!day1_otc000003 Wdm Principle Issue1.22

WDM Principle www.huawei.com

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Foreword 

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.

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Page2

Objectives 

Upon completion of this course, you will be able to: 

Describe the concepts, transmission modes and structure of WDM;



Classify the different types and characteristics of the fiber;



Outline the key technologies of WDM system;



List the technical specifications for WDM system.

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Page3

Contents  WDM Overview  Transmission Media  Key Technologies  Technical Specifications

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Page4

How to increase network capacity ？

 

SDM Add fiber & equipment





WDM



Economical &



TDM

Mature &



STM-16→ STM-64

Quick



Cost & Complication

Time & cost

Solution of capacity expansion

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Page5

What's WDM ？

Gas Station

Free Way

Patrol Car

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Page6

WDM Concept 

Different signals with specific wavelength are multiplexed into a fiber for transmission.

λ1

λ1 λ2

λn

SDH signal IP package ATM cells

λ2 ┋

┉

λn

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Page7

System Structure 

The overall structure of the WDM system of N-path wavelength: 



Optical Transponder Unit (OTU) Optical Multiplexer Unit / Optical De-multiplexer Unit (OMU/ODU)



Optical Amplifier (OA)



Supervisory Channel (OSC/ESC) OTU OTU OTU

O M / O A

O A / O D

OLA

OSC

OSC

OSC

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Page8

OTU OTU OTU

Transmission Modes Single fiber unidirectional transmission MUX

O T U

M 4 0

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DMUX

M 4 0



Page9

O T U

Transmission Modes Single fiber bidirectional transmission MUX/DMU X O T U

M 4 0

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DMUX/MUX

M 4 0



Page10

O T U

Application Modes Open System MUX

O T U

DMUX

M 4 0

M 4 0



Client

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O T U Client

Page11

Application Modes Integrated System MUX

DMUX

M 4 0

M 4 0



Client

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Client

Page12

Advantages of WDM 

Ultra high capacity



Data transparency transmission



Long haul transmission



Compatible with existing optical fibers



High performance-to-cost ratio



High networking flexibility, economy and reliability



Smooth expansion

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Page13

CWDM Vs DWDM CWDM:





Coarse Wavelength Division Multiplex

DWDM:





Dense Wavelength Division Multiplex

ITU-T G.694.1

196.05THz

Extended C band 192chs, 25GHz spacing C band 160chs 192.125THz

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Extende d 32chs 192.05THz

Page14

191.275THz

Questions 

What are WDM, DWDM and CWDM?



Difference between the two transmission modes



Difference between the two application modes



List the structure of the WDM system.

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Page15

Summary 

Basic concepts and features of WDM, DWDM and CWDM;



WDM system structure ;



Transmission and application Modes of WDM system;

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Page16

Contents  WDM Overview  Transmission Media  Key Technologies  Technical Specifications

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Page17

Structure of Optical Fiber 

Consists of a cylindrical glass core, a glass cladding and a plastic wear-resisting coating. Refraction n2

Cladding

θ

Reflection

n1

Core

Coating

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Page18

Attenuation 5 4

Multi-mode

dB/km

3

1

E

S C L U

OH-

（ 850~900nm

2

O band

900

nm 1200 130014001500

） Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Page19

1600 1700

Dispersion 

Chromatic dispersion:

Power Optical pulses Transmitting L1 (km)

Transmitting L2 (km)

Time

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Page20

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

G.653: Zero dispersion at 1550nm window.

Dispersion coefficient

17ps/nm.km

G.655

1310nm

¦ Ë

1550nm

G.655: Little dispersion to avoid FWM.

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Page21

Dispersion Compensation 

The pulse will be broadened because of 



Positive dispersion coefficient at 1550nm window

DCF has negative dispersion coefficient and can counteract positive dispersion in transmission. Dispersion Coefficient

G.652

wavelength Normal DCF DSCF: Dispersion Slope Compensation Fiber Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Page22

Questions 

What’s difference between the refractive index of the cladding and core?



What are the features of G.652, G.653 and G.655 fibers?



How to compensate the chromatic dispersion?

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Page23

Summary 

Structure of optical fiber



Types of optical fiber



Characteristics of optical fiber

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Page24

Contents  WDM Overview  Transmission Media  Key Technologies  Technical Specifications

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Page25

WDM System Key Technologies



Optical Source



Optical Multiplexer and Demultiplexer

Key Tech. in WDM 

Optical Amplifier



Supervisory Technologies

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Page26

Requirements of Optical Source

1

Larger dispersion tolerance value

2

Standard and stable wavelength

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Page27

Direct modulator

LD

Modulation current

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Page28

Electro-Absorption (EA) external modulator

DC current drive

EA

LD ITU ¦ Ë

Modulation current

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Page29

Mach-Zehnder (M-Z) external modulator Modulation current

LD DC current drive

ITU ¦ Ë

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Page30

Comparison of Modulators Types

Direct Modulator

EA Modulator

Max. dispersion toleration (ps/nm)

1200~4000

7200~12800

Cost

moderate

expensive

very expensive

Wavelength Stability

good

better

best

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Page31

M-Z Modulator >12800

Optical Amplifiers

EDFA

Erbium Doped Fiber Amplifier

RFA

Raman Fiber Amplifier

OA

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Page32

Erbium Doped Fiber Amplifier E3 excited state Decay 1550nm signal light

E2 meta-stable state Stimulated radiation

1550nm signal light

980nm pump light

E1 ground state  Er3+ energy level diagram

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Page33

Structure of EDFA

Signal input

ISO

Coupler

ISO

Signal Output TAP

TAP EDF Pumping laser PD

PD

ISO: Isolator PD: Photon Detector

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Page34

Features of EDFA … Advantages

Consistent with the low



attenuation window High energy conversion



… Disadvantages

Fixed gain range



Gain un-flatness



Optical surge problem



efficiency High gain with little cross-



talk Good gain stability



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Page35

Automatic Gain Control λ1~ λn

G ain

λ1~ λn E Pin DFA Pout

Gain no change! Gain = Pout / Pin is invariable coupler

Input Power: Pin splitter PIN

pump

Output Power: Pout

EDF splitter

DSP

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PIN

Page36

Raman Fiber Amplifier 

Stimulated Raman Scattering Gain

Pump

30nm 13THz

Gain Pump1 Pump2 Pump3

30nm 70~100nm Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Page37

Features of Raman … Advantages

Flexible gain wavelength



Simple structure



Nonlinear effect can be



reduced; Low noise

… Disadvantages

High pump power, low



efficiency and high cost; Components & fiber



undertake the high power;



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Page38

Application of OA

OTU

OTU

M 4 U 0 X

OA

Booster amplifier

M OA4 0

Line Amplifier

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M OA4 0

D M M 4 0U X

OTU

OTU

Pre-amplifier

Page39

Optical Multiplexer and Demultiplexer TFF

Thin Film Filter

AWG

Arrayed Waveguide Grating

λ1 λ2

λ1 λ2

λn

λ1 λ2

λ1 λ2 λn

λn

λn Multiplexer

Demultiplexer

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Page40

Thin Film Filter

λ 1- λ 4

λ

1

filter

Self-focusing lens λ

λ

λ3 filter

2

λ λ

4

3

Glass

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Page41

1

Arrayed Waveguide Grating

Arrayed of waveguides 1…n

λ1 λ1,λ2… λn

λn Arrayed of fibers

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Page42

Supervisory Technologies

OSC

Optical Supervisory Channel Technology

ESC

Electrical Supervisory Channel Technology

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Page43

Optical Supervisory Channel Requirements: 



Operating wavelength should be different from the pumping wavelength of OA. Operating wavelength should not take 1310nm window.



Available when OA fails;



Suitable for long distance transmission. OSC

S C C

OTU1 OTU2 OTU3 OTU4

M 4 0

F I U

F I U

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OSC OTU1 OTU2 OTU3 OTU4

M 4 0



Page44

S C C

Typical frame structure of OSC TS0

TS1

TS2

TS3

……

T

T

T

……

S14

S15

S16

TS0

FA

TS17

F2 byte

TS1

E1 byte

TS18

F3 byte

TS2

F1 byte

E2 byte

TS14 TS3-TS13, TS15

ALC byte

TS19 Other s

D1-D12 bytes

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Reserved

Page45

TS31

Electrical Supervisory Channel Features:

S C C



Simple structure & cost saving



Redundancy supported



Improve power budget



Reduce system complexity

OTU1 OTU2 OTU3 OTU4

M 4 0

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OTU1 OTU2 OTU3 OTU4

M 4 0



Page46

S C C

Questions 

What is the mechanism of electro-absorption modulation?



How many types of multiplexer are there used for WDM?



What is the difference between EDFA and Raman?



What are the working wavelength and bit rate of OSC signal?

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Page47

Summary 

Optical source



Optical amplifier



Optical multiplexer



Supervisory technologies

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Page48

Contents  WDM Overview  Transmission Media  Key Technologies  Technical Specifications

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Page49

Related ITU-T recommendations 

G.652

Characteristics of a single-mode optical fiber cable



G.655

Characteristics of a dispersion-shifted SMF



G.661/G.662/G.663



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

Relevant recommendations of OA

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)



G.975

Forward error correction for submarine systems (FEC)

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Page50

Transmission Channel Reference Points

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Page51

Distribution of Optical Wavelength Areas 

Nominal central frequency refers to the central wavelength corresponding to each channel in WDM systems. Channel frequency allowed in G.692 is based on frequency and spacing series of reference frequency 193.1THz and minimum spacing 100GHz , 50GHz or 25GHz.

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Page52

Questions 

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



What is the absolute reference frequency for WDM systems?

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Page53

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