16835720 Day1otc000003 Wdm Principle Issue122

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

WDM Principle

Page2Copyright © 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.


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.


Contents

1. WDM Overview

2. Transmission Media

3. Key Technologies

4. Technical Specifications


Solution of capacity expansion

SDM

Add fiber &

equipment

Time & cost

TDM

STM-16→ STM-64

Cost &

Complication

WDM

Economical &

Mature &

Quick

How to increase network capacity？


What's WDM？

Free Way

Gas Station

Patrol Car


WDM Concept

1

2┋

1 2 n

┉

n

SDH signal

IP package

ATM cells

Different signals with specific wavelength are

multiplexed into a fiber for transmission.


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

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

DU) Optical Amplifier (OA)

Supervisory Channel (OSC/ESC)

System Structure

OTU

OTU

OTU

OM/OA

OA/OD

OTU

OTU

OTU

OSC OSCOSC

OLA


Transmission Modes

Single fiber unidirectional transmission

M40

M40

MUX DMUX

OTU

OTU


M40

M40

MUX/DMUX

DMUX/MUX

Transmission Modes

Single fiber bidirectional transmission

OTU

OTU


Application Modes

Open System

M40

M40

MUX DMUX

OTU

OTU

Client Client


Application Modes

Integrated System

M40

M40

MUX DMUX

Client Client


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


CWDM Vs DWDM

CWDM:

Coarse Wavelength Division

Multiplex

DWDM:

Dense Wavelength Division

Multiplex

Extended C band 192chs, 25GHz spacing

196.05THz 192.125THz

C band 160chs

192.05THz

Extended 32chs

191.275THz

ITU-T G.694.1


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.


Basic concepts and features of WDM, DWDM and

CWDM;

WDM system structure ;

Transmission and application Modes of WDM system;

Summary


Contents

1. WDM Overview


3. Key Technologies



Structure of Optical Fiber

Consists of a cylindrical glass core, a glass cladding

and a plastic wear-resisting coating.

θ

n2

n1

Refraction

Reflection

Cladding

Core

Coating


Attenuation

900 130014001500 1600 1700

nm

dB/km

2

3

1

4

5

1200

Multi-m

ode

（850~900nm

）

Oband

E S C L U

OH-


Dispersion

Chromatic dispersion:

Time

Power

Optical pulses

TransmittingL1 (km)

TransmittingL2 (km)


Dispersion coefficient

G.655

1550nm1310nm

17ps/nm.km

¦ Ë

Dispersion

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

G.653: Zero dispersion at 1550nm window.

G.655: Little dispersion to avoid FWM.


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

Normal DCF

DSCF: Dispersion Slope Compensation Fiber

wavelength


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?


Structure of optical fiber

Types of optical fiber

Characteristics of optical fiber

Summary


Contents

1. WDM Overview


3. Key Technologies



WDM System Key Technologies

Optical Source

Optical Amplifier Supervisory Technologies

Key Tech. in WDM

Optical Multiplexer and Demultiplexer


Requirements of Optical Source

1 Larger dispersion tolerance value

2 Standard and stable wavelength


Direct modulator

LD

Modulation current


Electro-Absorption (EA) external modulator

LD EADC current drive ITU ¦ Ë

Modulation current


DC current drive

ITU ¦ Ë

Modulation current

LD

Mach-Zehnder (M-Z) external modulator


Comparison of Modulators

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


Optical Amplifiers

EDFA

RFA Raman Fiber Amplifier

Erbium Doped Fiber Amplifier

OA


Stimulated radiationStimulated radiation

Er3+ energy level diagram

Erbium Doped Fiber Amplifier

E2 meta-stable state

E3 excited state

E1 ground state

1550nmsignal light

1550nmsignal light

980nmpump light

DecayDecay


Structure of EDFA

Coupler

EDF

ISO

Pumping laser

ISO

PD

TAP

Signal input

TAP

Signal Output

PD

ISO: Isolator

PD: Photon Detector


Features of EDFA

Consistent with the low attenuation window

High energy conversion efficiency

High gain with little cross-talk

Good gain stability

…

Fixed gain range Gain un-flatnessOptical surge problem

…Advantages Disadvantages


Automatic Gain Control

Pin Pout

Gain

λ1~ λn

λ1~ λn

Gain no change!

EDFA

PINpump

PINDSP

splitter splitter

EDFInput Power: Pin Output Power: Pout

Gain = Pout / Pin is invariablecoupler


Raman Fiber Amplifier

Stimulated Raman Scattering

PumpGain

30nm

13THz

Pump3

70~100nm30nm

GainPump2Pump1


Features of Raman

Flexible gain wavelength Simple structure Nonlinear effect can be reduc

ed;Low noise

…

High pump power, low efficiency and high cost;

Components & fiber undertake the high power;

…Advantages Disadvantages


Application of OA

Booster amplifier Line Amplifier Pre-amplifier

M40

OTU

OTU

M40

M40

OTU

OTU

M40

MUX

DMUX

OA OA OA


Optical Multiplexer and Demultiplexer

Multiplexer

λ1λ2

λn

λ1 λ2 λn

Demultiplexer

λ1λ2λn

λ1 λ2 λn

TFF

AWG Arrayed Waveguide Grating

Thin Film Filter


λ 1- λ 4

λ 4

λ 2

λ 3

Self-focusing lens

λ 1 filter

λ 3 filter

Glass

λ 1

Thin Film Filter


Arrayed Waveguide Grating

λ1,λ2… λn

Arrayed of waveguides 1…n

λ1

λnArrayed of fibers


Supervisory Technologies

OSC Optical Supervisory Channel Technology

ESC Electrical Supervisory Channel Technology


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.

M40

M40

FIU

OTU1OTU2OTU3OTU4

OTU1OTU2OTU3OTU4

FIU

OSC OSC

SCC

SCC


Typical frame structure of OSC

TS0 FA TS17 F2 byte

TS1 E1 byte TS18 F3 byte

TS2 F1 byte TS19 E2 byte

TS14 ALC byteOthers

Reserved

TS3-TS13, TS15

D1-D12 bytes

TS0 TS1 TS2 TS3 …… TS1

4

TS1

5

TS1

6

…… TS31


Electrical Supervisory Channel

Features: Simple structure & cost saving Redundancy supported Improve power budget Reduce system complexity

M40

M40

OTU1OTU2OTU3OTU4

OTU1OTU2OTU3OTU4

SCC

SCC


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?


Optical source

Optical amplifier

Optical multiplexer

Supervisory technologies

Summary


Contents

1. WDM Overview


3. Key Technologies



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 Relevant recommendations 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)

G.975 Forward error correction for submarine systems (FEC)


Transmission Channel Reference Points


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.


Questions

Which are the ITU-T recommendations involved for

WDM part?

What is the absolute reference frequency for WDM

systems?

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16835720 Day1otc000003 Wdm Principle Issue122