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Dense Width DivisionMultiplexing

Dense Wavelength Division
Multiplexing (DWDM)
DWDM Technology
DWDM System & Components
Transmission Challenges
Market Dynamics
Evolution of Fiber Optic
In mid 1960’s researchers proposed optical fiber
as suitable transmission medium.
In 1970 , Corning produced the first communication –grade fibers.
AT& T first standardized transmission at DS3
speed(45Mbps) for multimode fibers.
Thereafter, single mode fibers were shown to be
capable of transmission rates 10 times
that of older type.
In early 1980’s,MCI, followed by Sprint, adopted
single mode fiber for its long distance network in
Further developments in fiber optics was tied to use
of the specific regions on the optical spectrum
where attenuation is low.
These regions called windows, lie between
area of high absorption.
Wavelength Regions
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
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 .
Unlimited Transmission Capacity
Dynamic Provisioning
Is DWDM Flexible?
DWDM is a protocol and bit rate independent
hence, data signals such as ATM, SONET and IP
can be transmitted through same stream
regardless their speed difference.
The signals are never terminated within the
optical layer allows the independence of bit rate
and protocols,allowing DWDM technology to be
integrated with existing equipment in network.
Hence, there’s a flexibility to expand capacity
within any portion of their networks.
Is DWDM Expandable?
“ DWDM technology gives us the ability to
expand out fiber network rapidly to meet growing
demands of our customer”, said Mike Flynn,
group President for ALLTEL’s communications
DWDM coupled with ATM simplifies the
network, reduce network costs and provide new
They can add current and new TDM systems to
their existing technology to create a system with
virtually endless capacity expansion
Structure of DWDM Link
DWDM System
Block Diagram of DWDM System
Optical Transmission Principles:
Channel Spacing
Signal Direction: Uni and Bi-directional
Signal Trace
Network Classification
Ring topology vs. Mesh topology
Single hop vs. Multi-hop Networks
Optical Amplifiers
DWDM Components
Transmitter : Laser with precise stable wavelength.
Link: Optical fiber that exhibits low loss and
transmission performance in relevant wavelength
Receiver:Photo detectors and Optical demultiplexers using thin film filters or diffractive elements.
Optical add/drop multiplexers and optical cross
connect components.
DWDM Point to Point
DWDM Mesh Designs
Advantages of DWDM Point to
Point Systems
The DWDM point-to-point architecture is simple
to build and troubleshoot .
It enables protocol transparency, increme-ntal
growth, and capacity expansion over time, while
dramatically reducing start-up costs.
Point-to-point solutions are also extremely
No amplifiers or additional equipment required.
DWDM System Characteristics
component reliability, system availability, and
system margin. Although filters were often
susceptible to humidity, this is no longer the case.
An optical amplifier has two key elements: the
optical fiber that is doped with the element
erbium and the amplifier.
Automatic adjustment of the optical amplifiers
when channels are added or removed achieves
optimal system performance.
In the 1530- to 1565-nm range, silica-based
optical amplifiers with filters and fluoride-based
optical amplifiers perform equally well.
The system wavelength and bit rate can be
upgraded but planning for this is critical.
Transmission Challenges
 Attenuation is caused by :
- intrinsic factors primarily scattering and
- extrinsic factors, including stress from the
manufacturing process, the environment, and
physical bending
 Rayleigh scattering - is an issue at shorter
Rayleigh Scattering
Attenuation due to absorption
- is an issue at longer wavelengths
- the intrinsic properties of the material
- impurities in the glass, and any atomic defects
in the glass.
These impurities absorb the optical energy,
causing the light to become dimmer.
 Dispersion is the spreading of light pulses as they
travel down optical fiber. Dispersion results in
distortion of the signal, which limits the
bandwidth of the fiber.
Two general types of dispersion
Chromatic Dispersion - is linear
 Chromatic dispersion occurs because different
wavelengths propagate at different speeds.
 Increases as the square of the bit rate.
Polarization Mode Dispersion - is nonlinear.
 Polarization mode dispersion (PMD) is caused by
ovality of the fiber shape as a result of the
manufacturing process or from external stressors.
Changes over time
PMD is generally not a problem at speeds below
 Smearing of the signal
Fiber Non Linear ties
 Because nonlinear effects tend to manifest
themselves when optical power is very high, they
become important in DWDM.
These nonlinearities fall into two broad groups:
- scattering phenomena
- refractive index phenomena
Scattering Phenomena
- Stimulated Brillouin Scattering (SBS)
- Stimulated Raman Scattering (SRS)
 use moderate channel powers and densely packed
channel plan that minimizes the overall width of
the spectrum.
Refractive Index Phenomena
 This group of nonlinearities includes
- self-phase modulation (SPM)
- cross-phase modulation (CPM)
- four-wave mixing (FWM)
- This phenomena causes the signal's
spectrum to widen and can lead to crosstalk or
an unexpected dispersion penalty.
Four-wave mixing
- results in cross-talk and signal-to-noise
- troublesome in the dispersion shifted fiber
that is used to propagate STM-64/OC-192.
- limit the channel capacity of a DWDM
Market Scope and Company
KMI Corporation
The DWDM systems market jumped from $4.2
billion in 1999 to $8.9 billion in 2000.
From $1.7 billion in 1997, the market has grown
at a 73% CAGR over the last four years.
This growth reflects several trends:
- a maturation of the long distance segment of
the DWDM equipment market
- stiffening competition that will lead to price
From 1999 to 2000
- the number of vendors offering DWDM
system-level products grew from 15 to 30
- the number of carriers that have deployed
DWDM climbed from 75 to 175.
- the number of contracts for DWDM will
double from 75 to 150.
- Such growth reflects the tremendous
demand long-distance carriers face for
transport in bandwidth.
Lucent Technologies - five-year agreement with
Bell Atlantic valued at approximately $500
million for optical networking, including
DWDM, network management software and
SONET transmission equipment.
to Dell'Oro Group, Lucent captured the
largest market share - 34 percent (or approximately
$1.3 billion) - of the $3.8 billion global DWDM
equipment market in 1999.
Lucent will install the DWDM optical networking
system in the new, 900- mile (1,300 km) route
between Xian and Wuhan which is worth more than
$10 million.
"Getting an early lead in this market will prove to
be very important," said Scott Clavenna, principal
analyst at Pioneer Consulting, which has forecast the
metro DWDM market to grow to nearly $1 billion by
Future of DWDM
What the future holds
 Two-way video communication
 Digital video for our everyday use at home and at
 Change from voice telephony to digital data
heavy with video to require multiplying
backbone transmission capacity.
 The Ultimate Squeeze
- reducing the “space” between wavelengths
- expanding the range of transmission
- better EDFAs
Develop better equipment for switching and
manipulating the various wavelengths after the
signal emerges from the optical “pipe.”
WDM is creating huge new information pipelines
that will bring better service at lower cost. But the
real information revolution won’t come until
cheap WDM pipelines reach individual
Applications of DWDM
DWDM is ready made for long-distance
telecommunications operators that use either
point-to-point or ring topologies.
Building or expanding networks
Network wholesalers can lease capacity, rather
than entire fibers.
The transparency of DWDM systems to various
bit rates and protocols.
Utilize the existing thin fiber
DWDM improves signal transmission