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Huawei Confidential. All Rights Reserved
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?
3Internal Use
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.
4Internal Use
Chapter 1 WDM OverviewChapter 1 WDM Overview
Chapter 2 WDM Transmission Media
Chapter 3 DWDM Key Technologies
Chapter 4 Technology Specifications for WDM
System
5Internal Use
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
6Internal Use
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
7Internal Use
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
8Internal Use
Free Way
Gas Station
Prowl Car
What's WDMWhat's WDM ？？
9Internal Use
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
10Internal Use
Rx1
Rxn
Rx2
Tx1
Tx2
Txn
MUX
OLA
DEMUX
OSCOSC OSC
Structure of WDM SystemStructure of WDM System
11Internal Use
Single fiber unidirectional transmission
Unidirectional WDM TransmissionUnidirectional WDM Transmission
12Internal Use
Single fiber bi-directional transmission
Bi-directional WDM TransmissionBi-directional WDM Transmission
13Internal Use
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.
14Internal Use
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.
15Internal Use
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
16Internal Use
Transparent media Long haul transmission High capacity Use existing optical fibers High performance-to-cost ratio Reliability Easy upgrading
Advantages of DWDMAdvantages of DWDM
17Internal Use
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
18Internal Use
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
19Internal Use
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.
20Internal Use
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.
21Internal Use
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
22Internal Use
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.
23Internal Use
Attenuation of Optical FiberAttenuation of Optical Fiber Attenuation of Optical FiberAttenuation of Optical Fiber
24Internal Use
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
25Internal Use
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
26Internal Use
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.
27Internal Use
QuestionsQuestions
What are the basic structures and types of optical fibers? What kinds of dispersion are there in the optical fiber?
28Internal Use
SummarySummary
In this chapter, we have learned : The basic structures and types of optical
fibers; The characteristics of optical fibers;
29Internal Use
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
30Internal Use
Optical Amplifiers
光监控技术
Optical Source
Optical Supervisory Technologies
Multiplexing and Demultiplexing
DWDM System Key TechnologiesDWDM System Key Technologies
31Internal Use
1) Larger dispersion tolerance value;
2) Standard and stable wavelength.
Requirements of Optical SourceRequirements of Optical Source
32Internal Use
1 Direct modulation 2 Electro-absorption (EA) external modulator 3 Mach-Zehnder (M-Z) external modulator
LaserLaser
33Internal Use
Output laser is controlled by input current Transmission rate≤2.5Gb/s Transmission distance≤100km
LDCurrent Laser
Direct modulationDirect modulation
34Internal Use
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)
35Internal Use
Long dispersion limited distance Low cost Negligible chirp High Dispersion tolerance
LD
Mach-Zehnder external modulatorMach-Zehnder external modulator （（ M-ZM-Z ））
36Internal Use
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
37Internal Use
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
38Internal Use
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)
39Internal Use
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
40Internal Use
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
41Internal Use
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
42Internal Use
>1dB
<0.5dB
Drop
Gain LockingGain Locking
43Internal Use
>1dB
<0.5dB
Add
Gain LockingGain Locking
44Internal Use
The Operating Theory of Raman Fiber AmplifierThe Operating Theory of Raman Fiber Amplifier
Stimulated Raman Scattering(SRS)
Pump
Gain
30nm
70~100nm
45Internal Use
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
46Internal Use
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
47Internal Use
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;
48Internal Use
Application of OAApplication of OAApplication of OAApplication of OA
According to its application:
BA-Booster amplifier
LA-Line amplifier
PA-Pre-amplifier
49Internal Use
n
n
n
n
n
n
Multilpexer Demultiplexer
Multiplexer and De-multiplexerMultiplexer and De-multiplexer
50Internal Use
Optical Grating Type DWDM ComponentOptical Grating Type DWDM Component
Periodic variation of the refractive index (grating)
Ultraviole light interference
¦ Ë1¦ Ë2¦ Ë3 ¦ Ë2
51Internal Use
λ1-4
λ4
λ2
λ3
Self-focusing lens
λ1 filter
λ3 filter
Glass
λ1
Dielectric film filter typeDielectric film filter type
52Internal Use
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
53Internal Use
Optical supervisory channelOptical supervisory channel
54Internal Use
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
55Internal Use
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
56Internal Use
O
MBA
P
A
O
D
OSCinput OSC output
OSC transmissionOSC transmission
57Internal Use
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?
58Internal Use
SummarySummary
In this chapter, we have learned: Optical source; Optical amplifier; Wave division Multiplexing Optical supervisory channel.
59Internal Use
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
60Internal Use
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
61Internal Use
Definition of Transmission Channel Reference PointsDefinition of Transmission Channel Reference Points
62Internal Use
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.
63Internal Use
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?
64Internal Use
SummarySummary
In this chapter, we have learned: Related ITU-T recommendations Distribution of Optical Wavelength Areas
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