DENSE WAVELENGTH DIVISION MULTIPLEXING

(DWDM)

BYBY

AKASH BHARTI

EC-09

0901431007

AKASH BHARTI

EC-09

0901431007

11

Introduction Configurations of DWDM Systems Components of DWDM DWDM Design Considerations Summary

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Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs multiple light wavelengths to transmit in parallel through a single fiber.

TM16TM

16TM16TM

16

WD

M

TM16TM16TM16TM16

WD

M

STM-16

STM-16

STM-16

STM-16

4 * STM-16 = 10 Gb/s

TM16

TM16TM

16

WD

M

TM16

TM16TM16

STM-16

STM-16

STM-16

8 * STM-16 = 20 Gb/sILA

8 * STM-16 = 20 Gb/s WD

M

TM16

TM16TM

16

WD

M

TM16

TM16TM16

STM-16

STM-16

STM-16

32 * STM-16 = 80 Gb/s

OAD

32 * STM-16 = 80 Gb/s

WD

M

8

-

-

2

1

8

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2

1

32

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2

1

32

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2

1

4 Ch p-2-p system 4 Ch p-2-p system

8 Ch range extended by OA 8 Ch range extended by OA

32 Ch system with 80Gbps capacity and OAD feature32 Ch system with 80Gbps capacity and OAD feature

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• STM-1 frame

AU-n pointers

RSOH

MSOH

1 2 9 10 11 270

1

4

9

STM-1 PAYLOADPOH

125µs

C-4

VC-4AU-4

Early WDM (late 80s)Two widely separated wavelengths (1310, 1550nm)

“Second generation” WDM (early 90s)Two to eight channels in 1550 nm window400+ GHz spacing

DWDM systems (mid 90s)16 to 40 channels in 1550 nm window100 to 200 GHz spacing

Next generation DWDM systems64 to 160 channels in 1550 nm window50 and 25 GHz spacing 66

TTimeime DDivisionivision MMultiplexingultiplexing(TDM)(TDM)

SDH is the standardized TDM based hierarchial model where the following transmission rates are defined:STM-1: 155 Mbps STM-4: 622 MbpsSTM-16: 2.5 GbpsSTM-64: 10 GbpsSTM-256: 40 Gbps

number of wavelength channels number of wavelength channels > 16> 16

  DDenseense WDMWDM DWDMDWDM

SoSocombining many wavelength onto a combining many wavelength onto a

single fiber using:single fiber using:

  WWavelengthavelength DDivisionivision MMultiplexingultiplexing(WDM)(WDM)

Why WDM?

• Capacity upgrade- using existing fiber networks (without adding new fibers).

• Transparency- DWDM optical channels can carry any transmission format, supporting TDM (SDH/SONET) different asynchronous formats, ATM, Gigabit

Ethernet, ESCON, etc.

• Low initial cost- Set up with minimum configuration

• Wavelength routing and switching- Wavelength is used as another dimension to time and space.

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WDM – Features

• Fully utilizes fiber bandwidth resource

• Super-long-transmission distances (EDFA technology) • Support hybrid of transmission

formats• Easy upgrade/expansion• Saving fiber resources (more

‘s)• Utilizing TDM technology(SDH)• Forming full Optical networks

(OADM & OXC)

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WDM (Wavelength Division Multiplexing) Used two wavelengths ; one in 1310 nm window and other in 1550 nm

window, in the initial wavelength division multiplexing case.

Coarse WDM (CWDM) The CWDM technology refers to the WDM technology with large interval

(usually greater than 20 nm) between adjacent wavelengths. Usually, its wavelength quantity is 4 or 8 (16 at most). It uses 1270nm-1610 nm windows.

Dense WDM (DWDM) DWDM spaces the wavelengths more closely. Therefore, DWDM has a

greater overall capacity. DWDM common spacing may be 200, 100, 50,

or 25 GHz with a channel count reaching upto 160 channels at distances

of several thousand kilometers, with amplification and regeneration

along such a route.

Types of WDM System

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Two Variants of DWDM:

Long Haul DWDM

Basically P2P system for Long-Haul application.

Metro DWDM (Short Haul)

For Metro area application. Can be configure into a ring network complete with protection mechanism.

Variants of DWDM System

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Short-haul Solutions

• Low cost Tx transponders or SDH integrated transmitters

• Low loss Mux/Demux

D2 TRP

D2 TRP

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AUX-alarms

MUX

DEMUX100 km100 km

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• The value proposition is very different from the long haul Rapid-service provisioning Protocol/bit-rate transparency

• Metro DWDM is an emerging market for next generation

DWDM equipment

Long-haul Systems

• Longhaul Tx transponders or integrated transmitters

• Booster and preamp allows low cost mux/demux

• Remote management (OSC). Optical layer performance supervision may be included

OSC

NetworkManagement

OSCNetworkManagement

OSC

D10 TRP

D10 TRP

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Rx TRP

Rx TRP

. . . . . . . . .

640km640km

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Optical Multiplexer

Optical De-multiplexer

Optical Add/Drop Multiplexer(OADM)

Transponder

1

2

3

1

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15xx

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1...n

1...n

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Optical Amplifier(EDFA)

Optical AttenuatorVariable Optical Attenuator

Dispersion Compensator (DCM / DCU)

1616

n

MU

X

Transponder at Transmit side

n

DE

MU

X

EDFAEDFA

OADM

DWDM Network Elements

Transponder at Receive side

•A transponder-convert a wavelength to another wavelength •The wavelength converted be used by the DWDM system

Optical Add-Drop Multiplexer (OADM)Optical Add-Drop Multiplexer (OADM)

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A transponder is basically a module that can convert a wavelength to another wavelength which can be used by the DWDM system. It also

does the 3R or 2R function.

Transmit Transponder• emits one specific wavelength • perform 3Rs• Relatively high cost

Receive Transponder• accept any wavelength• perform 2Rs (generally)• Relatively lower cost

3R/2R

The 3RsRegeneration ReshapingRetiming

Transponder

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“Simple” device consisting of four parts: Erbium-doped fiber - unstable Erbium ions release energy Two optical pumps (1480/980nm) to stimulate erbium atoms

to release stored energy at 1550nm. A coupler to combines signal light and pump light An isolator to suppress reflections for stable working

Isolator Coupler IsolatorCoupler

Erbium-DopedFiber (10–50m)

PumpLaserPumpLaser

PumpLaserPumpLaser

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Pump Laser(980/1480 nm)

Optical Add-Drop Multiplexer (OADM)

1

23

n

Single

Fiber

1

23

n

Dropped s

Multi- in

Single

Fiber

Multi- out

Adding s

Demultiplexer

Local ports

Multiplexer

4

4

Transponder

• Similar to SDH ADM,except only optical wavelength are added and dropped with no O-E conversion.

• Allow adding and dropping of channels at station.

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Spectrally broad Uses LED with mirrors Unstable center/peak wavelength Low cost, used at client end of

TRP

cPower

Power c

DWDM Laser Distributed Feedback (DFB)

Non DWDM Laser Fabry Perot

• Dominant single laser line(50khz)

• Stable wavelength

• Higher power, used in DWDM

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Transmission Challenges Unidirectional vs. Bidirectional Protection

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Attenuation: Reduction of power level with distance

Dispersion and nonlinear effects: Erodes clarity with distance and speed

• Noise and Jitter: Leading to a blurred image(Jitter: Random shift in correct timing of a bit)(Jitter: Random shift in correct timing of a bit)

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DWDM systems can be implemented in two different ways

Bi -directional

Fiber

Uni -directional

Fiber

Fiber

• Uni-directional:

wavelengths for one direction travel within one fiber

two fibers needed for

full-duplex system

• Bi-directional:

a group of wavelengths for each direction

single fiber operation for full-duplex system

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Uni-directional 32 channels system

32

32

Full band

Full band

ChannelSpacing100 GHz

16

16

Blue-band

Red-band

ChannelSpacing100 GHz

16

16

• Bi-directional 32 channels system

32 chfull

duplex

16 chfull

duplex

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Network survivability => ability of a network to› continue to provide a service even after a

failure occurrence within the network

Failures in networks are bound to happen› Fiber cuts or breaks› Node failure e.g. total power failure› Wavelength channel outage e.g. faulty

transmitter› Human error e.g. incorrect configuration or

wrong unit

DWDM provides hundreds of Gbps of scalable transmission capacity today

Better use of existing fiber bandwidth

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Allows fast expansion of capacity on existing routes

‒ 32Channels@ 10Gbit/s‒ 320 Gbit/s on a single fiber pairAllows multiple clients to be carried directly

and in parallel on the same fiber Saves time & cost of laying new fibers System upgrade can maximize existing investment protectionHigh reliability and flexibility of networkingCompatible all-optical exchange

Application codesMax number of spans

Max Bit rate e.g STM-16

Fibre types; 2: G652, Standard SM

Fibre 3: G653 Dispersion shifted

fibre 5:G655 Dispersion

Flattened fibre

n W X - y, zNumber of

optical channels L (Long Haul) = 22dB span

or V (Very Long Haul) = 33dB span

e.g. 32 L 4 -16,2= 32 channels, 22dB span att., 4 spans, STM-

16, Standard Fibre

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