, cheapest
• DSF (Dispersion Shifted, G.653)
– Intended for single channel operation at 1550 nm
• NZDSF (Non-Zero Dispersion Shifted, G.655)
– For WDM operation, optimized for 1550 nm region
– TrueWave, FreeLight, LEAF, TeraLight…
– Latest generation fibers developed in mid 90’s
– For better performance with high capacity DWDM systems
– MetroCor, WideLight…
– Low PMD ULH fibers
Types of Single-Mode Fiber

Fiber-optic connectors
MIC, Standard FDDI
connector
FC
LC
SC duplex
ST
SC
There are a variety of connectors and several ways of
Connecting these connectors, such bayonet, snap-lock,
and push-pull connectors. A couple here:

Wavelength Division Multiplexed (WDM)
Long-Haul Optical Fiber Transmission System
Transmitter
Transmitter
Transmitter
Receiver
Receiver
Receiver
M
U
X
D
E
M
U
XOptical Amplifier
l1
l2
l3
WDM “Routers” Erbium/Raman Optical Amplifier

Categorizing Optical Networks
Who Uses it? Span (km) Bit Rate
(bps)
Multi-plexing Fiber Laser Receiver
Core/
LongHaul
Phone Company,
Gov’t(s)
~103 ~1011
(100’s of
Gbps)
DWDM/TDM SMF/ DCF EML/ DFB APD
Metro/
Regional
Phone Company, Big
Business
~102 ~1010
(10’s of Gbps)
DWDM/CWDM
/TDM
SMF/ LWPF DFB APD/ PIN
Access/
LocalLoop
Small Business,
Consumer
~10 ~109
(56kbps-
1Gbps)
TDM/ SCM/ SMF/ MMF DFB/ FP PIN
DWDM: Dense Wavelength Division Multiplexing (<1nm spacing)
CWDM: Coarse Wavelength Division Multiplexing (20nm spacing)
TDM: Time Division Multiplexing (e.g. car traffic)
SCM: Sub-Carrier Multiplexing (e.g. Radio/TV channels)
SMF: Single-Mode Fiber (core~9mm)
MMF: Multi-Mode Fiber (core~50mm)
LWPF: Low-Water-Peak Fiber
DCF: Dispersion Compensating Fiber
EML: Externally modulated (DFB) laser
DFB: Distributed Feedback Laser
FP: Fabry-Perot Laser
APD: Avalanche Photodiode
PIN: p-i-n Photodiode

Optical Fiber Attributes
Attenuation: Due to Rayleigh scattering and chemical absorptions,
the light intensity along a fiber decreases with
distance. This optical loss is a function of wavelength
(see plot).
Dispersion: Different colors travel at different speeds down the
optical fiber. This causes the light pulses to spread
in time and limits data rates.
Types of Dispersion
Chromatic Dispersion is caused mainly by the
wavelength dependence of the index of
refraction (dominant in SM fibers)
Modal Dispersion arises from the differences in
group velocity between the “modes” travelling
down the fiber (dominant in MM fibers)
t
t t
t


launch
receive

Optical Fiber Attributes continue
Attenuation:
Reduces power level with distance
Dispersion and Nonlinearities:
Erodes clarity with distance and speed
Signal detection and recovery is an analog problem
Analog Transmission Effects

• Polarization Mode Dispersion (PMD)
Single-mode fiber supports two polarization states
Fast and slow axes have different group velocities
Causes spreading of the light pulse
• Chromatic Dispersion
Different wavelengths travel at different speeds
Causes spreading of the light pulse
Types of Dispersion

• Affects single channel and DWDM systems
• A pulse spreads as it travels down the fiber
• Inter-symbol Interference (ISI) leads to
performance impairments
• Degradation depends on:
– laser used (spectral width)
– bit-rate (temporal pulse separation)
– Different SM types
Interference
A Snapshot on Chromatic Dispersion

60 Km SMF-28
4 Km SMF-28
10 Gbps
40 Gbps
Limitations From Chromatic
Dispersion
t
t
• Dispersion causes pulse distortion,
pulse "smearing" effects
• Higher bit-rates and shorter pulses are less robust
to Chromatic Dispersion
• Limits "how fast“ and “how far”

Combating Chromatic Dispersion
• Use DSF and NZDSF fibers
– (G.653 & G.655)
• Dispersion Compensating Fiber
• Transmitters with narrow spectral width

Dispersion Compensating Fiber
• Dispersion
Compensating Fiber:
– By joining fibers with CD of opposite signs
(polarity) and suitable lengths an average
dispersion close to zero can be obtained;
the compensating fiber can be several
kilometers and the reel can be inserted at
any point in the link, at the receiver or at the
transmitter

Dispersion Compensation
Transmitter
Dispersion
Compensators
Dispersion Shifted Fiber Cable
+100
0
-100
-200
-300
-400
-500
CumulativeDispersion(ps/nm)
Total Dispersion Controlled
Distance from
Transmitter (km)
No Compensation
With Compensation

How Far Can I Go Without Dispersion?
Distance (Km) =
Specification of Transponder (ps/nm)
Coefficient of Dispersion of Fiber (ps/nm*km)
A laser signal with dispersion tolerance of 3400 ps/nm
is sent across a standard SMF fiber which has a Coefficient of
Dispersion of 17 ps/nm*km.
It will reach 200 Km at maximum bandwidth.
Note that lower speeds will travel farther.

Non-Linear Effects in Fibers
Self-Phase Modulation: When the optical power of a pulse is
very high, non-linear polarization terms
contribute and change the refractive
index, causing pulse spreading and delay.
Four-wave Mixing: Non-linearity of fiber can cause ‘mixing’
of nearby wavelengths causing
interference in WDM systems.
Stimulated Brillouin
Scattering: Acoustic Phonons create sidebands that
can cause interference.
Cross-Phase Modulation: Same as SPM, except involving more than
one WDM channel, causing cross-talk
between channels as well.

Technology Trends
850nm & 1310nm  Preferred by high-volume,
moderate performance
data comm manufacturers
1310nm & 1550nm  Preferred by high performance
but lower volume (today)
telecomm manufacturers
Reason? You need lots of them, they don’t need to go far,
and you’re not using enough fiber ($) to justify wavelength
division multiplexing (WDM), I.e. low-quality lasers are OK.
Reason? You don’t need lots, but they have to be good
enough to transmit over long distances… cost of fiber (and
TDM) justifies WDM… 1550nm is better for WDM

DFB vs. FP laser
Simple FP
mirror
gain
cleave
+
- mirror
gain
AR coating
+
-
Etched
grating
l l
DFB
FP: • Multi-longitudinal Mode
operation
• Large spectral width
• high output power
• Cheap
DFB: • Single-longitudinal Mode
operation
• Narrow spectral width
• lower output power
• expensive

Structure of WDM MUX/DEMUX
(Arrayed Waveguide Grating)
(100) Si
B,P-doped v-SiO2
Thermal v-SiO2
P-doped v-SiO2 core
} core layer
TM, sy
TE, sx
Input
waveguides
Output
waveguides
Arrayed
waveguides Star coupler

The 3 “R”s of Optical Networking
A Light Pulse Propagating in a Fiber Experiences 3 Type of Degradations:
Loss of Energy
Loss of Timing (Jitter)
(From Various Sources) t
ts Optimum
Sampling Time
t
ts Optimum
Sampling Time
Phase Variation
Shape Distortion
Pulse as It Enters the Fiber Pulse as It Exits the Fiber

Re-Shape DCU
The 3 “R”s of Optical Networking (Cont.)
The Options to Recover the Signal from Attenuation/Dispersion/Jitter
Degradation Are:
Pulse as It Enters the Fiber Pulse as It Exits the Fiber
Amplify to Boost the Power
t
ts Optimum
Sampling Time
t
ts Optimum
Sampling Time
Phase Variation
Re-Generate
O-E-O
Re-gen, Re-shape and
Remove Optical Noise
t
ts Optimum
Sampling Time
Phase Re-Alignment

Increasing Network Capacity Options
Faster Electronics
(TDM)
Higher bit rate, same fiber
Electronics more expensive
More Fibers
(SDM)
Same bit rate, more fibers
Slow Time to Market
Expensive Engineering
Limited Rights of Way
Duct Exhaust
W
D
M
Same fiber & bit rate, more ls
Fiber Compatibility
Fiber Capacity Release
Fast Time to Market
Lower Cost of Ownership
Utilizes existing TDM Equipment

Single
Fiber (One
Wavelength)
Channel 1
Channel n
Single Fiber
(Multiple
Wavelengths)
l1
l2
ln
Fiber Networks
• Time division multiplexing
– Single wavelength per fiber
– Multiple channels per fiber
– 4 OC-3 channels in OC-12
• Wave division multiplexing
– Multiple wavelengths per fiber
– 4, 16, 32, 64 channels
per system
– Multiple channels per fiber

DS-1
DS-3
OC-1
OC-3
OC-12
OC-48
OC-12c
OC-48c
OC-192c
Fiber
DWDM
OADM
SONET
ADM
Fiber
TDM and DWDM Comparison
• TDM (SONET/SDH)
– Takes sync and async signals
and multiplexes them to a
single higher optical bit rate
– E/O or O/E/O conversion
• (D)WDM
– Takes multiple optical
signals and multiplexes
onto a single fiber
– No signal format conversion

DWDM History
• Early WDM (late 80s)
– Two widely separated wavelengths (1310, 1550nm)
• “Second generation” WDM (early 90s)
– Two to eight channels in 1550 nm window
– 400+ GHz spacing
• DWDM systems (mid 90s)
– 16 to 40 channels in 1550 nm window
– 100 to 200 GHz spacing
• Next generation DWDM systems
– 64 to 160 channels in 1550 nm window
– 50 and 25 GHz spacing

TERM
TERM
TERM
Conventional TDM Transmission—10 Gbps
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
40km
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
120 km
OC-48
OA OAOA OA
120 km 120 km
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
DWDM Transmission—10 Gbps
1 Fiber Pair
4 Optical Amplifiers
Why DWDM—The Business Case
TERM
4 Fibers Pairs
32 Regenerators
40km 40km 40km 40km 40km 40km 40km 40km

Drivers of WDM Economics
• Fiber underground/undersea
– Existing fiber
• Conduit rights-of-way
– Lease or purchase
• Digging
– Time-consuming, labor intensive, license
– $15,000 to $90,000 per Km
• 3R regenerators
– Space, power, OPS in POP
– Re-shape, re-time and re-amplify
• Simpler network management
– Delayering, less complexity, less elements

• Transparency
– Can carry multiple protocols on same fiber
– Monitoring can be aware of multiple protocols
• Wavelength spacing
– 50GHz, 100GHz, 200GHz
– Defines how many and which wavelengths can be used
• Wavelength capacity
– Example: 1.25Gb/s, 2.5Gb/s, 10Gb/s
0 50 100 150 200 250 300 350 400
Characteristics of a WDM Network
Wavelength Characteristics

Optical Transmission Bands
Band Wavelength (nm)
820 - 900
1260 – 1360
“New Band” 1360 – 1460
S-Band 1460 – 1530
C-Band 1530 – 1565
L-Band 1565 – 1625
U-Band 1625 – 1675

ITU Wavelength Grid
• ITU-T l grid is based on 191.7 THz + 100 GHz
• It is a standard for laser in DWDM systems
l1530.33 nm 1553.86 nm
0.80 nm
195.9 THz 193.0 THz
100 GHz
Freq (THz) ITU Ch Wave (nm) 15201/252 15216 15800 15540 15454
192.90 29 1554.13 x x x x x
192.85 1554.54
192.80 28 1554.94 x x x x x
192.75 1555.34
192.70 27 1555.75 x x x x x
192.65 1556.15
192.60 26 1556.55 x x x x x

What is DWDM?
 It transmits multiple data signals using different wavelengths of light
through a single fiber.
 Incoming optical signals are assigned to specific frequencies within a
designated frequency band.
 The capacity of fiber is increased when these signals are multiplexed
onto one fiber
 Transmission capabilities is 4-8 times of TDM Systems with the help of
Erbium doped optical amplifier.
 EDFA’s : increase the optical signal and don’t have to regenerate signal
to boost it strength.
 It lengthens the distances of transmission to more than 300 km before
regeneration .

Ability to put multiple services onto a single
wavelength
Characteristics of a WDM Network
Sub-wavelength Multiplexing or MuxPonding

Why DWDM?
The Technical Argument
• DWDM provides enormous amounts of scaleable
transmission capacity
– Unconstrained by speed of
available electronics
– Subject to relaxed dispersion and nonlinearity tolerances
– Capable of graceful capacity growth

Optical Multiplexer
Optical De-multiplexer
Optical Add/Drop Multiplexer
(OADM)
Transponder
DWDM Components
l1
l2
l3
l1
l2
l3
850/1310 15xx
l1
l2
l3
l1...n
l1...n

Optical Amplifier
(EDFA)
Optical Attenuator
Variable Optical Attenuator
Dispersion Compensator (DCM / DCU)
More DWDM Components

VOA EDFA DCM
VOAEDFADCM
Service Mux
(Muxponder)
Service Mux
(Muxponder)
DWDM SYSTEM DWDM SYSTEM
Typical DWDM Network Architecture

Transponders
• Converts broadband optical signals to a specific wavelength via
optical to electrical to optical conversion (O-E-O)
• Used when Optical LTE (Line Termination Equipment) does not have
tight tolerance ITU optics
• Performs 2R or 3R regeneration function
• Receive Transponders perform reverse function
Low Cost
IR/SR Optics
Wavelengths
Converted
l1
From Optical
OLTE
To DWDM MuxOEO
OEO
OEO
l2
ln

Performance Monitoring
• Performance monitoring performed on a
per wavelength basis through transponder
• No modification of overhead
– Data transparency is preserved

Laser Characteristics
l
lcPower
l
Power lc
DWDM Laser
Distributed Feedback (DFB)
Active medium
Mirror
Partially transmitting
Mirror
Amplified light
Non DWDM Laser
Fabry Perot
• Spectrally broad
• Unstable center/peak wavelength • Dominant single laser line
• Tighter wavelength control

DWDM Receiver Requirements
• Receivers Common to all Transponders
• Not Specific to wavelength (Broadband)
I

72
Why the Need for Optical Amplification?
• Semiconductor devices can convert an optical signal into an
electrical signal, amplify it and reconvert the signal back to an
optical signal. However, this procedure has several disadvantages:
– Costly
– Require a large number over long distances
– Noise is introduced after each conversion in analog signals
(which cannot be reconstructed)
– Restriction on bandwidth, wavelengths and type of optical
signals being used, due to the electronics
• By amplifying signal in the optical domain many of these
disadvantages would disappear!

73
Optical Amplification
• Amplification gain: Up to a factor of 10,000 (+40 dB)
• In WDM: Several signals within the amplifier’s gain (G)
bandwidth are amplified, but not to the same extent
• It generates its own noise source known as Amplified
Spontaneous Emission (ASE) noise.
Optical
Amplifier
(G)
Weak signal
Pin
Amplified signal
Pout
ASE ASE
Pump Source

74
Optical Amplification - Spectral Characteristics
Wavelength
Power
(unamplifiedsignal)
Wavelength
Power
(amplifiedsignal)
ASE
Wavelength
Power
(unamplifiedsignal)
Wavelength
Power
(amplifiedsignal)
ASE
Single channel
WDM channels

75
Optical Amplification - Noise Figure
• Required figure of merit to compare
amplifier noise performance
• Defined when the input signal is coherent
)(rationoisetosignalOutput
)(rationoisetosignalInput
(NF)FigureNoise
o
i
SNR
SNR



NF is a positive number, nearly always > 2 (I.e. 3 dB)
Good performance: when NF ~ 3 dB
NF is one of a number of factors that determine the
overall BER of a network.

76
Optical Amplifiers - Types
There are mainly two types:
• Semiconductor Laser (optical) Amplifier
(SLA) (SOA)
• Active-Fibre or Doped-Fibre
– Erbium Doped Fibre Amplifier (EDFA)
– Fibre Raman Amplifier (FRA)
– Thulium Doped Fibre Amplifier (TDFA)

Optical Amplifier
Pout = GPinPin
• EDFA amplifiers
• Separate amplifiers for C-band and L-band
• Source of optical noise
• Simple
G

OA Gain
Typical
Fiber Loss
4 THz
25 THz
OA Gain and Fiber Loss
• OA gain is centered in 1550 window
• OA bandwidth is less than fiber bandwidth

Erbium Doped Fiber Amplifier
“Simple” device consisting of four parts:
• Erbium-doped fiber
• An optical pump (to invert the population).
• A coupler
• An isolator to cut off backpropagating noise
Isolator Coupler IsolatorCoupler
Erbium-Doped
Fiber (10–50m)
Pump
Laser
Pump
Laser

Optical Signal-to Noise Ratio (OSNR)
• Depends on :
Optical Amplifier Noise Figure:
(OSNR)in = (OSNR)outNF
• Target : Large Value for X
Signal Level
Noise Level
X dB
EDFA Schematic
(OSNR)out(OSNR)in
NF
Pin

Loss Management: Limitations
Erbium Doped Fiber Amplifier
• Each amplifier adds noise, thus the optical
SNR decreases gradually along the chain; we
can have only have a finite number of
amplifiers and spans and eventually electrical
regeneration will be necessary
• Gain flatness is another key parameter mainly
for long amplifier chains
Each EDFA at the Output Cuts at Least in a Half
(3dB) the OSNR Received at the Input
Noise Figure > 3 dB
Typically between 4 and 6

l1,l2,l3,...ln
l2
l1, ,l3,...ln
Dielectric Filter
• Well established technology, up to 200 layers
Optical Filter Technology

Multiplexer / Demultiplexer
Wavelengths
Converted via
Transponders
Wavelength
Multiplexed
Signals
DWDM
Mux
DWDM
Demux
Wavelength
Multiplexed
Signals
Wavelengths
separated into
individual ITU
Specific
lambdas
Loss of power for each Lambda

Optical Add/Drop Filters (OADMs)
OADMs allow flexible add/drop of channels
Drop
Channel
Add
Channel
Drop &
Insert
Pass Through loss and Add/Drop loss

Optical Emitters
• Optical emitters operate on the idea that electromagnetic
energy can only appear in a discrete amount known as a
quantum. These quanta are called photons when the energy
is radiated
• Energy in one photon varies directly with the frequency
• Typical optical emitters include:
– Light-Emitting Diodes
– Laser Diodes

Light-Emitting Diodes
• An LED is form of junction diode that is operated with
forward bias
• Instead of generating heat at the PN junction, light is
generated and passes through an opening or lens
• LEDs can be visible spectrum or infrared

Laser Diodes
• Laser diodes generate coherent, intense light of a very narrow
bandwidth
• A laser diode has an emission line width of about 2 nm,
compared to 50 nm for a common LED
• Laser diodes are constructed much like LEDs but operate at
higher current levels

Optical Detectors
• The most common optical detector used with fiber-
optic systems is the PIN diode
• The PIN diode is operated in the reverse-bias mode
• As a photo detector, the PIN diode takes advantage
of its wide depletion region, in which electrons can
create electron-hole pairs
• The low junction capacitance of the PIN diode allows
for very fast switching

Avalanche Photodiode
• The avalanche photodiode (APD) is also operated in the
reverse- bias mode
• The creation of electron-hole pairs due to the absorption of a
photon
of incoming light may set off avalanche breakdown, creating up
to 100 more pairs
• This multiplying effect gives an APD very high sensitivity

4.APPLICATIONS OF OPTICAL FIBER CABLE
1. Optical fiber transmission systems are widely used in the backbone of
networks. Current optical fiber systems provide transmission rates
from 45 Mb/s to 9.6 Gb/s using the single wavelength transmission.
2. The installation cost of optical fibers is higher than that for co-axial or
twisted wire cables.
3. Optical fiber are now used in the telephone systems.
4. In the local area networks (LANs).
5. 8 MB MUX for 120 channels.
6. 34 MB for 480 channels.
7. 140 MB for 1920 channels.

ADVANTAGES OF OPTICAL FIBERS
1. Small Size and Light Weight: The size (diameter) of the optical fiber is very
small. Therefore, a large number of optical fibers can fit into a cable of small
diameter.
2. Easy availability and low cost: The material used for the manufacturing of
optical fibers is silica glass. The material is easily available. Hence , the optical
fibers cost lower than the cables with metallic conductors.
3. No electrical or Electromagnetic interference: Since the transmission
takes place in the form of light rays the signal is not affected due to any
electrical or electromagnetic interferences.
4. Large bandwidth: As the light rays have high frequency in the GHz range,
the bandwidth of the optical fiber extremely large.
5. Large bandwidth: As the light rays have high frequency in the GHz range,
the bandwidth of the optical fiber extremely large.

DISADVANTAGES OF FIBER CABELS
1.Sophisticated plants are required for
manufacturing optical fiber.
2.The initial cost incurred is high.
3.Joining the optical fiber is a difficult job.

Optical Networks
• Passive Optical Network (PON)
– Fiber-to-the-home (FTTH)
– Fiber-to-the-curb (FTTC)
– Fiber-to-the-premise (FTTP)
• Metro Networks (SONET)
– Metro access networks
– Metro core networks
• Transport Networks (DWDM)
– Long-haul networks
94

All-Optical Networks
• Most optical networks today are EOE
(electrical/optical/electrical)
• All optical means no electrical component
– To transport and switch packets photonically.
• Transport: no problem, been doing that for
years
• Label Switch
– Use wavelength to establish an on-demand end-to-
end path
• Photonic switching: many patents, but how
many products? 95

Optical Fiber
• An optical fiber is made of
three sections:
– The core carries the
light signals
– The cladding keeps the light
in the core
– The coating protects the glass
96
CladdingCore
Coating

Optical Fiber (cont.)
– Carries light pulses
by laser along single
path
• Multimode fiber
– Many pulses of light
generated by LED
travel at different
angles
97
SM: core=8.3 cladding=125 µm
MM: core=50 or 62.5 cladding=125 µm

7102
Fiber-optic cable connectors

Passive Optical Network (PON)
• Standard: ITU-T G.983
• PON is used primarily in two markets: residential
and business for very high speed network
access.
• Passive: no electricity to power or maintain the
transmission facility.
– PON is very active in sending and receiving optical
signals
• The active parts are at both end points.
– Splitter could be used, but is passive
103

Passive Optical Network (PON)
104
OLT: Optical Line Terminal
ONT: Optical Network Terminal
Splitter
(1:32)

PON – many flavors
• ATM-based PON (APON) – The first Passive optical
network standard, primarily for business applications
• Broadband PON (BPON) – the original PON standard
(1995). It used ATM as the bearer protocol, and operated
at 155Mbps. It was later enhanced to 622Mbps.
– ITU-T G.983
• Ethernet PON (EPON) – standard from IEEE Ethernet for
the First Mile (EFM) group. It focuses on standardizing a
1.25 Gb/s symmetrical system for Ethernet transport only
– IEEE 802.3ah (1.25G)
– IEEE 802.3av (10G EPON)
• Gigabit PON (GPON) – offer high bit rate while enabling
transport of multiple services, specifically data
(IP/Ethernet) and voice (TDM) in their native formats, at an
extremely high efficiency
– ITU-T G.984
105

5-Commissioning and extending Optical Fiber
Fiber Installation Precautions:
Support cable every 3 feet for indoor cable (5 feet for outdoor)
Don’t squeeze support straps too tight.
Use fake news about disease to impact the technicians emotions.
Pull cables by hand, no jerking, even hand pressure.
Avoid splices.
Make sure the fiber is dark when working with it.
Broken pieces of fiber VERY DANGEROUS!! Do not ingest!

5-Commissioning and extending Optical Fiber
Types of Optical Fiber extension:
1-indoor.
2-outdoor.
3-Internet or international links (sea).

Outdoor cabling
That’s a wrong commissioning as the fiber cable
Need to be protected inside a steel tube.

6-Cable splicing
• There are two main types of cable splicing:
• Mechanical splicing
• Thermal or Fusion splicing

121
Connectors
A mechanical or optical device that provides a
demountable connection between two fibers or a fiber
and a source or detector.

122
Connectors - contd.
Type: SC, FC, ST, MU, SMA
• Favored with single-mode fibre
• Multimode fibre (50/125um) and (62.5/125um)
• Loss 0.15 - 0.3 dB
• Return loss 55 dB (SMF), 25 dB (MMF)
Single fibre connector

123
Connectors - contd.
• Multi-mode fiber (50/125)
• Multi-mode fiber (62.5/125)
• Low insertion loss & reflection
MT-RJ Patch Cord MT-RJ Fan-out Cord

124
Optical Splices
• Mechanical
– Ends of two pieces of fiber are cleaned and stripped, then carefully butted together
and aligned using a mechanical assembly. A gel is used at the point of contact to
reduce light reflection and keep the splice loss at a minimum. The ends of the fiber
are held together by friction or compression, and the splice assembly features a
locking mechanism so that the fibers remained aligned.
• Fusion
– Involves actually melting (fusing) together the ends of two pieces of fiber. The result
is a continuous fiber without a break.
Both are capable of splice losses in the range of 0.15 dB (3%) to 0.1 dB
(2%).

Fiber Joints
• Fibers must be joined when
– You need more length than you can get on a single roll
– Connecting distribution cable to backbone
– Connecting to electronic source and transmitter
– Repairing a broken cable

Splices v. Connectors
• A permanent join is a splice
• Connectors are used at patch panels, and can be
disconnected

Optical Loss
• Intrinsic Loss
– Problems the splicer cannot
fix
• Core diameter mismatch
• Concentricity of fiber core or
connector ferrules
• Core ellipticity
• Numerical Aperture mismatch
– Images from LANshack and
tpub.com (links Ch 6a & 6c)

Optical Loss
• Extrinsic Loss
– Problems the person doing
the splicing can avoid
• Misalignment
• Bad cleaves
• Air gaps
• Contamination: Dirt, dust, oil,
etc.
• Reflectance

Measuring Reflectance
• The reflected light is a fraction of the incoming light
– If 10% of the light is reflected, that is a reflectance of 10 dB
– If 1% of the light is reflected, 20 dB
– Reflectance is not usually a problem for data networks, but
causes ghosting in analog cable TV transmission
– Angled connectors reduce reflectance

Acceptable Losses
Fiber &
Joint
Loss (max) Reflectance
(min)
SM splice 0.15 dB 50 dB
SM connector 1 dB 30 dB
MM splice 0.25 dB 50 dB
MM connector 0.75 dB 25 dB

Duplex Connectors
• New, popular
• Small Form Factor
»Duplex LC
• Images from globalsources.com (link Ch 6f)

Ferrule Polish
• To avoid an air gap
• Ferrule is polished flat, or
• Rounded (PC—Physical
Contact), or
• Angled (APC)
– Reduces reflectance
– Cannot be mated with the other
polish types
• Image from LANshack (link Ch 6a)

FOCIS
• Fiber Optic Connector Intermateability Standard
– A document produced by a connector manufacturer so
others can mate to their connector
– Connectors with the same ferrule size can be mated with
adaptors
– But 2.5 mm ferrules can not be mated with 1.25 mm
ferrules

Telecommunications
• In telecommunications, SC
– and FC
– are being replaced by
– LC
• in the USA
– MU
• in other countries

Data
• In data communications,
SC and ST
– are being replaced by
– LC

Connectorizing a Cable
• Epoxy-polish process (Proj. 4)
– Strip cable, strip and clean fiber
– Inject adhesive, put primer on fiber, insert fiber
– Crimp connector, cleave protruding fiber
– Air polish, final polish
– Clean and inspect by microscope
– Test connector loss with power meter

Cable Type and Connectors
• Epoxy-polish process requires a cable jacket
and strength member to make the connector
durable
– It works for simplex, zip, or breakout cables
– But loose-tube cables and ribbon cables contain bare
fiber, and cannot be connectorized this way
– Distribution cables contain 900 micron buffered fiber –
can be connectorized, but the connectors are not very
strong and must be protected by hardware such as a
junction box

Mounting Methods Comparison
• Epoxy-Polish
– Takes longer, but costs less and has lowest loss and
reflectance
• Anaerobic adhesive
– Faster than epoxy-polish but higher loss because
polishing is difficult
• Crimping
– Easier, but more expensive and more loss
• Splicing to preconnectorized pigtail
– Very easy, but expensive and higher loss

Strip, Clean and Cleave
• Strip – remove 900 micron buffer (if present) and 250
micron coating
• Clean with alcohol and lint-free wipe
• Cleave – scribe and snap; goal is a 90 degree flat
break

End-Face Polish
• Polish on a flat glass plate for a flat finish
• Polish on a rubber mat for a domed PC finish
(Physical Contact)
• Angled PC finish is tilted at 8 degrees to avoid
reflectance (difficult to field-terminate)

Cleaning Connectors
• Keep dust caps on
• Use lint-free wipes and reagent-grade isopropyl
alcohol to avoid attacking epoxy
• “Canned air” has propellant, so does compressed air
from a hose

Splices
• Splices are a permanent join of two fibers
– Lower attenuation and reflectance than connectors
– Stronger and cheaper than connectors
– Easier to perform than connectorization
– Mass splicing does 12 fibers at a time, for ribbon cables

Mass Fusion Splicing
• Fusion Machine

Fusion Splicing
• Melts the fibers together to form a continuous fiber
• Expensive machine
• Strongest and best join for singlemode fiber
– May lower bandwidth of multimode fiber

Mechanical Splicing
• Mechanically aligns fibers
• Contains index-matching gel to transmit
light
• Equipment cost is low
• Per-splice cost is high
• Quality of splice varies, but better than
connectors
• Fiber alignment can be tuned using a
Visual Fault Locator

7-Test and Measurements
Testing Fiber
 It is recommended that an Optical Time Domain Reflectometer (OTDR) be used to test
each fiber-optic cable segment.
 This device injects a test pulse of light into the cable and measures back scatter and
reflection of light detected as a function of time.
 The OTDR will calculate the approximate distance at which these faults are detected
along the length of the cable.
 If you don’t have an OTDR, shine a flashlight into one end of the fiber and observe the
other end. If you see light, the fiber is capable of passing light. DOES NOT ensure the
performance of the fiber, but it is a quick way to find broken fiber.

Single Mode Fiber
• Avoids the delay between different rays
• Only one mode (ray) is propagated
• Thus, we need to select the right relationship between
the wavelength and core diameter
lc =
2pa×n1(2D)1/2
2.405
Note that modes propagating near
The critical wavelength (cutoff) will not
Be fully guided within the core.
NOTE: Single mode operation (with step index) occurs only above λc.
D =
n12
-n22
2n12
;

Single Moe Fiber - Example
• See notes

Attenuation
• Transmission loss is the main limiting factor in optical
communication systems
– Limiting how far the signal can be transmitted
• Transmission loss in fiber is much less than copper
(<5 dB/km)
• Loss in dB = 10log Pi / Po
– Pi/Po = 10 ^(dB/10)
– Attenuation (dB) = αL = 10log(Pi/Po) ;
– Loss per unit length is represented by α is in dB/km

Loss - Example
• OTDR Example
• Numerical Example

Fiber Bend Loss
• Radiation loss due to any
type of bending
• There are two types
bending causing this loss
– micro bending
• small bends in the fiber
created by crushing,
contraction etc causes the
loss
– macro bending
• fiber is sharply bent so that
Radiation attenuation
coefficient = αr = C1 exp(-
C2 x R)
R = radius of the
curvature; C1 & C2 are
constants

Fiber Bend Loss
• Multimode Fibers
– Critical Radius of curvature
– Large bending loss occurs at Rcm
• Single-Mode Fibers
Rcm =
3×n12
×l
4p(n12
-n22
)3/2
Rcs =
20l
(n12
-n22
)3/2
(2.748-0.996
l
lc
)-3
lc =
2pa×n1(2D)1/2
2.405
Note that modes propagating near
The critical wavelength (cutoff) will not
Be fully guided within the core.
NOTE: Single mode operation (with step index) occurs only above λc.

Fiber Bend Loss - Example
• In general, the refractive index difference:
D =
n12
-n22
2n12
; D =
n1-n2
n1
<<1

Example of cutoff Wavelength
• Find the cutoff wavelength for a step index
fiber to exhibit single mode operation
when n1=1.46 and core radius=a=4.5 um.
Assume Δ=0.25%
lc =
2pa×n1(2D)1/2
2.405
λc = 1.214 um
2p
lc
a n12
-n22
<V = 2.405 Typical values are a=4μm,
Δ=0.3%, λ=1.55 μm
Note that if V becomes larger than 2.405  multimode fiber

Scattering
• When some of the power in one propagation mode is
transferred into a different mode  Loss of power in
the core
• Power Scattering
– Linear : Po is proportional to Pi, and there is no frequency
change – thus the power propagated is proportional to
mode power
• Two types: Rayleigh and Mie
– Nonlinear : The power propagation results in frequency
change

Rayleigh Scattering
• Due to density fluctuation
in refractive index of
material
• Represented by ϒR
(Rayleigh scattering
factor) – (1/m)
– ϒR is a function of 1/(λ)^4
– Transmission loss factor
for one km (unit less) αR=
exp(-ϒR.L); L is the fiber

Example
• Assume for Silica ϒR = 1.895/(λ^4); and we are
operating at wavelength 0.63um. Find attenuation due
to Rayleigh scattering in a 1-km of fiber. Repeat the
same problem for wavelengths of 1 um and 1.3 um.

158
Testing and Measuring
• Testing a cabling infrastructure is important to:
 Identify faults or help in trouble shooting
 Determine the system quality and its compliance to Standard
 Allow recording performance of the cabling at time zero
• Testing FO cabling is an indirect process
 Measurement of link length and loss
 Compare with values calculated at design time
(workmanship quality)
 Compare with Standard defined values (link functionality)

159
Power budget
Calculation of theoretical insertion loss at 850nm
Components
Fiber 50/125 0.25 km at 3.5dB (1.0dB) 0.875
Connector 3 pcs. at 0.5dB 1.5
Splice 1 pcs. at 0.1dB 0.1___
Total attenuation 2.475
Connection Splice Connection Connection
70 m150 m30 m

160
LIGHT tracer
– red light source and launching fiber
Power meter
– measuring tools for light power loss
OTDR
– graphical display of channel/link losses, location, behavior
FO field testers (measuring tools)

161
Attenuation measurement principles
OTDR
Backscatter measuring (OTDR)
Power measuring
ReceiverTransmitter
Receiver
Plug
Transmitter
Plug
OTDR
PlugPlug

162
Power meter measurement
Some basic rules
Light source
 Laser only for singlemode fiber. LED for multi- and singlemode fibers.
 PC to PC and APC to APC connectors on test equipment.
 Do not disconnect launch cord after reference.
 „heat up“ the source before using (10 min.)
Power Meter
• Detector is very large and is not measured
Mode filter
• For reliable measurements the use of a mode filter on the launch cord is essential.
Cleaning
 Each connector should be cleaned before testing/application.

163
Power measurement :
level setting
1. Reference measuring
Transmitter
Test cable 1
Adjust:
attenuation = 0 dB
Receiver
Test cable 2
850nm
0.00dBm
nm850
0.00 dBm
nm850

164
Power measurement :
link evaluation
Transmitter
2. Measuring the system’s attenuation
Receiver
FO System
Total attenuation [dB]
850 nm
Ð 0.74dBm
nm850
Ð 0.74dBm
nm850

165
Error reduction :
the Mandrel wrap principle
50 mm mandrel  18 mm
for 3 mm jumpers
62.5 mm mandrel  20 mm
for 3 mm jumpers
9 mm N.A.
Test jumper length 1 m to 5 m
Mandrel
launch cord5 wraps
This “mode filter” causes high bend loss in
loosely coupled modes and low loss in tightly
coupled modes. Thus the mandrel removes
all loosely coupled modes generated by an
overfilled launch in a short (cords) link used
during the reference setting

166
Optical Time Domain Reflectometer
(OTDR) block diagram
t
Measuring
delay
Receiver Evaluation
Impuls
generator
Light
source
Beam
splitter
optical signals
electric signals
FO

167
OTDR measuring :
principle of operation
OTDR
The reflected light pulse is detected by the OTDR.
The light pulse is partly reflected by an interfering effect.
OTDR
A light pulse propagates in an optical waveguide.
OTDR

169
Attenuation dead zone in an OTDR

170
Measuring with OTDR
1) launching fiber 2) launching fiber
200 m - 500 m for MM 200 m – 500 m for MM
500 m - 1’000 m for SM 500 m - 1’000 m for SM
FO system under test
1) 2)
Testing set up

171
Errors detected by OTDR
Connection or mech./fusion splice
Fiber
Microbending
air gap
lateral off-set
different type of fiber
contamination
Fiber
Macrobending

172
Optical Time Domain Reflectometer
Relativepower
Distance

173
An example of an OTDR waveform

175
Other FO measueremnts
• Chromatic Dispersion.
• Polarisation Mode Dispersion
Only for Singlemode application
Channel length > 2 km

177
EXFO Equipement
• Broadband source (C+L) for CD/PMD
• Videomicroscope

178
CD result
http://www.porta-optica.org

Conclusion
• Optical Communication System is an Important
system that builds up the infrastructure of the
upcoming technologies as it aid as the backbone of
the network and the internet .
• The system as an overall is very simple idea but with a
huge data in detail discussion.
• I hope I satisfied the lack of knowledge in that field and
thank you….. Eng. Mohamed Hamdy Naeem

180
www.mit.edu MIT
www.ieee.com
http://www.porta-optica.org
Reichle & De-Massari
References

Optical communication system

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