Principles_of_WDM__1674788675.pdf

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

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page2
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 differenttypes 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. Master Limitation of DWDM system
5. 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/ODU)
 Optical Amplifier (OA)
 Supervisory Channel (OSC/ESC)
System Structure
OTU
OTU
OTU
O
M
U
O
D
U
OTU
OTU
OTU
OSC OSC
OSC
LA
BA PA

Transmission Modes
⚫ Single fiber unidirectional transmission
M
4
0
M
4
0
MUX DMUX
O
T
U
O
T
U

M
4
0
M
4
0
MUX/DMUX DMUX/MUX
Transmission Modes
⚫ Single fiber bidirectional transmission
O
T
U
O
T
U

Application Modes
⚫ Open System
M
4
0
M
4
0
MUX DMUX
O
T
U
O
T
U
Client Client

Application Modes
⚫ Integrated System
M
4
0
M
4
0
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 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

Distribution of Optical Wavelength Areas
⚫ Nominal central frequency refersto the central wavelength
correspondingto 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
⚫ 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
4. Master limitation of DWDM system

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

Characteristics of Fiber
⚫ Loss
⚫ Dispersion
⚫ Non-linear

Characteristics of Fiber Loss
⚫ Fiber loss is classified into:
 Absorption loss
 Scattering loss
 Bending loss
⚫ The fiber loss can be calculated accordingto the following
formula:
 Fiber loss (dB) = fiber length (km) x fiber loss coefficient (dB/km)

Attenuation
900 1300 1400 1500 1600 1700
nm
dB/km
2
3
1
4
5
1200
Multi-mode
（
850~900nm
）
O
band
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.

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.

⚫ 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 differentfrequenciesof the
signal have differentgroup velocity and dispersefrom each other during
propagation.
Characteristics of Fiber Dispersion

Chromatic Dispersion
⚫ Chromaticdispersion:
 pulse broadening,cause intersymbol interference
⚫ The chromatic dispersion can be calculated accordingto the
following formula:
 CD (ps/nm) = fiber length (km) x CD coefficient(ps/km.nm)
Time
Power
Optical pulses
Transmitting
L1 (km)
Transmitting
L2 (km)

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.

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:
Type Definition Scope Main Specifications
G.652
The standard single-mode fiber
(SMF) refers to the fiber whose
zero-dispersionpoint (the zero-
dispersionwavelength) 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 is0.35 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-dispersionwavelengthis
1300–1324 nm. The dispersioncoefficientof the 1550 nm band is
positive and the typical value of the dispersioncoefficientD is 17
ps/(nm.km). The maximum value is not more than 20 ps/(nm.km).
G.653
Dispersion-shiftedfiber(DSF) refers
to the fiberwhose 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 lessthan
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 coefficientis3.5
ps/(nm.km). The dispersioncoefficientin the DSF is too small or may
be 0 for 1550 nm bands, especiallyC band.
G.655
Non-zero dispersion-shiftedfiber
(NZDSF) refers to the fiberwhose
zero-dispersionpoint is shiftedaway
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
specifiedin 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 dispersioncoefficientof the
G.655 NZDSF varies with vendors and needs to be confirmed based
on actual situations, usually4.5 ps/(nm.km) and 6 ps/(nm.km).
G.652/G.653/G.655Single-Mode Optical Fibers

Dispersion
coefficient
G.655
1550nm
1310nm
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.

Non-Linear Effects of Single-Mode Optical Fibers
⚫ Fiber Non-linear effects can be classified into:
 Stimulated non-flexible scattering: stimulated Raman scattering (SRS) and
stimulated Brillouin scattering (SBS)
 Kerr-effect: self-phase modulation (SPM), cross-phase modulation (XPM)
and four wave mixing (FWM)

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

SBS
• A non-linear phenomenon causing the strong forward
transmission signal converted to backwardtransmission 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.

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.

FWM
Definition: 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
f
f3 f2
f1
f
f3 f2
fFWM
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

Note!
⚫ Non-linear effects cannot be eliminated or compensated for. So
they should be restricted as much as possible!

Questions
⚫ What’s difference between the refractive index of the cladding
and core?
⚫ What are the features of G.652,G.653and G.655fibers?
⚫ What problems may occur when optical signals are transmitted in
single-mode fibers?

⚫ Structure of optical fiber
⚫ Types of optical fiber
⚫ Characteristics of optical fiber
Summary

Contents
1. WDM Overview
3. Key Technologies
4. Master limitation of WDM system

WDM System Key Technologies
⚫ Optical
Source/receiver
⚫ Optical Amplifier ⚫ Supervisory
Technologies/code
technology
Key Tech. in WDM
⚫ Optical Multiplexer
and Demultiplexer

Requirements of Optical Source
1 Larger dispersion tolerance value
2 Standard and stable wavelength

Direct modulator

Electro-Absorption (EA) external modulator

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

Wavelength Tunable Technology
⚫ Wavelength Tunable Principle
 The wavelengths correspondingto 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.
⚫ Advantagesof Wavelength Tunable Technology
 Reduction of spare parts stock
 Flexible networking

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 appearanceis 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…

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)
Opticallypumped MEMs-VCSEL (Coretek)
MEMs-DFB array (Santur)

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……

Comparison of coding technologies with 10 Gbit/s rate
Coding Technology Advantage Disadvantage Application
NRZ
⚫Narrow spectral width
⚫Simple structure of modulation
and demodulation
⚫Low cost
⚫Low ability to prevent non-
linear effects
⚫High OSNR tolerance
⚫Low dispersiontolerance
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 effects
⚫Lower OSNR tolerance than that
of NRZ
⚫Wide spectrum bandwidth
⚫Does not support 25 GHz system
⚫Low dispersiontolerance
⚫Does not support wavelength
adjustable
10 Gbit/s and to long-
SuperDRZ
⚫Narrow spectrum bandwidth
⚫Supports 25 GHz system
⚫High dispersiontolerance
linear effects
⚫Supports wavelength adjustable
⚫Cost effective
10 Gbit/s and to long-
ODB
⚫High dispersiontolerance
linear effects
⚫Supports wavelength adjustable
If the optical power of signals that
are just transmittedinto the optical
fiber is great, the transmission
distance decreases because of
dispersionlimited. The ODB is
not applied to long-distance
transmission.
Applied to 10 Gbit/s
metropolitanareanetwork

Comparison of coding technologies with 40 Gbit/s rate
COMPAREITEM NRZ ODB DRZ（HW) NRZ-DPSK RZ-DQPSK DP-QPSK
OSNR ★ ★ ★★ ★★★ ★★★ ★★★★
CD tolerance ★★ ★★★ ★★ ★★ ★★★ ★★ ★★
PMD tolerance ★ ★★ ★★ ★★ ★★★ ★★ ★★
$$ ★★★★ ★★★★ ★★★ ★★ ★★ ★
50GHz × √ × × √ √
Non-linear
tolerance
★★ ★★ ★★★ ★★★ ★★ ★

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

FEC Technology
⚫ Forward Error Correction Technology
 The transmit end adds redundanterror 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 robustFEC: no standard is availablecurrently, highest code gain: 7 dB to 9
dB

Optical Amplifiers
EDFA
RFA Raman Fiber Amplifier
Erbium Doped Fiber Amplifier
OA

Stimulated radiation
⚫ Er3+ energy level diagram
Erbium Doped Fiber Amplifier
E2 meta-stable state
E3 excited state
E1 ground state
1550nm
signal light
1550nm
signal light
980nm
pump light
Decay

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-flatness
 Optical surge problem
…
Advantages Disadvantages

Automatic Gain Control
Pin Pout
Gain
λ1~ λn
λ1~ λn
Gain no change!
EDFA
PIN
pump
PIN
DSP
splitter splitter
EDF
Input Power: Pin Output Power: Pout
Gain = Pout / Pin is invariable
coupler

Main Performance Parameters of EDFA
⚫ Amplified spontaneousemission noise (ASE)
⚫ Noise figure (NF) = (S/N) in / (S/N) out ≥ 3 dB
⚫ Gain (G) = 10lg (Pout/Pin) (dB)
⚫ Gain flatness: gain balance
⚫ Bandwidth

Raman Fiber Amplifier
⚫ Stimulated Raman Scattering
Pump
Gain
30nm
13THz
Pump3
70~100nm
30nm
Gain
Pump2
Pump1

Features of Raman
 Flexible gain wavelength
 Simple structure
 Nonlinear effect can be reduced;
 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
M
4
0
OTU
OTU
M
4
0
M
4
0
OTU
OTU
M
4
0
M
U
X
D
M
U
X
OA OA OA

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

Diffraction Grating
Input light (1, 2... 8)
1
2
3
7
8
Grin lens
grating

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

Coupler Multiplexer
IN OUT
1
2
3
4
5
6
。
。
。.
。
。
。
13
14
15
16

Arrayed Waveguide Grating
λ1,λ2… λn
Arrayed of waveguides 1…n
λ1
λn
Arrayed of fibers

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/WDDthat needs denser channel spacing.
25/50GHz
50/100GHz
50/100GHz

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)
OAMD

Diversified Fixed Optical Add/Drop Multiplexer (FOADM)
⚫ Low costs
⚫ Simple structure
⚫ Maximum of 16 wavelengths
❖ FOADM I
Multiple-layer dielectric
film technology
Serial OADMs
❖ FOADM II
AWG technology
Parallel OADMs
⚫ Supporting online upgrade
⚫ 100% wavelength add/drop
EREG

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.

ROADM: Demultiplexing/Switch/Multiplexing
⚫ All input wavelengths are demultiplexed and cross-connected to
the proper output interfaces (drop or straight-through)and then
combined.

Supervisory Technologies
OSC Optical Supervisory Channel Technology
ESC Electrical Supervisory Channel Technology

Optical Supervisory Channel
⚫ Requirements:
 Operating wavelength should be differentfrom the pumping
wavelength of OA.
 Operating wavelength should not take 1310nm window.
 Available when OA fails;
 Suitable for long distance transmission.
M
4
0
M
4
0
F
I
U
OTU1
OTU2
OTU3
OTU4
OTU1
OTU2
OTU3
OTU4
F
I
U
OSC OSC
S
C
C
S
C
C
1510 nm / 1625 nm wavelengths
signal rate: 2.048 Mbit/s
receiver sensitivity: – 48 dBm
signal code: CMI
transmitting power: 0 dBm to –7 dBm

Typical frame structure of OSC
TS0 FA TS17 F2 byte
TS1 E1 byte TS18 F3 byte
TS2 F1 byte TS19 E2 byte
TS14 ALC byte Others Reserved
TS3-TS13, TS15 D1-D12 bytes
TS0 TS1 TS2 TS3 …… TS14 TS15 TS16 …… TS31

Electrical Supervisory Channel
⚫ Features:
 Simple structure& cost saving
 Redundancy supported
 Improvepower budget
 Reduce system complexity
M
4
0
M
4
0
OTU1
OTU2
OTU3
OTU4
OTU1
OTU2
OTU3
OTU4
S
C
C
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?

⚫ Optical source
⚫ Optical amplifier
⚫ Optical multiplexer
⚫ Supervisory technologies
Summary

Contents
1. WDM Overview
3. Key Technologies
4. Master limitationof WDM system

Restriction Factors of WDM
Optical
power
dispersion
Optical
signal-to-
noise ratio
DHD JGDJ
D J
WDM
Non-linear
effect
Restriction factors

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 coefficientof G.652 and G.655 fibers is: a
= 0.22 dB/km.
S R
P output P input
Distance L (km)
Station A Station B

Power Topics
⚫ Optical amplifier technology
⚫ Reduction of system insertion loss

Dispersion
⚫ Chromaticdispersion (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
⚫ Chromaticdispersion 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

Dispersion Compensation Technology
⚫ Dispersion compensation modes:
 Optical domain dispersion compensation
 Electrical dispersion compensation
 Dispersion managementsoliton

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

OSNR
Distance
(km)
Power
(dBm) Psignal
PASE
OSNR
(dB)
Distance
(km)
M
4
0
M
4
0
OA OA OA OA
M
4
0
D
4
0
OA OA
OTU
OTU
OTU
OTU
OTS 1 OTS 2 OTS 3 OTS 4 OTS 5

OSNR
⚫ Increase the system signal-to-noise ratio
 Raman amplification technology
 Pre-amplifier with low noise + booster amplifier with high gain
⚫ Reduce the requirementon signal-to-noise ratio for the system
 New code modulation technology
 Forward error correction (FEC) coding technology

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/s
AFEC DRZ 16.5 LM40
AFEC ODB 17

Non-Linear Technology
⚫ New code modulation technology
⚫ Dispersion managementtechnology
⚫ Fiber-input power control
⚫ Channel spacing technology

Contents
1. WDM Overview
3. Key Technologies
4. Master limitation of WDM system
5. TechnicalSpecifications

Related ITU-T recommendations
⚫ G.652 Characteristics of a single-modeoptical 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 transportnetwork (OTN)
⚫ G.975 Forward error correction for submarinesystems(FEC)

Transmission Channel Reference Points

Questions
⚫ Which are the ITU-T recommendations involved for WDM part?
⚫ What is the absolute reference frequency for WDM systems?

Principles_of_WDM__1674788675.pdf

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