training course wdm principle v1.0-20080902
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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
WDM Principle
Yangmingzhang 42198
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.
Page3Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page4Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. WDM Overview
2. Transmission Media
3. Key Technologies
4. Master Limitation of DWDM system
5. Technical Specifications
Page5Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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?
Page6Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
What's WDM?
Free Way
Gas Station
Patrol Car
Page7Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page8Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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)
System Structure
OTU
OTU
OTU
OMU
ODU
OTU
OTU
OTU
OSC OSCOSC
LABA PA
Page9Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Transmission Modes
Single fiber unidirectional transmission
M40
M40
MUX DMUX
OTU
OTU
Page10Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
M40
M40
MUX/DMUX
DMUX/MUX
Transmission Modes
Single fiber bidirectional transmission
OTU
OTU
Page11Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Application Modes
Open System
M40
M40
MUX DMUX
OTU
OTU
Client Client
Page12Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Application Modes
Integrated System
M40
M40
MUX DMUX
Client Client
Page13Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page14Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
CWDM vs. DWDM
CWDM: Coarse wavelength
division multiplexing
spacing of two adjacent
wavelengths: 20 nm
192 wavelengths at the extended C band with 25 GHz channel spacing
196.05THz 192.125THz
160 wavelengths at C band
192.05THz
32 extended wavelengths
191.275THz
ITU-T G.694.1
DWDM: dense wavelength division multiplexing
spacing of two adjacent wavelengths: 25 GHz
Page15Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page16Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page17Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Basic concepts and features of WDM, DWDM and
CWDM;
WDM system structure ;
Transmission and application Modes of WDM system;
Summary
Page18Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. WDM Overview
2. Transmission Media
3. Key Technologies
4. Master limitation of DWDM system
5. Technical Specifications
Page19Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page20Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Characteristics of Fiber
Loss
Dispersion
Non-linear
Page21Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Characteristics of Fiber Loss
Fiber loss is classified into:
Absorption loss
Scattering loss
Bending loss
The fiber loss can be calculated according to the
following formula:
Fiber loss (dB) = fiber length (km) x fiber loss
coefficient (dB/km)
Page22Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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-
Attenuation varies with wavelengths. The attenuation around 1380 nm goes up sharply due to absorption by hydroxyl ions. This is generally
called "water peak". As we can see, the attenuation in C band and F band is the lowest.
Page23Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Wavelength Ranges in WDM
Band Description Range (nm) Bandwidth (nm)
O band Original 1260–1360 100
E band Extension 1360–1460 100
S band Short 1460–1525 65
C band Normal 1525–1565 40
L band Long 1565–1625 60
U band Ultra-long 1625–1675 50
In a DWDM system, C band and L band are used because the attenuation in the two bands is the lowest.
In a CWDM system, multiple bands are used, ranging from 1311 to 1611 nm, because attenuation is not a major restrictive factor in short-distance transmission.
Page24Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Fiber dispersion can be classified into:
Mode dispersion
Chromatic dispersion
Polarization mode dispersion
Dispersion: a physical phenomenon of signal distortion
caused when various modes carrying signal energy or
different frequencies of the signal have different group
velocity and disperse from each other during propagation.
Characteristics of Fiber Dispersion
Page25Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Chromatic Dispersion
Chromatic dispersion: pulse broadening, cause intersymbol interference
The chromatic dispersion can be calculated according to the following formula:
CD (ps/nm) = fiber length (km) x CD coefficient (ps/km.nm)
Time
Power
Optical pulses
TransmittingL1 (km)
TransmittingL2 (km)
Page26Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
PMD
PMD occurs when optical signals in two orthogonal polarizations travel at different speeds in optical fibers. PMD is one of critical parameters related to optical fibers.
PMD occurs randomly. So it is a random variable.
PMD has the same impact as CD has: resulting in pulse broadening.
Page27Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
According to ITU-T, three types of single-mode optical fibers are defined in G.652, G.653, and G.655 respectively. The differences between them are shown in the following table:
TypeDefinition Scope Main Specifications
G.652
The standard single-mode fiber (SMF) refers to the fiber whose zero-dispersion point (the zero-dispersion wavelength) is near to 1310 nm.
Used in both SDH system and DWDM system
Attenuation: The attenuation value of the 1310 nm band is 0.3––0.4 dB/km and the typical value is 0.35 dB/km. The attenuation value of the 1550 nm band is 0.17––0.25 dB/km and the typical value is 0.20 dB/km.Dispersion: The allowed value of the zero-dispersion wavelength is 1300––1324 nm. The dispersion coefficient of the 1550 nm band is positive and the typical value of the dispersion coefficient D is 17 ps/(nm.km). The maximum value is not more than 20 ps/(nm.km).
G.653
Dispersion-shifted fiber (DSF) refers to the fiber whose zero-dispersion point is near to 1550 nm. Compared with G.652 SMF, the zero-dispersion point of G.653 DSF shifts.
Used in the SDH system but not in the DWDM system
Attenuation: The attenuation value of the 1310 nm band is less than 0.55 dB/km and the typical value has not been confirmed. The attenuation value of the 1550 nm band is less than 0.35 dB/km and the typical value is 0.19––0.25 dB/km.Dispersion: The wavelengths in the G.653 DSF are near to 1550 nm, usually 1525––1575 nm. The maximum dispersion coefficient is 3.5 ps/(nm.km). The dispersion coefficient in the DSF is too small or may be 0 for 1550 nm bands, especially C band.
G.655
Non-zero dispersion-shifted fiber (NZDSF) refers to the fiber whose zero-dispersion point is shifted away from 1550 nm and not within the DWDM operating wavelength range near to 1550 nm.
Used in both SDH system and DWDM system, but more applicable to the DWDM system
Attenuation: The attenuation value of the 1310 nm band is not specified in ITU-T. The attenuation value of the 1550 nm band is less than 0.35 dB/km, usually 0.19––0.25 dB/km.Dispersion: If 1530 nm < < 1565 nm, 0.1 ps/(nm.km) < |D(λ)| < 6.0 ps/(nm.km). The typical value of the dispersion coefficient of the G.655 NZDSF varies with vendors and needs to be confirmed based on actual situations, usually 4.5 ps/(nm.km) and 6 ps/(nm.km).
G.652/G.653/G.655 Single-Mode Optical FibersG.652/G.653/G.655 Single-Mode Optical Fibers
Page28Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page29Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Non-Linear Effects of Single-Mode Optical Fibers
Fiber Non-linear effects can be classified into: Stimulated non-flexible scattering: stimulated Raman scattering (S
RS) and stimulated Brillouin scattering (SBS) Kerr-effect: self-phase modulation (SPM), cross-phase modulation
(XPM) and four wave mixing (FWM)
Page30Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
SRS
Short wavelength, pump, and long wavelength
Impacts on the system:
Power unbalance in the channel
Inter-channel Raman crosstalk
l
P
l
P
Input Output
Page31Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
SBS
• A non-linear phenomenon causing the strong forward transmission signal converted to backward transmission when the signal optical power exceeds the SBS threshold
• SBS power threshold: 9 dBm for single wavelength channel
Impacts on the system:
When the value exceeds the threshold, strong backward scattering is caused and intensity noise is repeated.
Page32Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
XPM/SPM
Self-Phase Modulation (SPM)The phase varies with the strength of light and is transformed into waveform distortion.
The impact varies directly with incident power in the channel and is accumulated along the fiber and transmission sections.
Cross-Phase Modulation (XPM)Phase modulation is affected by other channels and the change of phase due to fiber dispersion causes intensity noises.
Increase the channel spacing to suppress XPM.
Page33Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
FWMDefinition: Two or three lightwaves with different wavelength interact with each other, which causes new lightwaves at other wavelengths or causes new optical wavelength effect on the sideband.
Fiber
f1
ff3 f2
f1
ff3 f2fFWM
Impacts: When the new frequency generated by FWM is within the channel bandwidths, the channel strength may fluctuate and inter-channel crosstalk may occur.
Factors: dispersion, channel number, channel spacing and signal power
Page34Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Note!
Non-linear effects cannot be eliminated or
compensated for. So they should be restricted as
much as possible!
Page35Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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?
What problems may occur when optical signals are transmitted in
single-mode fibers?
Page36Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Structure of optical fiber
Types of optical fiber
Characteristics of optical fiber
Summary
Page37Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. WDM Overview
2. Transmission Media
3. Key Technologies
4. Master limitation of WDM system
5. Technical Specifications
Page38Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
WDM System Key Technologies
Optical Source/receiver
Optical Amplifier Supervisory Technologies/code technology
Key Tech. in WDM
Optical Multiplexer and Demultiplexer
Page39Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Requirements of Optical Source
1 Larger dispersion tolerance value
2 Standard and stable wavelength
Page40Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Direct modulator
LD
Modulation current
Page41Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Electro-Absorption (EA) external modulator
LD EADC current drive ITU ¦ Ë
Modulation current
Page42Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
DC current drive
ITU ¦ Ë
Modulation current
LD
Mach-Zehnder (M-Z) external modulator
Page43Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page44Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Wavelength Tunable Technology
Wavelength Tunable Principle The wavelengths corresponding to the refractive index and
maximum gain of semiconductor materials vary with the
temperature, pressure, carrier potency, and field strength. Changing
these factors can realize tunable wavelengths.
Change the temperature and carrier potency and then combine with
such technologies as MEMS, microelectronics, and lightwave circuits
to produce various tunable technologies.
Advantages of Wavelength Tunable Technology Reduction of spare parts stock
Flexible networking
Page45Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Classification of Wavelength Tunable Sources
Based on the number of tunable wavelengths: 4-wavelength, 8-wavelength, 20-wavelength, 40-wavelength, 80-
wavelength, 160-wavelength…
Based on the frequency spacing: 100 GHz, 50 GHz, and 25 GHz
Based on the appearance and structure Laser type: the appearance is similar to a common laser.
Module type: tunable laser + locker + control circuit
Based on the manufacturers Fujitsu, ioLon, Agility, Intel, BandWidth9, Princeton Optronics,
Bookham, GTRAN, QDI, Santur, Vitesse…
Page46Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Wavelength Tunable Technology
Thermally tune single DFB (~3nm tuning)
Tunable DBR
SGDBR (eg Agility)
GCSR (eg Altitun)
External cavity (Iolon)
Integrated DFB (NEC)
Electrically pumped MEMs-VCSEL ( BW9)
Optically pumped MEMs-VCSEL (Coretek)
MEMs-DFB array (Santur)
Page47Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Code Modulation Technology
Simple, low-cost, and mature
NRZ for transitional code elements, sensitive to transmission damage, and inapplicable to high-speed ultra-long-haul DWDM transmission
Commonly applied in mid- and short-haul DWDM transmission systems
… …Conventional code modulation technology (NRZ)
New code modulation technology
Reduce OSNR tolerance.
Add dispersion tolerance and
PDM tolerance.
Suppress pulse distortion
caused by non-linear effect of
the fiber.
Applied in long-haul DWDM
transmission systems.
CRZ, DRZ, ODB, DQPSK……
Page48Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Comparison of coding technologies with 10 Gbit/s rate
Coding Technology Advantage Disadvantage Application
NRZ
Narrow spectral widthSimple structure of modulation and demodulationLow cost
Low ability to prevent non-linear effects High OSNR tolerance Low dispersion tolerance
Applied to the system with 10 Gbit/s or lower rate and to short-and-medium distance transmission
SuperCRZ
Great ability to prevent non-linear effectsLower OSNR tolerance than that of NRZ
Wide spectrum bandwidthDoes not support 25 GHz systemLow dispersion toleranceDoes not support wavelength adjustable
Applied to the system with 10 Gbit/s and to long-distance transmission
SuperDRZ
Narrow spectrum bandwidthSupports 25 GHz systemHigh dispersion toleranceGreat ability to prevent non-linear effectsSupports wavelength adjustableCost effective
Applied to the system with 10 Gbit/s and to long-distance transmission
ODB
High dispersion toleranceGreat ability to prevent non-linear effectsSupports wavelength adjustable
If the optical power of signals that are just transmitted into the optical fiber is great, the transmission distance decreases because of dispersion limited. The ODB is not applied to long-distance transmission.
Applied to 10 Gbit/s metropolitan area network
Page49Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Comparison of coding technologies with 40 Gbit/s rate
COMPARE ITEM NRZ ODB DRZ ( HW)
NRZ-
DPSK
RZ-
DQPSK
DP-QPSK
OSNR ★ ★ ★★ ★★★ ★★★ ★★★★
CD tolerance ★★ ★★★ ★★ ★★ ★★★ ★★ ★★
PMD tolerance ★ ★★ ★★ ★★ ★★★ ★★ ★★
$$ ★★★★ ★★★★ ★★★ ★★ ★★ ★
50GHz × √ × × √ √
Non-linear
tolerance
★★ ★★ ★★★ ★★★ ★★ ★
Page50Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Receiver
PIN lower sensitivity (usually about -20 dBm) and higher overload point
(usually about 0 dBm); applicable to short-distance transmission
APD higher sensitivity (usually about -28 dBm) and lower overload point
(usually about -9 dBm); applicable to long-distance transmission
Page51Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
FEC Technology
Forward Error Correction Technology The transmit end adds redundant error correction codes and the receive
end decodes and corrects errors to eliminate errors on the circuit.
Reduce the OSNR tolerance of the receiver. The reduced OSNR tolerance is called code gain.
The FEC capability varies directly with the code gain.
Classification of FEC Technology In-band FEC: supported by ITU-T G.707, code gain: 3 dB to 4 dB
Out-of-band FEC: supported by ITU-T G.975/709, code gain: 5 dB to 6 dB
Extremely robust FEC: no standard is available currently, highest code gain: 7 dB to 9 dB
Page52Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Optical Amplifiers
EDFA
RFA Raman Fiber Amplifier
Erbium Doped Fiber Amplifier
OA
Page53Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page54Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Structure of EDFA
Coupler
EDF
ISO
Pumping laser
ISO
PD
TAP
Signal input
TAP
Signal Output
PD
ISO: Isolator
PD: Photon Detector
Page55Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page56Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page57Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Main Performance Parameters of EDFA
Amplified spontaneous emission noise (ASE)
Noise figure (NF) = (S/N) in / (S/N) out ≥ 3 dB
Gain (G) = 10lg (Pout/Pin) (dB)
Gain flatness: gain balance
Bandwidth
Page58Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Raman Fiber Amplifier
Stimulated Raman Scattering
PumpGain
30nm
13THz
Pump3
70~100nm30nm
GainPump2Pump1
Page59Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page60Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Application of OA
Booster amplifier Line Amplifier Pre-amplifier
M40
OTU
OTU
M40
M40
OTU
OTU
M40
MUX
DMUX
OA OA OA
Page61Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Optical Multiplexer and Demultiplexer
Multiplexer
Fiber
Demultiplexer
Technologies of WDM/WDD
Diffraction grating technology
Medium film technology
Coupler technology
Arrayed waveguide technology
Main parameters of WDM/WDD
Insertion loss
Channel isolation
Channel bandwidth
Polarization dependent loss
Page62Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Diffraction Grating
Input light (1, 2... 8)
1
2
3
7
8
Grin lensgrating
Page63Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page64Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Coupler Multiplexer
IN OUT
12
34
56
。。。 .
。。。
1314
1516
Page65Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Arrayed Waveguide Grating
λ1,λ2… λn
Arrayed of waveguides 1…n
λ1
λnArrayed of fibers
Page66Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Interleaver
Divide a channel of signals with f frequency spacing
into two channels of signals with 2f frequency
spacing, and then the signals are output from two
channels.
It is applied in WDM/WDD that needs denser channel
spacing.
25/50GHz25/50GHz
50/100GHz50/100GHz
50/100GHz50/100GHz
Page67Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Optical Add/Drop Multiplexer (OADM)
OADM can be classified into two types:
FOADM: fixed OADM (arranged in series or parallel, or hybrid)
ROADM: reconfigurable OADM (further classified into
broadcast and select, or into demultiplexing and
switch/multiplexing)
OAMDOAMDOAMDOAMD
Page68Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Diversified Fixed Optical Add/Drop Multiplexer (FOADM)
Low costs
Simple structure
Maximum of 16 wavelengths
FOADM I
Multiple-layer dielectric film technologySerial OADMs
FOADM II
AWG technologyParallel OADMs
Supporting online upgrade
100% wavelength add/drop
EREG
Page69Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
ROADM: Broadcast and Select
Input signals are sent from the left side and divided into two channels of signals (broadcast) after passing through the demultiplexer.
The dropped channel is selected by a device such as a tunable filter and then the filter drops the selected channel of signals.
The straight-through channel passes through WB and is selected and filtered. This channel of signals and the add channel of signals are coupled and output.
Page70Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
ROADM: Demultiplexing/Switch/Multiplexing All input wavelengths are demultiplexed and cross-
connected to the proper output interfaces (drop or
straight-through) and then combined.
Page71Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Supervisory Technologies
OSC Optical Supervisory Channel Technology
ESC Electrical Supervisory Channel Technology
Page72Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
1510 nm / 1625 nm wavelengths1510 nm / 1625 nm wavelengths signal rate: 2.048 Mbit/ssignal rate: 2.048 Mbit/s receiver sensitivity: receiver sensitivity: – 48 dBm 48 dBm signal code: CMIsignal code: CMI transmitting power: 0 dBm to transmitting power: 0 dBm to –7 dBm7 dBm
1510 nm / 1625 nm wavelengths1510 nm / 1625 nm wavelengths signal rate: 2.048 Mbit/ssignal rate: 2.048 Mbit/s receiver sensitivity: receiver sensitivity: – 48 dBm 48 dBm signal code: CMIsignal code: CMI transmitting power: 0 dBm to transmitting power: 0 dBm to –7 dBm7 dBm
Page73Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page74Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Electrical Supervisory Channel
Features: Simple structure & cost saving Redundancy supported Improve power budget Reduce system complexity
M40
M40
OTU1OTU2OTU3OTU4
OTU1OTU2OTU3OTU4
SCC
SCC
Page75Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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?
Page76Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Optical source
Optical amplifier
Optical multiplexer
Supervisory technologies
Summary
Page77Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. WDM Overview
2. Transmission Media
3. Key Technologies
4. Master limitation of WDM system
5. Technical Specifications
Page78Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Restriction Factors of WDM
Optical power
dispersionOptical
signal-to-noise ratio
DHD JGDJ D J
WDM
Non-linear effect
Restriction factors
Page79Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Optical Power Budget
Fiber loss (dB) = P output (dBm) – P input (dBm) =
distance (km) x a (dB/km)
A. Loss coefficient
In the 1550 nm window, the loss coefficient of G.652 and
G.655 fibers is: a = 0.22 dB/km.
S R
P output P inputDistance L (km)
Station A Station B
Page80Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Power Topics
Optical amplifier technology
Reduction of system insertion loss
Page81Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Dispersion Chromatic dispersion (ps/nm) = distance (km) x
dispersion coefficient (ps/nm.km)
G.652 fiber: dispersion coefficient = 17 ps/nm.km
G.655 fiber: dispersion coefficient = 4.5 ps/nm.km
Chromatic dispersion is the main factor.
In long-haul transmission, the dispersion compensation
module (DCM) is adopted for dispersion compensation.
OMS
Distance L (km)
Station A Station B
Page82Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Dispersion Compensation Technology Dispersion compensation modes:
Optical domain dispersion compensation
Electrical dispersion compensation
Dispersion management soliton
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Optical Domain Dispersion Compensation To reduce the impact of the chromatic dispersion, adopt the DCM to compensate
for the accumulated dispersion on the fiber. Currently, the dispersion compensation fiber (DCF) in the DCM is used for dispersion compensation.
Dispersion slope compensation
Broadband dispersion compensation
PMD is generated randomly and is hard to be compensated.
Dispersion coefficient G.652
Common DCF
DSCF: dispersion slope compensation fiber
Wavelength
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OSNR
Distance (km)
Power
(dBm) Psignal
PASE
OSNR (dB)
Distance (km)
M40
M40
OA OA OA OAM40
D40
OA OA
OTU
OTU
OTU
OTU
OTS 1 OTS 2 OTS 3 OTS 4 OTS 5
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OSNR
Increase the system signal-to-noise ratio
Raman amplification technology
Pre-amplifier with low noise + booster amplifier with high
gain
Reduce the requirement on signal-to-noise ratio for the
system
New code modulation technology
Forward error correction (FEC) coding technology
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The OSNR requirement of different FEC and encoding modes
rate FEC mode Encding mode
OSNR requirement
remark
10Gbit/s
无 FEC NRZ 26
FEC NRZ 20
AFEC NRZ 18
AFEC CRZ 16
AFEC DRZ 14.5
AFEC ODB 16 CD tolerance is 4000ps/nm
10GE
AFEC NRZ 20 LBE(S)
AFEC CRZ 17.5
AFEC DRZ 17
AFEC ODB 19
40Gbit/sAFEC DRZ 16.5 LM40
AFEC ODB 17
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Non-Linear Technology
New code modulation technology
Dispersion management technology
Fiber-input power control
Channel spacing technology
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Contents
1. WDM Overview
2. Transmission Media
3. Key Technologies
4. Master limitation of WDM system
5. Technical Specifications
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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)
G.975 Forward error correction for submarine systems (FEC)
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Transmission Channel Reference Points
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Questions
Which are the ITU-T recommendations involved for
WDM part?
What is the absolute reference frequency for WDM
systems?
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