01-wdm principle issue1.21

7/28/2019 01-Wdm Principle Issue1.21

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WDM Principle

ISSUE 1.21



HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 1

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?




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.




Chapter 1 WDM Overview

Chapter 2 WDM Transmission Media

Chapter 3 WDM Key Technologies

Chapter 4 Technology Specifications for

WDM System




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




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




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




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




Transmission modes – Unidirectional transmission

MUX DMUX

Single fiber unidirectional transmission

O

T

U

O

T

U

STATION A STATION B




Transmission modes - Bi-directional transmission

Single fiber bi-directional transmission

STATION A STATION B

MUX/DMUX DMUX/MUX

O

T

U

O

T

U




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




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




Advantages of DWDM

Transparent media

Long haul transmission

High capacity

Use existing optical fibers

High performance-to-cost ratio

Reliability

Easy upgrading




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




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.




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.







Chapter 4 Technology Specifications for

WDM System




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.




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




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




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




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.




Summary

In this chapter, we have learned :

The basic structures and types of

optical fibers;

The characteristics of optical fibers.







Chapter 4 Technology Specifications for WDM System




Optical Source Optical Supervisory

Technologies

WDM System Key Technologies

Optical Amplifiers Multiplexer andDemultiplexer




1) Larger dispersion tolerance value;

2）Standard and stable wavelength.

Requirements of Optical Source




Laser

Direct modulation

Electro-absorption (EA) external modulator

Mach-Zehnder (M-Z) external modulator




Direct modulation

Output laser is controlled by input current

Transmission rate≤2.5Gb/s

Transmission distance≤100km

modulation

current




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




LD

Mach-Zehnder (M-Z) external modulator

Long dispersion limited distance

High cost

Negligible chirp

High dispersion tolerance

modulationcurrent




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




Raman Fiber Amplifier (RFA)

Erbium Doped Fiber Amplifier (EDFA)

Semiconductor Optical

Amplifier (SOA)

Optical Amplifiers




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




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




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.




Cascading amplification of amplifier gain unflatness

Cascading amplification of amplifier gain flatness

Impact of Gain Flatness in Long Haul Transmission




>1dB

<0.5dB

Drop

Gain Locking




>1dB

<0.5dB

Add

Gain Locking




The Operating Theory of Raman Fiber Amplifier

Stimulated Raman Scattering

(SRS)

Pump

Gain

30nm

13THz (~100nm)




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




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.




Application of OA

According to its application:

BA: Booster amplifier

LA: Line amplifier

PA: Pre-amplifier




n

n

n

n

n

n

Multilpexer Demultiplexer

Multiplexer and De-multiplexer




Optical Grating Type DWDM Component

Periodic variation of the refractive index (grating)

Ultraviolet light interference

¦ Ë1¦ Ë2¦ Ë3 ¦ Ë2




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




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




1）Optical Supervisory Technologies（OSC）

2）Electrical Supervisory Technologies（ESC）

Optical Supervisory Technologies




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




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




OSC transmission

O

M

B

A

P

A

O

D

OSC input OSC output

F

IU

F

IU




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




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?




Summary

In this chapter, we have learned:

Optical source;

Optical amplifier;

Wavelength division Multiplexer;

Optical supervisory channel.






Chapter 3 DWDM Key Technologies

Chapter 4 Technology Specifications for WDM System




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)




Definition of Transmission Channel Reference Points




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.




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?




Summary

In this chapter, we have learned:

Related ITU-T recommendations

Distribution of Optical Wavelength

Areas



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01-wdm principle issue1.21

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