Training Course WDM Principle V1.0-20080902

www.huawei.com

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.


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. 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

OMU

ODU

OTU

OTU

OTU

OSC OSCOSC

LABA PA


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 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 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

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 according to the

following formula:

Fiber loss (dB) = fiber length (km) x fiber loss

coefficient (dB/km)


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.


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

different frequencies of the signal have different group

velocity and disperse from each other during propagation.

Characteristics of Fiber Dispersion


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)


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:

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


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.


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)


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 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.


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.


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


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.653 and G.655 fibers?

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

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


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


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…


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)


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 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


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

★★ ★★ ★★★ ★★★ ★★ ★


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 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


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


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


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

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 lensgrating


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

12

34

56

。。。 .

。。。

1314

1516


Arrayed Waveguide Grating

λ1,λ2… λn

Arrayed of waveguides 1…n

λ1

λnArrayed 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/WDD that needs denser channel

spacing.

25/50GHz25/50GHz

50/100GHz50/100GHz

50/100GHz50/100GHz


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)

OAMDOAMDOAMDOAMD


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


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 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


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




Restriction Factors of WDM

Optical power

dispersionOptical

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 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


Power Topics

Optical amplifier technology

Reduction of system insertion loss


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


Dispersion Compensation Technology Dispersion compensation modes:

Optical domain dispersion compensation

Electrical dispersion compensation

Dispersion management soliton


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)

M40

M40

OA OA OA OAM40

D40

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 requirement on signal-to-noise ratio for the

system


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/sAFEC DRZ 16.5 LM40

AFEC ODB 17


Non-Linear Technology


Dispersion management technology

Fiber-input power control

Channel spacing technology


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


Questions

Which are the ITU-T recommendations involved for

WDM part?

What is the absolute reference frequency for WDM

systems?

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Documents

Training Course WDM Principle V1.0-20080902