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WDM Technology overview

Do not delete this graphic elements in here:

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WDM Technology overview

Do not delete this graphic elements in here:

By the end of the course, you will be able to: • Explain the main optical transmission concepts. • Describe the main impairments occurring within a fiber.

• Quote the 5 laser classes according to their risks. • Explain the main WDM concepts. • Describe the penalties due to wavelength multiplexing. • Describe the architecture of WDM networks. Proprietary - Use pursuant to Company instructions -All Rights Reserved © Alcatel-Lucent 2011

Course outline WDM Technology

1

Optical Transmission Basics You will learn in this chapter … … what the main optical transmission concepts are … what the optical link devices are

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Transmission Principle

0 1 0 1 1

1 1 0 1 0

Optical fiber

Parts of a Transmission Link

Input

Output

TRANSMITTER

RECEIVER

Electrical Interface

Electrical Interface

Data Encoder Modulator Light Emitter

Optical fiber

Data Decoder Demodulator Light Detector

Transmitter: Overview Input(s)

TRANSMITTER Electrical Interface • Video • Audio • Data

Data Encoder/Modulator • AM • FM • Digital

Light Emitter • LED: 780nm, 850nm, 1300nm • LD: 850nm, 1310nm, 1550nm, 1625nm

Transmitter: Analog to Digital Conversion

A In

A Out

A/D Converter

D/A Converter

TDM

Optical TX

Optical fiber

Optical RX

TDDM

Pulse Code Modulation (PCM) Anaput

Digital Output A/D

Transmitter: Digital to Optical Conversion Digital signal

1 0 1 1

Laser

External Modulator

1 0 1 1

Fiber

Transmitter: Light Emitter Parameters Wavelength range (nm) Ultraviolet

Visible

Infrared

X-rays, Gamma rays

Radio waves, Long waves

Fourth window

Third window

900 1000 1100 1200 1300 1400 1500 1600 1700

Second window

800

First window

700

Launch power (dBm) Maximum power

Minimum power

P(mW) P(dBm) = 10 · Log 10(-------) 1 mW

nm

Receiver: Overview Output(s)

RECEIVER Electrical Interface • Video • Audio • Data

Data Decoder/Demodulator • AM • FM • Digital

Light Detector • PIN Diode • APD • Materials: Si, Ge, In, GaAs

Receiver: Light Detector Parameters

PIN photodiode Fiber Cladding Fiber Core

Metal (-)

Anti-reflection Coating

Received power (dBm) Maximum power

P + Region Intrinsic Region

(saturation)

Hole Electron

Electron - Hole N + Region Metal (+)

Minimum power (sensitivity)

Optical Interface Classification

Optical network application

Wavelength range

TRANSMITTER

S–1.1 RECEIVER

Digital signal bit rate

Optical Fiber: Overview

Jacket Buffer Cladding Core

Optical Fiber: Light Guiding Principle

Refraction

n1 Critical cone

Reflection

θcritical n2>n1

n2 n1

Laser

sin Θcritical = n1/n2

with

n = c/v

Optical Fiber: Types Type

Refractive index n2

n1

Core/Cladding (diameter)

n(r)

62.5m/125m

n(r)

50m/125m

n(r)

9m/125m

Multimode, Step-index

Multimode, Graded-index

Single-mode

2

Optical Transmission Impairments You will learn in this chapter … … what the main optical impairments are … how they can be compensated

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Attenuation: Intrinsic Factors

Scattering

Absorption

Attenuation: Total Attenuation Curve Optical loss (dB/km)

4

3

Third window

First window

Second window

5

Total attenuation curve

2

Intrinsic absorption

Intrinsic scattering (Rayleigh scattering)

1

0 700

800

900

1000

1100

1200

1300 1400

1500

1600 1700

1800

1900

2000

Wavelength (nm)

Attenuation: Total Attenuation Curve [cont.] Optical loss (dB/km)

3

Third window

First window

4

Total attenuation curve

2

1

Second window

5

Intrinsic absorption

Intrinsic scattering (Rayleigh scattering)

0 700

800

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Wavelength (nm)

Optical loss (dB/km) 0.30 0.28

1460nm

0.26 0.24

1550nm

0.22 0.20

S

0.18

1450

1500

C 1550

L 1600

Wavelength (nm)

Attenuation: Calculation

P

P Optical fiber

Pi

Pi



Attenuation ()

L

Po = Pi – ( x L) Where:  Po (dBm): output power  Pi (dBm): input power  L (km): length of the fiber   (dB/km): attenuation of the fiber

Po Po 

Dispersion Types 

Dispersion is the spreading of light pulses as they travel down an optical fiber. Optical fiber Pi

Po

Time



Two general types of dispersion affect optical systems:  Chromatic Dispersion (CD),  Polarization Mode Dispersion (PMD).

Time

Chromatic Dispersion: Definition

Pi

Optical fiber

Po

Time

Time

Optical fiber Pi Time

Po Positive chromatic dispersion

Time

Chromatic Dispersion: Standard Single-Mode Fiber (SSMF)

Dispersion (ps/nm/km) 25 20 15 10 5 0

-5

Wavelength (nm)

-10 1250 1300 1350 1400 1450 1500 1550 1600 1650

Chromatic Dispersion: Calculation

P

P Optical fiber

Pi

Pi

0.6 Pi T 2

Chromatic dispersion (D)

L

T = D x L x  Where:  T: pulse widening  D (ps/nm/km): chromatic dispersion  L (km): length of the fiber   (nm): spectral width of the signal

Po Po T T

Polarization Mode Dispersion

• Different polarization states

Fiber

Input Signal

of light travel at slightly different speeds throughout the fiber Output Signal

pulse enough to make it overlap with other pulses or change its own shape enough to make it undetectable at the receiver

Ideal

fast

• This effect can spread the

• DGD is the fundamental

Normal

measure of PMD and is measured in picoseconds (10-12 seconds) slow

delay = DGD (Differential Group Delay)

• PMD can be a problem at 10Gbit/s or 40Gbit/s transmission rates

Polarization Mode Dispersion PMD is caused by the asymmetry of the fiber-optic strand : Intrinsic • Manufacturing process • Mechanical stress stress geometry - Installation - Heating and Cooling - Vibration

Extrinsic

stress

Random Effects => Fiber has a distribution of DGD values over

time. As an approximation, the maximum instantaneous DGD is about 3.2 times the average DGD (=PMD) of a fiber.

bend

twist

Polarization Mode Dispersion PMD coefficients are in units of ps/(√ of km). Some fibers installed before the mid 1990’s have coefficients of about 1–2ps/(√ of km). DGD of this magnitude, in an OC– 192/STM–64 transmission system, can be expected to result in a bit-error rate that is severe enough to cause service problems. Solution to PMD:

•Use PMDC (Not enough mature - Not use in the field) •Design link with additional OSNR margins for PMD •Reduce link length or use intermediate O-E-O Regeneration •Deploy New fiber with better PMD coefficient

Nonlinear Effects



Nonlinear effects tend to manifest themselves when optical power is very high. They become important in WDM systems.



The most important types of nonlinear effects are:     

Stimulated Brillouin Scattering (SBS) Stimulated Raman Scattering (SRS) Four-Wave Mixing (FWM) Self-Phase Modulation (SPM) Cross-Phase Modulation (XPM)

Transmission Improvement: Optimized Fibers



To improve the transmission quality, the first step is to select the appropriate fiber.



There are three basic classes of single-mode fiber:  Non-Dispersion-Shifted Fiber (NDSF), G.652:  Standard Single-Mode Fiber (SMF or SSMF).  The dispersion zero point is near 1310nm.

 Dispersion-Shifted Fiber (DSF), G.653:  The dispersion zero point is around 1550nm.

 Non-Zero Dispersion-Shifted Fiber (NZDSF), G.655:  The dispersion zero point is around another wavelength.

Transmission Improvement: Optimized Fibers [cont.]

Dispersion (ps/nm/km) EDFA

20 15 10

Non DSF

5 0

(-D) NZDSF (+D) NZDSF

-5 -10

DSF

Wavelength (nm)

-15 1250 1300 1350 1400 1450 1500 1550 1600 1650

Optimized Fibers – Overview for repeatered links < 700 km

For repeatered links < 700km only!

SSMF / G.652

DSF / G.653

NZ-DSF / G.655

DWDM C Band

Good

Bad

Excellent

DWDM L band

Good

Good

Mean

TDM

Mean

Excellent

Good

Transmission Improvement: Modulation Format 

Different coding types are available for the transmitter to optimize the signal transmission. These types include:

 Non-Return-to-Zero (NRZ) 1

1

0

1

1

0

1

Full Half Zero

0

 Return-to-Zero (RZ) 1

 Optical Duobinary

 Carrier-Suppressed Return-to-Zero (CSRZ) 0

0

0

π

Transmission Improvement: Amplification & Regeneration

Signal (u.a.)

attenuation

0,8

1,0 0,8

1R

0,6 0,4

0,6 0,4

0,2

0,2

0,0 -0,2

Amplitude Noise

Signal (u.a.)

Re-amplifying

1,0

0,0 0,0

0,2

0,4

0,6

0,8

1,0

1,2

-0,2

0,0

Time (bit period)

0,2

0,4

0,6

0,8

1,0

1,2

Time (bit period)

Re-shaping

2R

Jitter reduction

Jitter

Signal (u.a.)

1,0

Noise Reduction

0,8

0,6

3R

0,4 0,2

0,6 0,4 0,2

0,0 -0,2

Signal (u.a.)

1,0

0,8

0,0

0,2

0,4

0,6

0,8

Time (bit period)

1,0

1,2

Re-timing

0,0 -0,2

0,0

0,2

0,4

0,6

0,8

1,0

Time (bit period)

1,2

Optical Amplification

OPTICAL AMPLIFIER Signal in

Pump coupler

Signal out Active fiber doped with Erbium ions

Excited state

Pump laser diode

Ground state

electron

Energy supply (pumping)

photon

Spontaneous emission

Noise generation

Signal in

Stimulated emission

Optical amplification

Optical Amplification [cont.] 

Optical amplifier key performance parameters:    

Output power Gain Gain flatness Noise level

Output power

Conventional Band

Standard EDFA response spectrum  1525nm

1565nm

Transmission Improvement: Dispersion Compensation Fiber

λoper

D (ps/nm/km)

D (ps/nm/km)

λoper  (nm)

"Standard fiber", (+D) NZDSF

λoper

λoper  (nm)

Dispersion compensation fiber, (-D) NZDSF

3

Optical Safety You will learn in this chapter … … what the laser risks are … how to protect an operator

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Radiation Absorption

EYE absorption of electromagnetic radiations

Retina

Visible and close to infrared

Very hazardous Focused on retina

Laser Classification 

The International Electrotechnical Commission IEC825:  Gives the safety recommendations.  Grades laser in 5 classes according to their risk. Power (mW) 1000

Class 4

100 10

Class 3B Class 3A

1 0.1

Class 2

0.01

Class 1

0.001

400

600

Wavelength (nm) 800

1000

1200

1400

1600

Laser Classification [cont.]  Telecom laser domain

Class

1 1550nm

1300nm 850nm

3A

3B

4

10

17

27

dBm

(10)

(50)

(500)

(mW)

9.5

15

27

dBm

(10)

(32)

(500)

(mW)

-4

+2.5

27

dBm

(0.4)

(2)

(500)

(mW)

Laser Risks

Class 1

No hazard if used in normal conditions*.

Class 2

Only concerns the band ranging from 400 to 700nm.

* If you do not look directly and closely at the laser beam.

Class 3A

No hazard if used in normal conditions, except if you use optical appliances (binoculars, microscope, monocular, etc.).

Class 3B

Hazard if you look directly at the laser beam.

Class 4

Hazard for eye and skin, fire risk.

Safety Instructions Precautions to be taken in class 3A … Hazard in class 3B & 4 … : So you need to quantify and locate the corresponding power.

INSTRUCTIONS The optical interfaces peculiar to powers 3A, 3B and 4 are identified by the following symbol:

BASIC PRINCIPLES Do not observe a connector or a fiber in its longitudinal axis. Do not observe a connector or a fiber unless you are at a distance of 10 cm or more. Place systematically the protective caps on a free connector.

LASER RADIATION: DO NOT LOOK INSIDE THE BEAM CLASS-3A LASER RADIATION UNIT

Automatic Safety Mechanism: Automatic Laser Shutdown (ALS)

Network Element n°1

Network Element n°2

Optical interface

Optical interface Cut-off

ALS command

Power Shutdown 2

LOS 2

LOS 1 Power Shutdown 1

ALS command

Automatic Safety Mechanism: Laser Restart Management Automatic laser shutdown

Start

Yes

Section in normal operation ALS in service

Automatic Restart

Signal received from remote end?

Timeout (60-300)s

Manual restart

Manual restart for testing

Laser in operation for (2  0.25) s

Laser in operation for (90  10) s

No No

Loss of transmitted signal for t >= (550  50) ms? Yes

Laser in operation for (2  0.25) s

4

WDM Transmission Basics You will learn in this chapter … … what the main WDM concepts are … what the WDM components are

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Time Division Multiplexing: Concept

Bits of information

Transmission link

TDM

Time Division Multiplexing: SDH Example

Bit rate = 2.5Gbps

Link rate = (2.5Gbps x 4 = 10Gbps) Incoming streams

Outgoing stream (T)

(T)

Wavelength Division Multiplexing: Concept

TRANSMITTERS

RECEIVERS Combining signals

Separating signals

Optical fiber

Wavelength Division Multiplexing: Input Format Independence

SDH IP ATM Leased line ...

TDM vs WDM: Network Evolution 3R

3R

3R

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

N terminals

16 x STM-1

16 x STM-1 16 x STM-1

16 x STM-1 16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

N terminals

16 x STM-1

16 x STM-1 16 x STM-1

16 x STM-1 16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1

16 x STM-1 16 x STM-1

16 x STM-1

STM-16 terminal

TRANSPONDER

TRANSPONDER

TRANSPONDER

WDM

STM-16 terminal 1R

1R

STM-16 terminal 1R

16 x STM-1 16 x STM-1

16 x STM-1

1R

N terminals 16 x STM-1

STM-16 terminal

N terminals

STM-16 terminal

STM-16 terminal

N channels Colored signals with specific wavelengths

16 x STM-1

DWDM: Absorption Spectrum of the Optical Fiber Loss (dB/km)

10 5

S C L 1

0.5

Wavelength (nm) 800

1000

1200

1400

1600

1800

DWDM: C Band

BLUE BAND

1528nm

RED BAND

1546nm

C Band

1564nm

Coarse and Dense Wavelength Division Multiplexing (CWDM & DWDM) Loss

1300

DWDM : ITU G.694.1

1500

1600

50GHz

ie: 80 Channels spaced @ 50Ghz

20 nm

CWDM :

18 Channels spaced @ 20 nm

ITU G.694.2

SDH :

Wavelength

1310nm

1550nm

CWDM versus DWDM systems

Coarse

WDM

Low Cost Equipment • Metro networks • Point-to-point (PTP) topologies • Up to 8 channels with 20nm spacing • Up to 80 km / 20 dB • No Optical Amplification • 10G wavelengths sometimes not ed •

Dense

WDM

More versatile equipment • Metro and long-haul networks • PTP, ring and mesh topologies • Up to 128 channels with 25GHz spacing • Up to 2,000 km • Optical Amplification • up to 100G wavelengths •

Transponder

Client Interface

Standard Receiver Optical Signal

DWDM Interface

2R/3R Regeneration Electrical Signal

B&W Interface

Colored Interface

Electrical Signal

2R/3R Regeneration

Optical Signal

Optimized Receiver

Multiplexer/Demultiplexer  Multiplexing and demultiplexing in a bidirectional communication

Optical fiber

Optical fiber

Optical Amplifier: Applications

TRANSMITTER

Post-amplifier

In-line Amplifier

RECEIVER

Pre-amplifier

Optical Amplifier: Erbium-Doped Fiber Amplifier

ERBIUM-DOPED FIBER AMPLIFIER Signal in

Pump coupler

Signal out Active fiber doped with Erbium ions

Excited state

Pump laser diode

Ground state

electron

Energy supply (pumping)

photon

Spontaneous emission

Noise generation

Signal in

Stimulated emission

Optical amplification

20

Power (dBm/0.25 nm)

Power (dBm/0.25 nm)

Optical Amplifier: Erbium-Doped Fiber Amplifier

WDM multiplex at the input of the amplifier

10 0 -10 -20 -30 -40 1520

1530

1540

1550

1560

1570

Wavelength (nm)

20

Amplifier output

10 0 -10 -20 -30 -40 1520

1530

1540

EDFA

Amplify simultaneously several WDM channels

1550

1560

1570

Wavelength (nm)

Optical Amplifier: Raman Amplification Principle Optical fiber Transmitter

Receiver

1455nm pump

Gain

Gain spectrum versus pump wavelength

@1455nm

@1480nm

(gain)=(pump)+100nm

1450 1470 1490 1510 1530 1550 1570 1590 1610 1630 1650 (nm)

O Concept

O Optical fiber

Amplifier

Amplifier

Optical fiber

 - n

1 , 2 , … , n

1 , 2 , … , n

n

n

DWDM Evolution to RO



First Generation Point to Point WDM: - Installed for capacity exhaust - Strictly point to point applications - Regeneration required for -through wavelengths



Second Generation Fixed Optical (FO): - Optical add/drop via fixed filters - WDM still painful because of: Wavelength stranding in banded add/drop approaches Per wavelength engineering Manual jumper cabling



Third Generation Reconfigurable O (RO): - Dynamic reconfigurable O with single wavelength granularity - Jumper less provisioning - SDH like simplicity for wavelength management

What is a Multi-Degree Node?  A Multi-Degree Node is a Node that allows wavelengths connectivity across several directions  The degree of the Node equals the number of directions  Examples of Multi-Degree Nodes Degree-2

Degree-3

Degree-4

Degree-5

Degree-6

 In a Multi-Degree Node the wavelength connectivity can be managed in a “true” optical domain or after O-E-O conversion

64 | Presentation Title | Month 2009

RO technologies – WSS vs. WB and PLC

•Different RO technologies: • WSS (Wavelength Selective Switch) technology and WSS-based RO

• PLC (Planar Lightwave Circuit) technology and PLC-based RO • WB (Wavelength Blocker) technology and WB-based RO

RO technologies: Wavelength Blocker (WB) Wavelength Blocker: a 1:1 device (1 WDM input, 1 WDM output).



Key WB funtionalities:  Every wavelength coming from the WDM input, can be ed, or blocked.  Every wavelength can be selectively attenuated



Key applications enabled:  Remotely reconfigurable degree-2  Remotely reconfigurable degree-3 nodes are acheivable, however complex and expensive to build.



WDM in

WB does NOT enable:  Colorless or full Tuneable & Reconfigurable O

WB

WDM out

RO technologies: Wavelength Blocker (WB) Example of degree-3 node with WB:  For a degree N node, need Nx(N-1) Wavelength Blockers.   

Degree 3 – 6 WBs needed Degree 4 – 12 WBs needed Degree 6 – 30 WBs needed

 For degrees greater than 2, it becomes very complex and expensive to implement.

W

WB WB

S

E

RO technologies: Planar Lightwave Circuit (PLC)

PLC

Key PLC funtionalities:  Every wavelength coming from the WDM input, can be ed, or blocked. If it is blocked, the corresponding channel can be inserted from the single-λ port  Every wavelength can be selectively attenuated





Single- inputs 1 2 … 40

Key applications enabled:  Remotely reconfigurable degree-2 node  Non-Remotely reconfigurable degree-N nodes

WDM out

Single- in N

WDM in

Single- in 2



Planar Lightwave Circuit: N:1 device (1 WDM input, N-1 single inputs and 1 output).

Single- in 1



WDM OUT

WDM IN

PLC does NOT enable:  Colorless or full Tuneable & Reconfigurable O

= VOA

= 1:2 switch = 100 Ghz MUX(DEMUX)

RO technologies: Planar Lightwave Circuit (PLC) 

Example of degree-4 node

DWDM ring 1

with PLC:

 2 x PLC nodes are present (one per DWDM ring)  Ring interconnections are realized by manual patchcords

 Operator can switch between “” and “drop”. If patchcords are installed, “drop” becomes “switch to other ring”  But “switch to other ring” is only possible for the pre-determined direction!  This is not really a remotely reconfigurable multi-degree node! Fixed patchcords

DMUX#1 drop

PLC#2

add

Degree -1

PLC#1

Degree -2

add

DMUX#3 drop

DMUX#2 drop PLC#4

add

Degree -4

PLC#3

Degree -3

add

DMUX#4 drop

DWDM ring 2

RO technologies: Wavelength Selective Switch (WSS)

Key WSS funtionalities:



Key applications enabled:  Remotely reconfigurable degree-N node (with N>2)  Tuneable & Reconfigurable O

WSS

WDM in 1

WDM in N

 (if used as a N:1 device) it allows to switch individually any wavelength from any input to the output (also more than 1 wavelength can be present at each input)  Every wavelength can be selectively switched, or blocked, or attenuated

WDM in 3



Wavelength Selective Switch: N:1 or 1:N device (N inputs and 1 output, or 1 input and N outputs).

WDM in 2



WDM out

RO technologies: Wavelength Selective Switch (WSS) 2D devices mandatory! array of switching elements (one element per )

input and output fibers

array of collimating lenses

Example of degree-3 node with WSS:

W

WSS WSS WSS S

diffraction grating

 For a degree N node, need N Wavelength Selective Switches 

E

 

Degree 3 – 3 WSSs needed Degree 4 – 4 WSSs needed Degree 6 – 6 WSSs needed

 Creates a simple, high density, easily expandable multi-degree node

WSS-based RO: colorless add/drop



Tunable O (T-O):  2 directions, any channel drop  Fully remotely reprogrammable node:  Tunable filters (Rx)  Tunable laser (Tx)

WSS

DROP

Rx

ADD

Tunable filters

Tx (tunable laser)

Differences between WSS and non-WSS based RO 

WSS  It’s the only technology that allows to implement remotely reconfigurable degree-N nodes (Lower Cost/Less complex)  Allows also to evolve to colorless add/drop implementations



PLC  Usually applied for cost-effective, low-performance degree-2 ROs

 It can be used to implement a non-remotely reconfigurable degree-N node (N>2)  Note: some vendors use an improper terminology, calling “WSS” what is actually a PLC 

WB  Usually applied for degree-2 implementations  It can be used to implement a remotely reconfigurable degree-N node (N>2) however it is costly and complex

WDM Network Typical Link

Management

Traffic Traffic

Traffic

STM16

N channels

OT#2 OT#3

GbE OT#n

OT#i

OT#1

OT#i

Transponder channel i

OT#1 OT#2

D E M U X

Fiber

M U X Booster or Postamplifier

End Terminal

O

ILA

OT#3

PreAmplifier

GbE OT#n

End Terminal

5

WDM Transmission Characteristics You will learn in this chapter … … what the main WDM impairments are … how they can be compensated

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Transmission Quality Parameters: Bit Error Rate



The Bit Error Rate (BER) is a ratio of error bits to total transmitted bits.

Data stream of 1s and 0s

1

0

0

1

1

0

1

Valid range

Transmission Quality Parameters: Eye Pattern

1s are above threshold

Valid range

Decision threshold

0s are below threshold

Transmission Quality Parameters: Q Factor

B

A

A  Q= B

Transmission Quality Parameters: Optical Signal-to-Noise Ratio

Ps

Ps: Signal Power Pn: Noise Power

Pn

OSNR = 10log(Ps/Pn)

WDM Penalties: Optical Noise



The constant amplifier output power (signal + noise) is:  Determined by pumping power.  Self-regulated by amplifier (output power control).



Build-up of noise:  proportional to the number of amplifiers.



As a consequence to the system length increase:  Signal power is decreased.  Amplifier noise is increased.  OSNR is decreased.

Total power

Signal

OSNR

Amplifier noise

Distance

WDM Penalties: Non-Flat Gain  Gain response in a cascade of N repeaters without filters EDFA gain spectrum

Gain (dB)

20

Tx 15

Line

2dB

27nm 1562

10 1525

1535

1545

1555

Wavelength (nm)

1565

Rx

WDM Penalties: Nonlinear Effects



Nonlinear effects tend to manifest themselves when optical power is very high. Therefore, they become important in DWDM systems because of powerful optical devices.



The most important types of nonlinear effects are:     



Self-Phase Modulation (SPM). Cross-Phase Modulation (XPM). Four-Wave Mixing (FWM). Stimulated Brillouin Scattering (SBS). Stimulated Raman Scattering (SRS).

The consequence of nonlinear effects is a pulse widening and so a degradation of the transmission quality.

Transmission Improvement: Forward Error Correction

Transponder Functional Block Diagram Client

B&W Interface

FEC

UFEC

WDM line

Colored Interface

OH

STM-64 Frame

Payload  STM-64

OOB-FEC Frame

FEC

SFEC

Forward Error Correction: Optical Transport Network

OCh Trail OMS Trail TRANSPONDEUR

OTS Trail

TRANSPONDEUR

OMS Trail TRANSPONDEUR

TRANSPONDEUR

TRANSPONDEUR

TRANSPONDEUR

TRANSPONDEUR

TRANSPONDEUR

In-line amplifier TRANSPONDEUR

Line terminal

OTS Trail

TRANSPONDEUR

TRANSPONDEUR

In-line amplifier

Back-to-back terminal

TRANSPONDEUR

Line terminal

Forward Error Correction: ITU-T G.709 Recommendation

    

Optical Transport Hierarchy (OTH), functionality of the overhead, frame structures, bit rates, formats for mapping client signals.

Client

OH

Associated overhead

The ITU-T G.709 recommendation defines the requirements for the Optical Transport Module (OTM) signals in of:

OPUk

OH OH

ODUk OTUk

FEC

OCh

OH Non-associated overhead



OCC OH OH

OCC

OCC

OMSn OTSn

OOS OSC

OTM-n: Optical Transport Module

OPS0

Transmission Improvement: Repeater Design Repeater n-1

Repeater n

Repeater n+1

Optical Amplifier

Bragg Filter

20

3dB

10

+

5 0 -5

20nm

-10

Transmission (dB)

Gain (dB)

15

0.2 0 1545 -0.2

1550

1555

1560

-0.4 -0.6 -0.8 -1

1520 1530 1540 1550 1560 1570 1580

Wavelength (nm)

Wavelength (nm)

1565

Transmission Improvement: Repeater Design [cont.] Repeater n-1

Repeater n

+ A

ex: 0.25dB

A

ex: 0.15dB

F

OA characteristic

Repeater n+1

ex: 0.2dB

+ F

Filter characteristic

Repeater response

Transmission Improvement: Gain Equalization

TEQ

ive

SEQ (ive)

Active

Transmission Improvement: Pre-Emphasis 

Even if there are PEUs, it is necessary to optimize the OSNR per channel.

Input Spectrum

Line

S: Delta Signal

Sp = S/2

Line Sp

S N = S/2

Sp

N

Output Spectrum N: Delta Noise

Sp: Delta Signal Pre-emphasis

Transmission Improvement: Chromatic Dispersion Compensation

TRANSMITTER

RECEIVER

TRANSMITTER

RECEIVER

DCM

DCM

DCM

DCM

TRANSMITTER

RECEIVER

0

Receiver Tolerance X Axis is time and Y Axis is the change in dispersion between modules

Transmission Improvement: Chromatic Dispersion Compensation •

Dispersion Compensating Modules (DCM) added to overcome dispersion limits at pre and post amplification to level off dispersion more uniformly rather than applying all DCM at one side of the span.

•

However DCM adds costs and loss to the system

Dispersion (ps/nm)

1600 1200

800 400 0 0

80

160

240

320

400

Span Length (km) Single Mode Fiber = 17 ps/nm-km

480

System Capacity growth Initial Configuration Bandwith

Btot Channel BitRate : D Spacing : 



Capacity: C = D x Btot/



Capacity Growth: ways and consequences - Increase D



D’ > D B’tot = Btot et ’ = 

 

Fast processing PMD SPM

- Reduce channels spacing  ’ <  B’tot = Btot et D’ = D

Channels filtering  non-linearity (FWM, XPM, Raman) 

- Increase total bandwith Btot  

B’tot > Btot , ’ =  et D’ = D  more channels

large band OA non-linearity (Raman)

WDM System Design WDM

Systems Transmission distance (without OEO regeneration) is limited by  Accumulated Noise Optical Amplifiers  Non Linear Effects

Maximum Transmission Distance depends mainly on:

Distance Max

The

Bit Rate

Nb of channels

System Reach Limitation The Power per channel should be:  High to get the best possible OSNR  Weak to limit the non linear effects

OSNR Limit

System Limit

Emitted Power



OK Non Linearity Limit

Number of amplified spans

6

WDM Network Architecture You will learn in this chapter … … what the architecture of WDM networks is

Proprietary - Use pursuant to Company instructions -All Rights Reserved © Alcatel-Lucent 2011

Global Network Architecture Point-to-point

Long-haul networks Mesh

Inter-metro connections

Residential networks: - DSL - Cable modem

SDH/SONET: - POTS - Wireless

Ring

Inter-metro connections

Inter-metro connections

ISP POP: - IP services

Metropolitan networks

Enterprise : - Frame Relay - ESCON - Fiber Channel - Gigabit Ethernet

Acces networks

Emergence of an Optical Layer

WDM fiber

OXC

Optical Layer Wavelength Division Multiplexing (WDM) Optical protection

O

WDM

O



O





DXC













SDH/SONET Layer Time Division Multiplexing (TDM) High-speed protection Time slot grooming

Service Layer Delivery of services to end s

WDM Applications Metro

Metro

Up to 200km

Traffic Aggregation

Long Haul

Ultra Long Haul

Regional

National & Pan-Continental

Up to 600km

Up to 4500km

Transport

Metro versus Long Haul applications 

Metro / Regional WDM • Typically less than 80 channels • Limited span loss (<30 dB in multispan) • Single or Double stage Amplifier • 40G wavelengths not always ed • Raman not always ed • Alien wavelengths • Choice of DWDM optics types • Non linear effect handled by physical configuration



Long-Haul WDM • Max capacity > 80 channels • Very high span loss (>40 dB in multispan) • Only double stage Amplifier • 40G, 100G wavelengths • Raman amplification • No or restricted use of alien wavelengths • Choice of Modulation formats • Non-linear effect managed by tuning

•The overall link distance is not the sole parameter to choose a solution

Point-to-Point Topology

WDM Terminal

WDM Terminal

WDM Terminal

O

WDM Terminal

Ring Topology WDM HUB

O

O

WDM HUB

Mesh Topology O

O

WDM Terminal

O

WDM HUB

WDM HUB

O

Optical Multiplexing Section Protection (OMSP)

WDM Terminal n°1

Splitter

Tr M U X

WDM Terminal n°2

O.A.

O.A. Working line

Sp

Sw

Tr

O.A.

O.A.

Protecting line

Switch

D E M U X

Tr

Tr

Optical Sub-Network Connection Protection (OSN) SDH

Working line Terminal

Protecting line Terminal

Sp Sw

SDH

Repeater

Repeater

O

O SDH Terminal

Terminal Sp Sw

SDH

Wavelength Protection WDM Terminal n°1

WDM Terminal n°2

Tx

Rx

Rx

Tx

Rx

Rx

Tx

Rx

Rx

Rx

Rx

1:8

1:8 12:1

Tx

N:1

1:N

Tx

Rx

Rx

1+1 Optical Channel Protection

R X From Client

Optical Splitter ½ OP1P1

T X

li

OM

OT

R X

T X

working

li

OM

OT

protection OD

li

R T X X

OT

OD

li

R T X X

1x2 Switch

To Client

½ OP1P1

OT

Lucent Technologies Proprietary

4

Optical Supervisory Channel WDM Terminal n°1

In-Line Amplifier

WDM Terminal n°2

Tr

M U X

O.A.

Tr

OSC System Control Processor

NE Supervision

O.A.

O.A.

OSC System Control Processor

Traffic + OSC

D E M U X

OSC System Control Processor

NE Supervision

Tr

Tr

Telecommunication Management Network

NML Server NOC Station Level

EML Server

Operator PC

Router

Centralized Local (or remote)

HUB

DCN

Craft Terminal

Router

Terminal Station Level

WDM Terminal CT Interface

NOC Interface

Network Element Level

Technical comparison of modulation formats Resilience to OSNR and Nonlinear Effects (I) to OSNR and NonLinear Effects (NLE) are the main factors that limit the maximum transmission reach  1dB less resilience on NLE Effects is as limiting as 1dB less resilience to OSNR

Power per channel [a.u.]

 Resilience

20

Maximum power per channel to limit the nonlinear effects for modulation format “X”

15 10

maximum reach

5 0 -5

Minimum power per channel to guarantee the required OSNR for modulation format “X”

-10 -15 -20 1

3

5

7

9

11

13

15

17

Number of spans

19

21

OSNR AND NLE limit the transmission distance

23

25

Technical comparison of modulation formats Resilience to OSNR and Nonlinear Effects (II) a modulation format guarantees a 3 dB improvement on OSNR resilience but is 3 dB more impacted by nonlinear effects, the maximum reach is the same  Resilience to OSNR is not the only figure to evaluate the maximum reach!

Power per channel [a.u.]

 If

20

3 dB worsening of the resilience to NLE for modulation format “X” vs format “Y”

15 10

maximum reach

5 0 -5 -10

3 dB improvement of the resilience to OSNR (for modulation format “X” vs format “Y”

-15 -20 1

3

5

7

9

11

13

15

17

Number of spans

19

21

OSNR AND NLE limit the transmission distance

23

25