Transcript Wavelength Division Multiplexing

Optical Communication
Systems
NITIN KUMAR
Asst Professor
Electronics & comm. Engineering Deptt
SDEC, GHAZIABAD
OVERVIEW
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Information Systems Evolution & What is it ?
Why there is Demand of Large bandwidth ?
Why Optical Fiber Technology ?
Optical Transmission fundamentals.
How to Explode the optical fiber bandwidth ?
Data rate requirements for high speed
networks.
Optical Fiber Solutions for today’s Systems &
Networks.
An Information Model
Definition:
Delivering information to an
authorized user when it is
needed, wherever it is needed i.e,
regardless of the physical
location of the user or of the
information, and whatever form
it is needed in a secure way.
Information Systems
Evolution
Compared to legacy systems today’s Systems
are:
- Data oriented, large, and complex
- On-line, interactive with strong emphasis on
user interface e.g. Graphical User Interface
- Global, distributed and extensive in their
reach
- More volatile and subjective to constant
change
 Today’s systems often require reuse of
components of existing systems and building
new systems to deal with changes
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Needs For Today’s Optical Systems
 Increase capacity of transmission
(bit/sec).
 Minimize insertion loss (dB).
 Minimize polarization dependent loss
(PDL).
 Minimize temperature dependence of
the optical performance (a thermal
solutions).
 Minimize component packaging size
(integrability).
 Modularity of components is an
advantage (versatility)
Trends
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Internet: A Deriving force
SOME ACTUAL FACTS
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12 Million email messages in next minute
0.5 Million voice mail messages in next minute
3.7 Million people log on the net today
Next 100 days, Internet traffic doubles
100 Million additional internet users every year
Data based on the survey at Bell Laboratories, USA in Nov., 2000.
DEMAND FOR MORE BANDWIDTH
ONLY SOLUTION IS
OPTICAL COMMUNICATION
The Race for Bandwidth
1995
2001
World Wide
Web Users
World Wide
Web Servers
Monthly
Internet
Traffic
Internet
Backbone
Demand
6 Million
300+
Million
100K
17+
Million
31 Terabytes 350,000
Terabytes
Doubles
Every 6
Months
Exploding Demands for
Bandwidth
Optical Fiber Bandwidth as a function of time
40 X OC– 92 denotes 40 wavelength channels
OC-48= 2.5Gb/s, OC-192=10Gb/s, OC-768=40Gb/s
Trunk transmission capacity
# WDM-channels
256
‘99
•
•
‘97
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64
‘98
16
•
‘02?
•
‘96
4
‘80 ‘83
1
0.01
‘00
• 0.1•
‘86
•
1
•
‘89
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Channel bitrate (Gb/s)
‘98
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10
100
Do We Need Terabits ?
Information Systems
 Computing Shift
 The Internet
 Ligthwave Capacity
Trends
 Global Networking
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Facts Regarding Optical
Transmission
BIT RATE INCREASING
TRANSMISSION DISTANCE INCREASING
Capacity Growth of Optical Fiber
Each Year
Year
Capacity (Gb/s)
 1980
0.1
 1985
1
 1990
3
 1995
5
 2000
100 (40 practically shown)
 2005
1,000 (If
limitations due to Dispersion &
Nonlinearities are overcome)
The optical world is approaching
towards
1. 50 THz Transmission Window
 1000 Channel WDM
 100 Gb/s TDM
 1000 km Repeater less transmission
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If Nonlinearities can be
controlled, transmission window
will be 300THz
Optical Fiber Applications
Fiber to the Home
OFC Backbone Capacity
Bandwidth-What is it ?
Bandwidth is the a measure of information
carrying capacity of a medium.
 To the digital word, it is translated into a
maximum bit rate at which signals can be sent
without significant signal degradation
 Fiber bandwidth is typically quoted in frequency
and normalized to fiber length (MHz-Km)
- As length increases bandwidth decreases
 A fiber bandwidth is determined by its pulse
spreading properties
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Bandwidth-What is it ?
The difference between the highest
and lowest frequencies of a band that
can be passed by a transmission
medium without undue distortion.
 A term used to indicate the amount of
transmission or processing capacity
possessed by a system or specific
location in a system (Usually a network
system)
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Copper Versus Fiber: Repeaters
Eliminate the dangers found in areas of
high lightning-strike
Fiber links offer over 1,000 times as
much bandwidth and distances over
100 times
Distance Bandwid
Voice
th
Channels
Copper
2.5 km
1.5 Mb/s
24
Fiber
200 KM
2.5+
Gb/s
32,000 +
Electromagnetic Spectrum
Introduction to Optical
COmmunication
 The
first practical scheme of optical
communication, was invented by Alexander
Grahm Bell, in 1880, the Photophone.
 Photophone: Device in which speech can be
transmitted on a beam of light, using mirrors &
selenium detectors.
 Present optical communication systems use Laser
& Optical Fiber technologies.
 Optical frequency is typically 1014 Hz, which can
support wideband modulation. Compared to
microwave frequencies 109 Hz, the optical career
can offer 105 times more bandwidth.
Basics of Fiber Optic Communication
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Fiber Optics is a revolutionary development
that has changed the face of
telecommunications around the world
Transmission of data as a light pulses
through optical fiber (first converting
electronic binary signals to light and then
finally converting back to electronic
signals)
Elements of Fiber Optics
 Transmission
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Light Source (such as Infrared LED converts
pulses and sends into optical fiber)
850 nm, 1300 nm
 Low cost, easy to use
 Used for multi mode fiber
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Basics of Fiber Optic Communication
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(Contd..)
Laser Source having properties
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Coherence
Monochromaticity
Directionality
High Specific Intensity
850 nm, 1300 nm, 1550 nm
Very high power output
Very high speed operation
Very expensive
Need specialized power supply & circuitry
Reception
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Photo detector converts back to electrical pulses
PIN DIODES
 850, 1300, 1550 nm
 Low cost
 APDs (Avalanche Photodiodes)
 850, 1300, 1500 nm
 High sensitivity, can operate at very low power levels
 expensive
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Basics of Fiber Optic Communication
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(Contd..)
Propagation in Fiber
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Light propagates by mans of total internal reflection.
Optical Fiber consists of two concentric layers
Core – inner layer
 Cladding – outer layer
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Refractive index of core is greater than cladding,
necessary for total internal reflection
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Light entering with acceptance angle propagates through
fiber
Strikes core cladding interface > critical angle and gets
reflected completely.
 Zig-zags down length of core through repeated reflections.
 Fairly lossless propagation through bends also.
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Optical fiber
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Multimode (Graded Index 50/125 & 62.5/125  )
Single mode (8.7 /125  )
Basics of Fiber Optic Communication
 Major
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(Contd..)
Advantages of FOC
Large Bandwidth (Extremely high information carrying
capacity)
Carrier frequency – Light – 1014 Hz
 Makes possible widespread long distance communication of
high bandwidth signals
 Color video
 High speed network
 High degree of Multiplexing, without much interference among
them.
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Low Loss (Long repeaterless link length/repeater spacing)
Loss as low as 0.1 dB/Km
 Repeater spacing of over 100 Km possible over land & under
sea.
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EMI immunity (Even in noisy or harsh environmentsLightning, factory floor, high voltage lines, broadcast
towers)
Basics of Fiber Optic Communication
 Major
(Contd..)
Advantages of FOC (Contd..)
 Compact and light weight
 Single fiber can easily replace 1000 pair copper cable of
10 cm dia.
 Security
(impossible to tap)
 Safety (insulator & no sparks – ideal for hazardous
environment)
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Can be used in
 Oil exploration
 Oil refineries
 Mines
 Explosives
 Petrochemical
 Other hazardous chemical
Basics of Fiber Optic Communication
 Some
(Contd..)
practical disadvantages of FOC
 Fiber
is expensive
 Connectors very expensive (due to degree of
precision involved)
 Connector installation time consuming & highly
skilled operation
 Joining (splicing) of fibers requires expensive
equipment & skilled operators
 Connections & joints are relatively lossy
 Difficult to tap in & out (for bus architectures)
need expensive couplers
 Relatively careful handling required
Advances in Optical Communication
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First Generation Support:
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Second Generation Support:
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Operating at: 850 nm
Bit Rates: 50 -100 Mbps
Repeater Spans: 10 Kms
Sources & Detectors made of InGaAsP compound
semiconductor
Operating at: 1300 nm
Bit Rates: 1-2 Gbps
Repeater Spans: 40 -50 Kms
Sources & Detectors made of InGaAsP compound
semiconductor
Third Generation Support:
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Operating at: 1550 nm
Bit Rates: 2.4 Gbps
Repeater Spans: 100 Kms
Advances in Optical Communication (Contd..)
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Present Standards Supported:
Various
multiplexing techniques for enhanced capacity
utilization, use of optical amplifiers & Soliton – based
transmission systems developed.
Speed & Repeater spacing due to fiber optic systems, newer
standards such as:
•FDDI (Fiber Distributed Data Interface)
•DQDB (Dual Queue Distributed Bus)
•SONET (Synchronous Optical Network)
•SDH (Synchronous Digital Hierarchy)
Advances in Optical Communication (Contd..)
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More Advanced Systems:
Era
of high capacity Trans Atlantic Telecommunication (TAT)
began as under:
TAT
- 2 in 1959
TAT – 6 in 1976
TAT – 7 in 1983 (offered a capacity of about 4000 analog
circuits)
Optical fiber based TAT – 8 in 1989 (offered 40,000 circuits,
64,000 Km long, 280 Mbps, 40 Km repeater distance )
TAT - 12/13 with many new features is now operational
Some other fiber systems include HAW – 4 (Hawaiian Cable
4), TPC – 3(Trans – Pacific Cable –3)
Advances in Optical Communication (Contd..)
Further
achievements include
Fiber losses 0.16 dB/Km (at 1550 nm)
Laser with threshold currents of few milli-amperes and
life time of over a million hours
Repeater spans of more than 200 Kms.
Transmission rates in excess of 2 Gbps
Advent of EDOFA (Erbium-Doped optical fiber amplifier),
using dispersion compensating Soliton transmission
techniques or the use of dispersion compensating fibers
(DCF) and the improvements made in the attenuation &
dispersion characteristics of the modern optical fiber have
led to the demonstration of data transmission in
experiments with repeaterless spans of over 10,000 Km
and bit rates in excess of 10 Gbps
More complex coherent optical communication,
wavelength routed, dense wavelength division
multiplexing (DWDM) links are available.
Advances in Optical Communication (Contd..)
Coherent communication systems make use of:
Sources & detectors made of quantum well
structures with high directional properties.
Single mode single polarization optical fiber having
very low loss and very low dispersion.
Has superior SNR capabilities, long repeater spans
& high bit rates.
WDM (Wavelength Division Multiplexing)
Provides an easy way to increase the utilization of
the high channel channel capacity of the optical fiber.
Integrated Optics
Deals with the miniaturization & integration on a
single substrate optical components such as
- electro optic modulator
- polarization controller
- splitters / combiners
- directional couplers
- lenses
Advances in Optical Communication (Contd..)
-Optical MEMs make use of silicon micro machining to
realize micro-opto-mechanical elements
-Soliton Propagation in Optical Fibers
-Initially launched pulse may propagate with ultra-low
dispersion over thousands of Kilometers
-Active devices within fibers EDFA (Erbium Doped
Fiber Amplifiers) are now available.
-Photonic switching architectures (which use
integrated optic switches) & optical MEMs provides
data – rate transparent switching services to optical
fiber based trunks
Advances in Optical Communication (Contd..)
Features of Present Optical
Communication
S ig n a l s
S y ste m s
S ta n d a r d s
D e p lo y m e n t
P h o t o n ic
T ec h n o lo g y
V o i c e , D a ta , V i d e o , I n t e g r a t e d S e r v ic e s
P o i n t - to - P o i n t, M u lt ip o i n t, S h o r t - h a u l,
L o n g -H a u l ( U n d e r s e a )
S O N E T /S D H , F D D I , I S D N , B I S D N , A T M
LAN , M AN , W AN , C ATV , H FC, FTTC,
FTTH
P h o t o n ic s w it c h i n g , W D M /T D M /O F D M ,
A l l o p t i c a l/p h o t o n ic n e t w o r k s , S o li to n
S y s t e m s , O p ti c a l a m p li fi c a ti o n
Advances in Optical Communication (Contd..)
System Design Issues
Source
LED
Diode
Quantum
Noise
Noise
Bandwidth
Limit
noise
Laser
Quantum
Mode
Partition
Bandwidth
Limit
Receiver
Detector
Fiber
Amplifier
Quantum Noise Optical:
Spontaneous
emission noise
Mode partition
noise
Shot noise
Shot
Electronic:
Dispersion limit
& thermal
Non-linear effects
noise
Bandwidth
Limit
Bandwidth
Limit
Information Transmission
Sequence
Optical Communication Systems
First Generation, ~1975, 0.8 m
MM-fibre, GaAs-laser or LED
Second Generation, ~1980, 1.3 m, MM & SM-fibre
InGaAsP FP-laser or LED
Third Generation, ~1985, 1.55 m, SM-fibre
InGaAsP DFB-laser, ~ 1990 Optical amplifiers
Fourth Generation, 1996, 1.55 m
WDM-systems
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Wavelength (m)
Fiber Structure
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A Core Carries most of the light, surrounded by
A Cladding, Which bends the light and confines it
to the core, covered by
A primary buffer coating which provides
mechanical protection, covered by
A secondary buffer coating, which protects
primary coating and the underlying fiber.
Fiber Structure Cont…
Types Of Optical Fibre
Light
ray
Single-mode step-index fibre
Multimode step-index fibre
n1 core
n2 cladding
no air
n1 core
n2 cladding
no air
Variable
n
Multimode graded-index fibre
Index porfile
Multimode Step Index Fiber
Core diameter range from 50-1000m
 Light propagate in many different ray
paths, or modes, hence the name
multimode
 Index of refraction is same all across the
core of the fiber
 Bandwidth range 20-30 MHz
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Multimode Graded Index Fiber
The index of refraction across the core
is gradually changed from a maximum
at the center to a minimum near the
edges, hence the name “Graded Index”
 Bandwidth ranges from 100MHz-Km to
1GHz-Km
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Pulse Spreading
T
Pulse from zero-order mode
T
T
Pulses from other modes
T
Pulse from highest-order mode
T
Resulting pulse
time
Calculation of Pulse Spread
y/2
y/2


C
C
x
x  y cosC
Modes of Vibration of a String
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Lowest order mode
A1 sin(0t )
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Second order mode
A2 sin(20t )

Third order mode
A3 sin(30t )
Single-Mode Graded Index Fiber
The Core diameter is 8 to 9m
 All the multiple-mode or multimode
effects are eliminated
 However, pulse spreading remains
 Bandwidth range 100GHz-Km
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Typical Core and Cladding
Diameters (m)
Acceptance Cone & Numerical
Aperture
Acceptance
Cone
n2 cladding
n1 core
qC
n2 cladding
Acceptance angle, qc, is the maximum angle in which
external light rays may strike the air/fibre interface
and still propagate down the fibre with <10 dB loss.
q C  sin
1
n1  n2
2
2
Numerical aperture:
NA = sin qc = (n12 - n22)
Multiple OFC
Standard Optical Core Size
•The standard telecommunications core sizes in
use today are:
8.3 µm (single-mode),
50-62.5 µm (multimode)
Thanks