WDM network Technology training

Optical Network Curriculum

Development Section

Optical Network Curriculum

Development Section

ISSUEISSUE

WDM Network TechnologyWDM Network Technology

1.01.0

ObjectivesObjectives

Understand the basic concept of WDM

network ,

Grasp the budgeting method in WDM

network design ,

Know channel coding technology in WDM

network ,

On completion of this course ,you will be able to :

ContentsContents

Chapter 1 WDM network description

Chapter 2 Factors to be considered in

WDM networking budget

Chapter 3 Coding Technology

Chapter 1 WDM network descriptionChapter 1 WDM network description

1.1 WDM NE Types

1.2 WDM Network Topology1.2 WDM Network Topology

OTM

OTM

1.OTM

OADM2.OADM

3.OLA

4.REG

REG

REG

WDM NE TypesWDM NE Types

OTMOTM

OTU DeMUX

OTUMUX

Optical Amplifier

Optical Amplifier

OSC

OLAOLA

Optical amplifier

OSC

Optical amplifier

OADMOADM

OTU

OADM

OSC

OA

OA

TMUX

OA

OA

REGREG

DeMUXMUX

Optical amplifier

OSC

OTU

DeMUX MUXOptical amplifier

OTU

Chapter 1 WDM network descriptionChapter 1 WDM network description

1.1 WDM NE Types1.1 WDM NE Types

1.2 WDM network topology

Point to Point NetworkPoint to Point Network

SDHOTM OLA OLA OTM SDH

It consists of OTM and OLA ,and OADM is

not included .

Chain networkChain network

STM-1616个

OTM

STM-1616个

STM-168个

OTM OADM

Ring NetworkRing Network

OADM

OADM OADM

OADM

Note: OADM is including static OADM and back-to-back OTM (OTM-OTM)

Chapter 1 WDM network descriptionChapter 1 WDM network description

1.1 WDM NE Types1.1 WDM NE Types

1.2 WDM network Topology1.2 WDM network Topology

ContentsContents

Chapter 1 WDM network description

Chapter 2 Factors to be considered in

WDM networking budget

Chapter 3 Coding Technology

Chapter 2 Factors to be considered in WDM networking budget

Chapter 2 Factors to be considered in WDM networking budget

2.1 Attenuation

2.2 Dispersion

2.3 OSNR

2.4 Nonlinearity

AttenuationAttenuationAttenuationAttenuation

Under worst condition :L=(Ps-Pr)/a

Ps :Launched optical power (with single channel) at transmitter side Pr :Receiving optical power (with single channel) at receiver side .a :Attenuation coefficient . it is recommended as 0.275dB/km (for G.652) from ITU-T when taking optical splicing and redundancy into consideration ,

A BS R

LPs Pr

AttenuationAttenuationAttenuationAttenuation

Example ：

Ps=5dBm, Pr= -17dBm, L=

Ps=5dBm, Pr= -28dBm, L=

80km

120km

Chapter 2 Factors to be considered in WDM networking budget

Chapter 2 Factors to be considered in WDM networking budget

2.1 Attenuation

2.2 Dispersion

2.3 OSNR

2.4 Nonlinearity

DispersionDispersion

Dispersion limited distance=

(Dispersion tolerance/dispersion coefficient)- (10～ 30)

(Normally , Redundancy is considered as 10~30 km

)

Dispersion tolerance ： it depends on the spectrum perfo

rmance of light source .

Dispersion performance with STM-16 level Dispersion performance with STM-16 level

Dispersion tolerance of light source is 7200ps/nm ,

12800ps/nm etc,.

Dispersion coefficient is about 17ps/nm.km in G.652

fiber (20ps/nm is used in project when redundancy is

considered),

Typically ,dispersion coefficient is about 1~6ps/nm.km

in G.655 fiber .

Dispersion performance with STM-64 level Dispersion performance with STM-64 level

Dispersion tolerance of light source is 700ps/nm , 1200p

s/nm etc,.

Dispersion coefficient is the same as above .

Max. transmission distance without compensation :

In G.652 L=700/17-(10～ 30)

In G.655 L=700/6-(10～ 30)

10G10GLA LABA PA

100km100km 100km

DCF:60km DCF:80km DCF:80km DCF:60km

Distributing compensation is recommended to obtain good effect .Distributing compensation is recommended to obtain good effect .

Dispersion compensationDispersion compensationDispersion compensationDispersion compensation

It is necessary to make dispersion compensation in STM-64 system .

Chapter 2 Factors to be considered in WDM networking budget

Chapter 2 Factors to be considered in WDM networking budget

2.1 Attenuation

2.2 Dispersion

2.3 OSNR

2.4 Nonlinearity

NoiseNoise （（ ASEASE））

Signal Signal

ASE NoiseASE Noise

OSNR

Span

OSNR is used to measure accumulation degree of ASE noise .defined as :

The ratio of signal power to the noise power inside a specific band nearby signal:

OSNROSNR

ASE

sP

POSNR

Adopt Optical Amplifiers with low noi

se :

•Application of Preamplifiers with low no

ise

•Raman technology

How To Reduce Noise AccumulationHow To Reduce Noise Accumulation

System Design With Raman AmplifiersSystem Design With Raman AmplifiersSystem Design With Raman AmplifiersSystem Design With Raman Amplifiers

Chapter 2 Factors to be considered in WDM networking budget

Chapter 2 Factors to be considered in WDM networking budget

2.1 Attenuation

2.2 Dispersion

2.3 OSNR

2.4 Nonlinearity

Nonlinearity LimitationNonlinearity Limitation

Nonlinearity Limitation :

Limit optical power of single channel

Limit optical power coupled into fiber

Refer to G.663

Take FWM into account ,channel spacing is

strictly required in G.653 .

Refer to G.692

Nonlinearity :

SBS, SRS, FWM, SPM, XPM etc,.

ContentsContents

Chapter 1 WDM network description

Chapter 2 Factors to be considered in

WDM networking budget

Chapter 3 Coding Technology

How to increase OSNR tolerance in WDM system?How to increase OSNR tolerance in WDM system?

Adopt Forward Error Correction Technology： FE

C/EFEC

Adopt special coding technology : RZ format etc,.

Chapter 3 Coding TechnologyChapter 3 Coding Technology

Chapter 3 Coding TechnologyChapter 3 Coding Technology

3.1 FEC coding

3.2 RZ coding3.2 RZ coding

FEC TechnologyFEC Technology

FEC（ Forward Error correction） At transmitter end, some additional overheads bits or by

tes are inserted into the transmitting data, at receiver en

d, wrong data (error) will be corrected through addition

al bits or bytes.

With FEC function, It can improve BER performance wit

hout increasing OSNR requirement.

FEC TechnologyFEC Technology

•Digital encapsulation

•RS Coding （ 255 ， 239 ）

FEC is used to correct code, it doesn’t increase optical power or improve OSNR, but data error ratio is reduced under the same condition. In case of BER<10-12

Without FEC :OSNR is required to be more than 20dB

With FEC, OSNR is required to be more than 16dB

In practical application, when FEC function is available, it means long distance transmission with multiple sections can be achieved.

OSNR and FECOSNR and FEC

Chapter 3 Coding TechnologyChapter 3 Coding Technology

3.1 FEC coding

3.2 RZ coding3.2 RZ coding

R ZR Z

RZ － Return to Zero Code

NRZ

RZ

1 1 11 11 1 00

CLOCK

T

T

T

RZ CodingRZ Coding

I1-I0

I1-I0

• Small duty cycle and power density；

• Higher ability to resist dispersion and nonlinearity,

• Higher ability to resist eye pattern degradation resulted by PMD.

Super WDMSuper WDM