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Transcript of 01-Wdm Principle Issue1.21
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Internal
OTC000003
WDM Principle
ISSUE 1.21
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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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Upon completion of this course, you will be 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 WDM;
Understand technology specification for WDM system.
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Chapter 1 WDM Overview
Chapter 2 WDM Transmission Media
Chapter 3 WDM Key Technologies
Chapter 4 Technology Specifications for
WDM System
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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 DWDM
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SDM-add fiber, equipment(time &cost)
How to increase network capacity?
High rate TDM signal STM-1→STM-16→ STM-64
WDM is a quick, economical and mature method
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What's WDM?
Free Way
Gas Station
Patrol Car
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WDM Concept
Different signals with specific wavelength are multiplexed into a fiber
for transmission.
1
2
┋
1 2 n
┉
n
SDH signal
IP package
ATM cells
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WDM System Compositions
The overall structure of the WDM system of N-path wavelength:
Optical wavelength transponder unit (OTU)
Optical Multiplexer Unit / optical De-multiplexer Unit (OMU/ODU)
Optical Amplifier (OA)
Optical Supervisory Channel (OSC/ESC)
O
M
/
O
A
OLA
O
A
/
O
D
OTU
OTU
OTU
OTU
OTU
OTU
OSC OSC OSC
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Transmission modes – Unidirectional transmission
MUX DMUX
Single fiber unidirectional transmission
O
T
U
O
T
U
STATION A STATION B
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Transmission modes - Bi-directional transmission
Single fiber bi-directional transmission
STATION A STATION B
MUX/DMUX DMUX/MUX
O
T
U
O
T
U
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Application modes - Open system
DMUX MUX
Optical amplifier
A c c e s s
c h a n n e l s
Open WDM system has no special requirements for multiplexterminal optical interfaces, the only requirement is that these
interfaces meet the optical interface standards defined in ITU-T.
O
TU
O
TU
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Application modes - Integrated system
Integrated WDM system does not adopt the wavelength conversiontechnology, instead, it requires that the wavelength of the optical
signals at the multiplex terminal conforms to the specifications for
the WDM system.
DMUX MUX
Optical amplifier
A c c e s s
c h a n n e l s
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Advantages of DWDM
Transparent media
Long haul transmission
High capacity
Use existing optical fibers
High performance-to-cost ratio
Reliability
Easy upgrading
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Brief Introduction to CWDM
CWDM (Coarse Wavelength Division Multiplex)
The CWDM greatly reduces the system cost while providing certain
amount of wavelengths and transmission distance within 100 km.
Difference between CWDM and DWDM:
Types CWDM DWDM
Channel Spacing 20nm 0.4nm or 0.8nm
Wavelength Range 1311~1611nm C-band: 1529nm~1561nm
L-band: 1570nm~1603nm
Transmission Capacity 16 * 2.5Gb/s = 40G 160 * 10Gb/s = 1600G
Laser Uncooled Laser Cooled Laser
Cost 30% expensive
Application 100km 4000km
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Questions
What are WDM, DWDM and CWDM?
Briefly introduce two transmission modes of WDM equipment.
What is the open and integrated system?
Briefly introduce the composition of the WDM system.
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Summary
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 Media
Chapter 3 WDM Key Technologies
Chapter 4 Technology Specifications for
WDM System
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Structure 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 Fiber
A t t e n u a t i o n
( d B / k m )
1dB/km
2dB/km
3dB/km
4dB/km
5dB/km
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Dispersion
Input laser is not
monochromatic, it is
composed of many
wavelengths 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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1.Least attenuation & dispersion at
1550nm windows, suitable for DWDM,
avoid FWM effectively;
2.TrueWave fiber, LEAF, etc.
Dispersion coefficient
(ps/nm¡ ¤km)
G.655 fiber with positivedispersion coefficient
G.653 fiber
Wavelength¦ Ë(nm)
1550
1310
G.652 fiber 17
G.655 fiber with negativedispersion coefficient
G.652:widely used, needdispersion compensation
for high rate transmission
G.653: Zero dispersion
at 1550nm windows.
Dispersion
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Dispersion 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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Summary
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 WDM Key Technologies
Chapter 4 Technology Specifications for WDM System
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Optical Source Optical Supervisory
Technologies
WDM System Key Technologies
Optical Amplifiers Multiplexer andDemultiplexer
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1) Larger dispersion tolerance value;
2)Standard and stable wavelength.
Requirements of Optical Source
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Laser
Direct modulation
Electro-absorption (EA) external modulator
Mach-Zehnder (M-Z) external modulator
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Direct modulation
Output laser is controlled by input current
Transmission rate≤2.5Gb/s
Transmission distance≤100km
modulation
current
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Electro-absorption (EA) external modulator
Support long haul transmission (2.5Gb/s > 600km)
Less chirp
High Dispersion tolerance(2.5Gb/s: 7200~12800ps/nm)
High reliability
modulation
current
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LD
Mach-Zehnder (M-Z) external modulator
Long dispersion limited distance
High cost
Negligible chirp
High dispersion tolerance
modulationcurrent
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Comparision of Modulation
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
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Raman Fiber Amplifier (RFA)
Erbium Doped Fiber Amplifier (EDFA)
Semiconductor Optical
Amplifier (SOA)
Optical Amplifiers
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Stimulated radiation
Er 3+ energy level diagram
Erbium-doped Optical Fiber Amplifier (EDFA)
E2 meta-stable state
E3 excited state
E1 ground state
1550nmsignal light
1550nmsignal light
980nmpump light
Decay
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Typical 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 input Optical splitter
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Major disadvantages of EDFA:
The gain wavelength range is fixed.
Gain bandwidth unflatness.
Optical surge problem.
Advantages and Disadvantages of EDFA
Major advantages of EDFA:
Its working wavelength is consistent with the minimum
attenuation window of the mono-mode optical fiber .
High coupling efficiency.
High energy conversion efficiency.High gain, large output power and minimum cross-talk.
Stable gain characteristics.
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Cascading amplification of amplifier gain unflatness
Cascading amplification of amplifier gain flatness
Impact of Gain Flatness in Long Haul Transmission
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>1dB
<0.5dB
Drop
Gain Locking
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>1dB
<0.5dB
Add
Gain Locking
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The Operating Theory of Raman Fiber Amplifier
Stimulated Raman Scattering
(SRS)
Pump
Gain
30nm
13THz (~100nm)
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Characteristics 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
70~100nm
30nm
GAIN
PUMP2
EDFA
Span 1
Raman Pump
transmittingReceiving
EDFA
Span k
Raman Pump
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Major disadvantages of RFA:
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.
Advantages and Disadvantages of RFA
Major advantages of RFA:
Gain wavelength is determined by the pumping light wavelength;
Simple structure of amplifier;
Nonlinear effect can be reduced;
Low noise.
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Application 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-multiplexer
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Optical Grating Type DWDM Component
Periodic variation of the refractive index (grating)
Ultraviolet light interference
¦ Ë1¦ Ë2¦ Ë3 ¦ Ë2
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λ 1-4
λ 4
λ 2
λ 3
Self-focusing lens
λ 1 filter
λ 3 filter
Glass
λ 1
Dielectric film filter type
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λ1 λ2¡ -¡ -
Waveguide
grating
Free space
Fan-like
waveguide
Fan-like
waveguide
Integrated Optical Waveguide type: AWG
Small spacing
Large number of channels
Flat pass-band
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1)Optical Supervisory Technologies(OSC)
2)Electrical Supervisory Technologies(ESC)
Optical Supervisory Technologies
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Optical Supervisory Channel (OSC)
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
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0 1 3114 15 162 3
Typical frame structure of OSC
TS0: Frame alignment signal
TS1: E1 byte
TS2: F1 byte
TS3-TS13, TS15: D1-D12 bytes
TS14: ALC byte
TS17: F2 byte
TS18: F3 byte
TS19: E2 byte
Others: Reserved
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OSC transmission
O
M
B
A
P
A
O
D
OSC input OSC output
F
IU
F
IU
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Electrical Supervisory Channel (ESC)
The optical transponder unit (OTU) multiplexes the supervisory
information into the service channel for transmission.
The ESC reduces the investment of the OSC. It also deletes the
insertion loss of the FIU. This lowers the cost and the power budget
of optical channels.
A
B
C
D
NMSA
B
C
D
NMS
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Questions
What are electro-absorption laser modulation scheme. How many types are there for the wavelength division multiplexer?
What are their individual characteristics?
Which are the kinds of optical amplifiers? Describe gain flat control
and gain lock of EDFA.
What are optical supervisory channel wavelength and supervisory
rate of DWDM?
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Summary
In this chapter, we have learned:
Optical source;
Optical amplifier;
Wavelength division Multiplexer;
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 System
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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)
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Definition of Transmission Channel Reference Points
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Distribution 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 EDFA is 192.1-196.1THz. Therefore the
working wavelength area for DWDM system is 192.1-196.1THz.
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 spacingseries of reference frequency 193.1THz and
minimum spacing 100GHz or 50GHz.
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Questions
Which are the ITU-T recommendations involved for WDM part?
What is the absolute reference frequency for WDM systems? What
is their channel spacing?
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Summary
In this chapter, we have learned:
Related ITU-T recommendations
Distribution of Optical Wavelength
Areas