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OTC000003 WDM PrincipleOTC000003 WDM Principle

ISSUE 1.3

2Internal Use

With the development of telecommunication, the requirements of the transmission capacity and service categories are becoming bigger and bigger, under this background, WDM technology emerged. What is WDM?

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ObjectiveObjective

After studying, you are able to… Understand and master the basic concepts

and transmission modes, structure of WDM.

Understand WDM transmission media;

Understand technical principle and key technologies of DWDM;

Understand technology specification for WDM system.

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Chapter 1 WDM OverviewChapter 1 WDM Overview

Chapter 2 WDM Transmission Media

Chapter 3 DWDM Key Technologies

Chapter 4 Technology Specifications for WDM

System

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1. Basis for Optical Communication

2. Guide to DWDM Technologies

3. DWDM Transmission System Principle and Testing

4. High Speed Optical Communication ITU-T Specification and System Design

5. Metropolitan Area Fiber Network

…………….

ReferencesReferences

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1.Growth of voice ,data ,new services

2.Desire for information ,communication

1.Developed rapidly :

4×2.5Gb/s→32×10Gb/s→1.6Tb/s

2.Developing trend: OADM , OXC…

Development of DWDMDevelopment of DWDM

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SDM － add fiber, equipment （ time &cost）

How to increase network capacityHow to increase network capacity ？？

High rate TDM signal STM-1→STM-64→

DWDM is a quick, economical and mature method

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Free Way

Gas Station

Prowl Car

What's WDMWhat's WDM ？？

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Different signals with specific

wavelength are multiplexed into

a fiber for transmission

SDH signal

IP package

ATM cells

1

2

┋

1 2 n

┉

WDM ConceptWDM Concept

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Rx1

Rxn

Rx2

Tx1

Tx2

Txn

MUX

OLA

DEMUX

OSCOSC OSC

Structure of WDM SystemStructure of WDM System

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Single fiber unidirectional transmission

Unidirectional WDM TransmissionUnidirectional WDM Transmission

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Single fiber bi-directional transmission

Bi-directional WDM TransmissionBi-directional WDM Transmission

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Application modes-open systemApplication modes-open systemApplication modes-open systemApplication modes-open system

OTU OTUDMUX MUX

Optical amplifier

OSC

Acc

ess

chan

nels

Open WDM system has no special requirements for multiplex term

inal optical interfaces, the only requirement is that these interfaces

meet the optical interface standards defined in ITU-T.

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Application modes-integrated systemApplication modes-integrated systemApplication modes-integrated systemApplication modes-integrated system

DMUX MUX

Optical amplifier

OSC

Acc

ess

chan

nels

Integrated WDM system does not adopt the wavelength conversion te

chnology, instead, it requires that the wavelength of the optical signals

at the multiplex terminal conforms to the specifications for the WDM s

ystem.

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WDM System CompositionsWDM System Compositions

The overall structure of the WDM system of N-path wavelength: Optical wavelength conversion unit (OTU) Optical De-multiplexer Unit / optical Multiplexer Unit (ODU/OMU) Optical Amplifier ( OA) Optical Supervisory Channel ( OSC)

OSC

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Transparent media Long haul transmission High capacity Use existing optical fibers High performance-to-cost ratio Reliability Easy upgrading

Advantages of DWDMAdvantages of DWDM

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Brief Introduction to CWDMBrief Introduction to CWDM

CWDM（ Coarse Wavelength Division Multiplex）

Difference between CWDM and DWDM: Carrier channel spacing of CWDM is wide; CWDM modulate laser adopts the uncooled laser,; The CWDM currently used generally works from 1260nm band to 1620

nm, the spacing is 20nm, and can multiplex 16 wavelength channels. The CWDM greatly reduces the system cost while providing certain am

ount of wavelength and transmission distance within 100 kilometers

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TDM in electric domain FDM in optics domain Backbone Long haul & MAN Protocol oriented Transparent

SDH WDMSDH WDMSDH WDMSDH WDM

SDH Vs WDMSDH Vs WDM

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QuestionsQuestions

1. What are WDM, DWDM and CWDM?

2. Briefly introduce two transmission modes of WDM equipment.

3. What is the open and integrated system?

4. Briefly introduce the composition of the WDM system.

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SummarySummary

In this chapter, we have learned : The basic concepts and principle of WDM

technologies; The development of WDM technologies; The working modes, structures and

characteristics of WDM system.

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Chapter 1 WDM Overview

Chapter 2 WDM Transmission MediaChapter 2 WDM Transmission Media

Chapter 3 DWDM Key Technologies

Chapter 4 Technology Specifications for WDM

System

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Structure of Optical FiberStructure of Optical FiberStructure of Optical FiberStructure of Optical Fiber

Coating Cladding Core

n2 n1

Optical fiber consists of a cylindrical glass core, a glass

cladding and a plastic wear-resisting coating.

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Attenuation of Optical FiberAttenuation of Optical Fiber Attenuation of Optical FiberAttenuation of Optical Fiber

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DispersionDispersion

Input laser is not monochromatic, it is composed of many wavelength or colour.

The different wavelengths arrive at different times to BROAD, smeared, or DISPERSED output pulse.

The chromatic dispersion in the fiber causes different wavelengths to travel at different speeds, and propagation delay.

Inputlaser

Optical

receiver

L

DATA IN DATA OUT

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Dispersion coefficient(ps/nm¡ ¤km)

G.655 fiber with positivedispersion coefficient

G.653 fiber

Wavelength¦ Ë(nm)1550

1310

G.652 fiber17

G.655 fiber with negativedispersion coefficient

G.652:widely used, need dispersion compensation for high rate transmission

1.Least attenuation & dispersion at 1550nm windows, suitable for DWDM.avoid FWM effectively2.TrueWave fiber, LEAF, etc.

G.653: Zero dispersion at 1550nm windows.

DispersionDispersion

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Dispersion CompensationDispersion Compensation

The pulse will be broadened because of positive dispersion coefficient positive dispersion slope at 1550nm

DCF has negative dispersion coefficient ， it can counteract positive dispersion in transmission.

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QuestionsQuestions

What are the basic structures and types of optical fibers? What kinds of dispersion are there in the optical fiber?

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SummarySummary

In this chapter, we have learned : The basic structures and types of optical

fibers; The characteristics of optical fibers;

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Chapter 1 WDM Overview

Chapter 2 WDM Transmission Media

Chapter 3 DWDM Key TechnologiesChapter 3 DWDM Key Technologies

Chapter 4 Technology Specifications for WDM

System

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Optical Amplifiers

光监控技术

Optical Source

Optical Supervisory Technologies

Multiplexing and Demultiplexing

DWDM System Key TechnologiesDWDM System Key Technologies

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1) Larger dispersion tolerance value;

2) Standard and stable wavelength.

Requirements of Optical SourceRequirements of Optical Source

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1 Direct modulation 2 Electro-absorption (EA) external modulator 3 Mach-Zehnder (M-Z) external modulator

LaserLaser

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Output laser is controlled by input current Transmission rate≤2.5Gb/s Transmission distance≤100km

LDCurrent Laser

Direct modulationDirect modulation

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Vo

lta

ge a

pp

lied

Support long haul transmission (2.5Gb/s >600km) Less chirp High Dispersion tolerance(2.5Gb/s :7200~12800ps/nm) High reliability

LD EA

Electro-absorption (EA)Electro-absorption (EA)

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Long dispersion limited distance Low cost Negligible chirp High Dispersion tolerance

LD

Mach-Zehnder external modulatorMach-Zehnder external modulator （（ M-ZM-Z ））

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Types Direct Modulator

EA Modulator M-Z Modulator

Max.dispersion toleration

(ps/nm)

1200~4000 7200~12800 >12800

Cost moderate expensive Very expensive

Wavelength Stability

good better best

Comparision of ModulationComparision of Modulation

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Raman Fiber Amplifier (RFA)Raman Fiber Amplifier (RFA)

Erbium Doped Fiber Amplifier (EDFA)Erbium Doped Fiber Amplifier (EDFA)

Semiconductor Optical Amplifier (SOA)Semiconductor Optical Amplifier (SOA)

Optical AmplifiersOptical Amplifiers

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EDFA energy level diagramEDFA energy level diagram

PumpE2 meta-stable state

E3 excited state

1550nm

E1 ground state

1550nm

Decay

light

signal lightsignal light

Erbium-doped Optical Fiber Amplifier Erbium-doped Optical Fiber Amplifier (EDFA)(EDFA)

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Typical internal structure of EDFATypical internal structure of EDFATypical internal structure of EDFATypical internal structure of EDFA

WDM

EDF

ISO

Pumping laser

WDM

ISO

Pumping laser

Signal output

EDF

PD

Optical isolator

Optical coupler

PD Optical detector

TAP

TAP

Signal inputOptical splitter

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Major advantages of EDFA: Its working wavelength is consistent with the minimum attenuation window

of the monomode optical fiber . High coupling efficiency. High energy conversion efficiency. High gain, low noise figure, large output power and minimum cross-talk. Stable gain characteristics .

Major disadvantages of EDFA: The gain wavelength range is fixed Gain bandwidth unflatness . Optical surge problem:.

Advantages and Disadvantages of EDFAAdvantages and Disadvantages of EDFA

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Cascading amplification of amplifier gain unflatness

Cascading amplification of amplifier gain flatness

Impact of Gain Flatness in Long Haul TransmissionImpact of Gain Flatness in Long Haul Transmission

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>1dB

<0.5dB

Drop

Gain LockingGain Locking

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>1dB

<0.5dB

Add

Gain LockingGain Locking

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The Operating Theory of Raman Fiber AmplifierThe Operating Theory of Raman Fiber Amplifier

Stimulated Raman Scattering(SRS)

Pump

Gain

30nm

70~100nm

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Characteristics of Raman Fiber AmplifierCharacteristics of Raman Fiber Amplifier

Its gain wavelength is determined by the pumping light wavelength.

The gain medium is the transmission fiber itself. Low noise .

PUMP1 PUMP3

70~100nm30nm

GAINPUMP2

EDFA

Span 1

Raman Pump

transmittingReceiving

EDFA

Span k

Raman Pump

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Advantages of RFAAdvantages of RFA

Advantages: Gain wavelength is determined by the pumping light wavelength Simple structure of amplifier Nonlinear effect can be reduced Low noise

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Disadvantages of RFADisadvantages of RFADisadvantages of RFADisadvantages of RFA

Disadvantages:

High pump power,low efficiency and high cost;

Instantaneous gain,adopting backward pump fashion;

Optical components and optical fiber undertake high optical

power;

Characteristics of gain online are not consistent;

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Application of OAApplication of OAApplication of OAApplication of OA

According to its application:

BA-Booster amplifier

LA-Line amplifier

PA-Pre-amplifier

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n

n

n

n

n

n

Multilpexer Demultiplexer

Multiplexer and De-multiplexerMultiplexer and De-multiplexer

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Optical Grating Type DWDM ComponentOptical Grating Type DWDM Component

Periodic variation of the refractive index (grating)

Ultraviole light interference

¦ Ë1¦ Ë2¦ Ë3 ¦ Ë2

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λ1-4

λ4

λ2

λ3

Self-focusing lens

λ1 filter

λ3 filter

Glass

λ1

Dielectric film filter typeDielectric film filter type

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λ 1 λ 2¡ ¡

Wavegui degrati ng

Free space

Fan- l i kewavegui de

Fan- l i kewavegui de

Small spacingLarge number of channels Flat pass-band

Integrated Optical Waveguide type :AWGIntegrated Optical Waveguide type :AWG

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Optical supervisory channelOptical supervisory channel

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Transmit related management , supervision information Operating wavelength 1510nm Monitoring rate:2Mb/s add/extract

Requirement :Not limit pumping wavelength of OA ,not limit 1310nm service ,available when OA fails ,long distance transmission

OSC technologyOSC technology

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TS0: FAS

TS1:E1

TS2:F1 TS3-TS14:D1-D12(DCC channel)

TS15:E2

TS16-TS31:reserved

0 1 3114 15 162 3

Typical frame structure of OSCTypical frame structure of OSC

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O

MBA

P

A

O

D

OSCinput OSC output

OSC transmissionOSC transmission

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QuestionsQuestions

1. What are electro-absorption laser modulation scheme and M-Z modulation scheme?

2. How many types are there for the wavelength division multiplexer? What are their individual characteristics?

3. Which are the kinds of optical amplifiers? Describe gain flat control and gain lock of EDFA.

4. What are optical supervisory channel wavelength and supervisory rate of DWDM?

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SummarySummary

In this chapter, we have learned: Optical source; Optical amplifier; Wave division Multiplexing Optical supervisory channel.

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Chapter 1 WDM Overview

Chapter 2 WDM Transmission Media

Chapter 3 DWDM Key Technologies

Chapter 4 Technology Specifications for WDM Chapter 4 Technology Specifications for WDM

SystemSystem

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G.652 Characteristics of a single-mode optical fiber cable

G.655 Characteristics of a dispersion-shifted SMF

G.661/G.662/G.663… Relevant recommendation of OA

G.671 Characteristics of passive optical components

G.957 Optical interfaces relating to SDH system

G.691 Optical interfaces for single channel STM-64,

STM-256 systems and other SDH systems with OA

G.692 Optical interfaces for multi-channel systems with OA

G.709 Interfaces for the optical transport network (OTN)

Related ITU-T recommendationsRelated ITU-T recommendations

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Definition of Transmission Channel Reference PointsDefinition of Transmission Channel Reference Points

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Distribution of Optical Wavelength AreasDistribution of Optical Wavelength Areas

A fiber has two long wavelength and low loss windows, 1310nm window and 1550nm window. But the commonly used working wavelength range for the erbium-doped optical amplifier is 192.1-196.1THz.Therefore the working wavelength area for wavelength division multiplexing system is 192.1-196.1THz.

Nominal central frequency refers to the central wavelength corresponding to each channel in optical wavelength division multiplexing systems. Channel frequency allowed in G.692 is based on frequency and spacing series of reference frequency 193.1THz and minimum spacing 100GHz or 50GHZ.

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QuestionsQuestions

1. Which are the ITU-T recommendations involved for WDM part?

2. What is the absolute reference frequency for optical wavelength

division multiplexing systems? What is their channel spacing?

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SummarySummary

In this chapter, we have learned: Related ITU-T recommendations Distribution of Optical Wavelength Areas

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