DWDM 101 -...

DWDM 101 BRKOPT-2106

Rodger Nutt

High-End Routing and Optical BU

Technical Leader

© 2013 Cisco and/or its affiliates. All rights reserved. BRKOPT-2106 Cisco Public

Agenda Introduction

– What is DWDM Fiber Types Linear Effects

– The BIG Three: Attenuation, Chromatic Dispersion, OSNR – Solutions to the BIG Three: Optical Amplifiers (EDFA, RAMAN), Dispersion Compensators, FEC

Non-Linear Effects Components

– Transponders / Muxponders / Xponders – Pluggable Optics – Amplifiers – Filters: OADMs / ROADMs, OSC – Protection Schemes

DWDM Software – Automatic Node Setup – Automatic Power Control – Automatic Laser Shutdown – WSON/GMPLS

3

What is DWDM?


Wavelength Division Multiplexing

5

DWDM systems use optical devices to combine the output of several optical transmitters

Optical fiber pair

TX

Optical transmitters

Optical receivers

TX

TX

TX

RX

RX

RX

RX Transmission

DWDM devices


ITU-T Grid

6

Frequency (THz)

Wavelength (nm)

1528.77 nm 1578.23 nm

0.4 nm spacing

1552.52 nm (Center channel)

196.2 THz 190.1 THz 193.1 THz (Center channel)

50 GHz spacing

ITU wavelengths = lambdas = channels center around 1550 nm (193 THz)


Dense vs. Coarse (CWDM vs. DWDM)

7

DWDM CWDM Application Long Haul Metro Amplifiers Typically EDFAs Almost Never # Channels Up to 80 Up to 8 Channel Spacing 0.4 nm 20nm Distance Up to 3000km Up to 80km Spectrum 1530nm to 1560nm 1270nm to 1610nm Filter Technology Intelligent Passive

Optical Fiber


Fiber Geometry and Dimensions

9

The core carries the light signals

The refractive index difference between core & cladding confines the light to the core

The coating protects the glass

Coating 250 microns

Cladding 125 microns

Core SMF 8 microns


Communication Wavelengths in the InfraRed

850 nm Multimode 1310 nm Singlemode C-band:1550 nm Singlemode L-band: 1625 nm Singlemode

UltraViolet InfraRed

850 nm 1310 nm 1550 nm 1625 nm

λ

Wavelength: λ (nanometers)

Frequency: ƒ (terahertz)

C =ƒ x λ

Visible

Optical Spectrum

10

© 2013 Cisco and/or its affiliates. All rights reserved. BRKOPT-2106 Cisco Public The primary difference is in the Chromatic Dispersion Characteristics

Good for TDM at 1310 nm OK for TDM at 1550 nm OK for DWDM (With Dispersion Mgmt. Good for CWDM (>8 wavelengths)

Extended Band (G.652.C) (suppressed attenuation in the traditional water peak region)

OK for TDM at 1310 nm Good for TDM at 1550 nm Good for DWDM (C + L Bands)

NZDSF (G.655)

OK for TDM at 1310 nm Good for TDM at 1550 nm Bad for DWDM (C-Band)

DSF (G.653)

Good for TDM at 1310 nm OK for TDM at 1550 OK for DWDM (With Dispersion Mgmt.)

SMF (G.652)

Applications for the Different Fiber Types

11

Linear Effects


Transmission Impairments

Attenuation – Loss of Signal Strength

Chromatic Dispersion (CD) – Distortion of pulses

Optical Signal to Noise Ratio (OSNR) – Effect of Noise in Transmission

800 900 1000 1100 1200 1300 1400 1500 1600Wavelength (nm)

0.2

0.5

2.0

Loss (dB/km)

L-ba

nd:15

65–1

625n

mC-

band

:1530

–156

5nm

S-ba

nd:14

60–1

530n

m

800 900 1000 1100 1200 1300 1400 1500 1600Wavelength (nm)

0.2

0.5

2.0

Loss (dB/km)

L-ba

nd:15

65–1

625n

mC-

band

:1530

–156

5nm

S-ba

nd:14

60–1

530n

m

Time Slot

10Gb/s

2.5Gb/s Fiber

Fiber

Time Slot

10Gb/s

2.5Gb/s Fiber

Fiber

S+N

N

S+N

N

13


Attenuation

14

With enough attenuation, a light pulse may not be detected by an optical receiver

Insertion loss (dB)

Attenuation (dB)

Distance (km)

Optical device


Fiber Attenuation (Loss) Characteristic

15

800 900 1000 1100 1200 1300 1400 1500 1600

OH- Absorption Peaks in Actual Fiber Attenuation Curve

Wavelength in Nanometers (nm)

0.2 dB/Km

0.5 dB/Km

2.0 dB/Km

Loss(dB)/km vs. Wavelength S-band:1460–1530nm

L-band:1565–1625nm

C-band:1530–1565nm OH: Hydroxyl ion absorption is the absorption in optical fibers of electromagnetic waves, due to the presence of trapped hydroxyl ions remaining from water as a contaminant.


Laser Output Power and Receiver Sensitivity and dBm

Fiber loss expressed in dB but transmitter/receiver power is expressed in dBm This is why both the transmitter output power and the receiver sensitivity is

expressed in dBm:

PowerdBm=10log(PmW/1mW)

dB and dBm are additive, hence the simplification

Example: • Powerdbm = 10log(2mW/1mW)=3dBm • Powerdbm = 10log(1mW/1mW)=0dBm

16


Gain can be expressed by the ratio of Pout/Pin

Gain is measured more conveniently in dB , calculated by 10 log10 Pout/Pin

If the power is doubled by an amplifier, this is +3 dB

Amp Pin Pout

Gain and Decibels (dB)

17


Attenuation: Optical Budget

18

Optical Budget is affected by: – Fiber attenuation – Splices – Patch Panels/Connectors – Optical components (filters, amplifiers, etc.) – Bends in fiber – Contamination (dirt/oil on connectors)

Basic Optical Budget = Output Power – Input Sensitivity

Pout = +6 dBm R = -30 dBm

Budget = 36 dB


Signal Input

980 or 1480 nm Pump Laser

Erbium Doped Fiber

Amplified Signal Output

Isolator

WDM Coupler for pump and signal

Isolator

Erbium doped fiber amplifies optical signals through stimulated emission using 980nm and 1480nm pump lasers

Basic EDFA configuration

Attenuation Solution: EDFA

19


Chromatic Dispersion (CD)

Total dispersion is a function of the length of fiber and it’s dispersion factor Limits transmission distance for 10G and above wavelengths Can be compensated by using negative dispersion fiber or electronically

through modulation schemes

20

Bit 1 Bit 2 Bit 1 Bit 2 Bit 1 Bit 2 Bit 1 Bit 2 Bit 1 Bit 2

The Optical Pulse tends to Spread as it propagates down the fiber generating Inter-Symbol-Interference (ISI)


DCUs use fiber with chromatic dispersion of opposite sign/slope and of suitable length to bring the average dispersion of the link close to zero.

Solution: Dispersion Compensating Unit

21


Optical Signal-to-Noise Ratio (OSNR)

22

OSNR is a measure of the ratio of signal level to the level of system noise

As OSNR decreases, possible errors increase

OSNR is measured in decibels (dB) EDFAs are the source of noise

Signal level dBm)

Noise level (dBm)

Signal level OSNR = ----------------- Noise level


Optical Signal Detection

23

Across a fiber span, optical signals encounter attenuation, dispersion, and increased noise levels at amplifiers.

Each of these factors causes bit detection errors at the receiver.

Distance (km) Transmitting end

Receiving end

Low attenuation Low dispersion High OSNR

High attenuation High dispersion Low OSNR


Example: Link Design with Line Amplifiers

24

10G Xenpak spec: Tx: +3 to -1dBm, Rx min: -21dBm (0ps/nm) CD tolerance: +1600ps/nm @ 2dB penalty OSNR min: 16dB (0.5nm resolution)

-1dBm +2dBm 0ps/nm

Time Domain

Wavelength Domain

OSNR: 18dB Rx: -9dBm

Meets receiver minimum OSNR and power requirement

+2dBm/ch

TX RX Tx: -1dBm min

Mux

Dem

ux

DCU -1600 ps/nm 25dB 25dB

DCU -1600 ps/nm

+2dBm/ch -23dBm/ch -23dBm/ch

OSNR= 21dB

Noise

OSNR= 18dB

Noise

OSNR= 35dB

Noise

-23dBm 1600ps/nm

+2dBm 0ps/nm

-23dBm 1600ps/nm

+2dBm 0ps/nm


OSNR Solution #1 Raman Amplifier

25

Stimulated Raman Scattering creates the Gain

Reduces the effective span loss and increases noise performance

Gain is highly dependent on quality of fiber

Gain Spectrum ~ 40nm with a single pump


Log

(BER

)

4 5 6 7 8 9 10 11 12 13 14 15 –15 –14 –13 –12 –11 –10

–9 –8 –7 –6 –5 –4 –3 –2 –1 0

S/N (dB)

Uncoded No FEC

G.709 RS(255,239)

Raw Channel BER=1.5e-3

EFEC=8.4 dB FEC=6.2 dB

OSNR Solution #2: Forward Error Correction

26

FEC extends reach and design flexibility, at “silicon cost”

G.709 (G.709 Annex A) standard improves OSNR tolerance by 6.2 dB (at 10–15 BER)

Offers intrinsic performance monitoring (error statistics)

Higher gains (8.4dB) possible by enhanced FEC (with same G.709 overhead – G.975.1 I.4)

Benefit: FEC/EFEC Extends Reach and Offers 10–15 BER

Non-linear Effects


Non Linear Effects

Polarization Mode Dispersion (PMD) – Caused by Non Linearity Of

Fiber Geometry – Effective for Higher Bit rates (10G)

Four Wave Mixing (FWM) – Effects in multi-channel systems – Effects for higher bit rates

Self/Cross Phase Modulation (SPM, XPM) – Effected by high channel power – Effected by neighbor channels

28

Wavelength (nm)

-5

-10

-15

-20

-25

-30

-35

-40

1542 1543 1544 1545 1546 1547 1548

Powe

r (dB

m)

Wavelength (nm)

-5

-10

-15

-20

-25

-30

-35

-40

1542 1543 1544 1545 1546 1547 1548

Wavelength (nm)

-5

-10

-15

-20

-25

-30

-35

-40

1542 1543 1544 1545 1546 1547 1548

Powe

r (dB

m)

nx

nyEx

Ey

Pulse As it Enters the FiberSpreaded Pulse As it Leaves the Fiber

nx

nyEx

Ey

Pulse As it Enters the FiberSpreaded Pulse As it Leaves the Fiber

Power SPM

Disto

rtion

Power SPM

Disto

rtion


Polarization Mode Dispersion (PMD)

It is Relevant at Bit Rates of 10Gb/s or More Pulse broadens as it travels down fiber Mainly a manufacturing/install issue with concentricity of fiber

29

nx

ny Ex

Ey

Pulse as It Enters the Fiber Spreaded Pulse as It Leaves the Fiber


Laser

10Gb/s

QPSK1 Modulator 10Gb/s

40Gb/s = 10Gbaud 10Gb/s

QPSK2 Modulator 10Gb/s

PMD Solutions

Increase system robustness with FEC Leverage MLSE Use PMD Compensation (PMDC) Deploy PMD-optimized fibers Advanced Modulation Schemes

30

DWDM Components


Typical Components of DWDM Systems

Optical transmitters and receivers DWDM mux/demux filters Optical add/drop multiplexers (OADMs) Reconfigurable OADM (ROADM) Optical amplifiers Transponders/Muxponders

32


Optical Transmitter Block Diagram

33

Detects pulses of electrical charge

• Power measured in watts (W) • Amplitude measured in

volts (V)

Creates pulses of light • Power measured in

decibel-milliwatts (dBm) • Relative amplitude

measured in decibels (dB)

Electrical conductor

E-O

Optical fiber

1 1 1 0 1 1 1 0 Electrical-to-optical (E-O) conversion

+

- dB

+

- V + -


Optical Receiver Block Diagram

34

Detects pulses of light • Power measured in

decibel-milliwatt (dBm) • Relative amplitude

measured in decibels (dB)

Creates pulses of electrical charge • Power measured in watts (W) • Amplitude measured in volts (V)

Electrical conductor

O-E

Optical fiber

+ -

Optical-to-electrical (O-E) conversion 1 1 1 0 +

- dB

1 1 1 0 +

- V


Problem: DSP electronics (required for above) not yet capable of processing 100Gb/s serial data rates

Solution: Dual Polarization DQPSK Modulation, allows single wavelength 100G transmission with a baud rate of ~28Gb/s

This is a Modulation (TX) function

100 Gigabit DWDM Transmission

35

Problem: Transmission impairments increase significantly at higher bit rates (CD, PMD, non-linear effects)

Solution: Compensate for these impairments with intelligent Digital Signal Processing, enabled by Coherent Detection

This is a Demodulation (RX) function


100G Technology – Coherent Detection

36

Direct Detection • Must correct for impairments in the physical domain (insert DCU’s) • Forced to live with non-correctable impairments via network design (limit

distance, regenerate, adjust channel spacing) • Dumb detection (OOK), no Digital Signal Processing, only FEC

Coherent Detection • Moves impairment correction from the optical domain into the digital domain • Allows for digital correction of impairments (powerful DSP) vs. physical correction of

impairments (DCU’s). Adds advanced FEC. • Massive performance improvements over Direct Detection.

DD

CD

DD

DCU DCU DCU

Regen


DWDM Mux and Demux Filters Block Diagram

37

1

2

3

N

DWDM fiber

N light pulses of different wavelengths

From N transmitters

To N receivers

1

2

3

N

Composite signal

Multiplexer Demultiplexer

1, 2, ….N


OADM Block Diagram

38

New data stream, same wavelength

Signsl 1 drop

OADM one signal

Pass through path Original composite signal

New composite signal

Drop path Add path

DWDM fiber

Signal 2 add


ROADM Architecture

39

Add Wavelengths

Drop Wavelengths

Pass-Through Wavelengths Splitter

Add Wavelengths Software

Controlled 32 Ch. DeMux

Pass-Through Wavelengths Splitter

λ1 Network Element λ3

Network Element

Software Controlled Selectors – 32 Ch. (Pass-through/Add/Block)

DWDM Signal

Transponder Module

West

East DWDM Signal

Drop Wavelengths

drop block block drop

drop block block drop

Software Controlled

32 Ch. DeMux

Add

Pass

Add

Pass

Network Element

Network Element

Transponder Module

Pass

Pass

Add

Add

Software Controlled Selectors – 32 Ch. (Pass-through/Add/Block)

λ1 λ3


Optical Amplifer Block Diagram

40

Unidirectional operation

Extends the reach of a DWDM span

OA

DWDM fiber

Attenuated input composite signal

Amplified output composite signal

Powerin Powerout


Transponder Block Diagram

41

Optical fiber

Non-ITU-T compliant wavelength

ITU-T compliant wavelength

O-E-O wavelength conversion

850, 1310, 1550 nm 15xx.xx nm Transponder

Tx

Rx G.709 Enabled


Muxponder Block Diagram

42

Optical fibers

Multiple Non-ITU-T Compliant Clients

ITU-T compliant wavelength

Multiplexing and O-E-O wavelength conversion

850, 1310, 1550 nm 15xx.xx nm Tx

Rx

Muxponder

G.709 Enabled


Pluggable Optics

10G XENPAK, X2, XFP and SFP+

Below 10G GBIC and SFP

40G/100G CFP and CXP

43


DWDM System

44

OEO Tx Rx

Tx Rx

OADM OA OA

Rx Tx

Transponder interface

OEO Tx Rx

Tx Rx

Direct interface To client devices

Client Client

Mux and demux

Mux and demux


Optical Protection Scheme Options

45

• Platinum-Available network: Combination

of multiple protection scheme • Gold-Available network: Y-cable protection • Silver-Available network: Optical Trunk

Protection • Bronze-Available network: Multiple Section

Protection • Available network: Transport Section

Protection

Gold-Available

Bronze-Available

Silver-Available

Platinum-Available

DWDM Software


Intelligent DWDM

Modern systems compensate real-time for variations in the network – Gain Equalization – Amplifier Control – Automatic Node Setup – Automatic Power Control Allows for less truck rolls and maintenance windows

47


Why Per-Channel Optical Power Equalization • For amplifiers to operate correctly, all channels must be equalized in power.

• If channel powers are not equal, more gain will go to the higher powered channels.

• Channel power is inherently unequal due to different insertion losses, different paths (add path vs. express/pass-through), etc.

• Controlling the optical power of each channel in an optical network is required.

AMP

AMP

Optical Power Equalized Channels

Channels with Unequal Optical Power

OADM Without Power Equalization

Express Path

Add/Drop Path

Why Per Channel Equalization

48


OADM Without Power Equalization

Express Path

Add/Drop Path

Example

49

AMP AMP

OADM With Power Equalization

Express Path

Add/Drop Path

AMP AMP


ANS Example

50

Express Path

Add/Drop Path

AMP AMP

T3

T Target Power

T2

T1

VOA

T4

ANS Target Powers

Per Channel Power

T1 +2dBm

T2 -16dBm

T3 -9dBm

T4 +2dBm

Express Path VOA Constant Attenuation

L1

L2

L3

Loss dB

L1 (Express Drop) 2.5dB

L2 (Per Ch Add) 5.0dB

L3 (Express Add) 2.5dB

L4 (Per Ch Drop) 5.5dB

VOA dB

Express Path VOA 6dB

Add VOA N/A (depends upon laser TX power

Drop VOA 12.5dB (Start point)

Add/Drop VOA Constant Power

L4

• Target Power comes from design tool or Measured Span Loss Values from System • Loss values are measured and stored in the OADM(s) / ROADM(s) • Constant Attenuation VOA’s set via ANS software logic • Constant Power VOA’s set to close loop Loss L


Constant Power Mode

51

AMP

Initial condition – 2 channels

Total Output Power +2dBm

Per Channel Power -1dBm

AMP

Adding 2 channels Amp set to Constant Power Mode



Add Channels Example

AMP

Initial condition – Gain 14dB




AMP





Span Loss Increase Example




Constant Gain Mode

52

AMP




AMP

Gain Stays Constant – Gain 14dB



Add Channels Example

AMP





AMP

Gain stays the Same – Gain 14dB

Total Output Power -1dBm




Span Loss Increase Example



Automatic Power Control

53

Automatically corrects amplifier power/gain for capacity change, ageing effects, operating conditions

Keep traffic working after network failires

Prevent BER due to network degrade

Keep constant either power or gain on each amplifier

No truck rolls No troubleshooting required No operation complexity

APC

No Human Intervention Required


Automatic Laser Shutdown (ALS) w/ Booster

54

ALS is required to decrease the risk of laser damage to the human eye

The complete sequence of events is completed within 1s as required by IEC 825-2

This is not possible on passive dwdm systems

OSCM

OPT-BST Node B East side

OPT-PRE P

P

OSCM

OPT-BST

Node A West side

OPT-PRE

Fiber cut

Amplifier Automatic Lasers Shutdown

Payload (LOS-P) & OSC (LOS-O) detected

1 1

Loss Of Signal (LOS) is declared

1


P P


Payload (LOS-P) & OSC (LOS-O) detected 1

1

Loss Of Signal (LOS) is declared 1


LOS-O is detected

OSCM Automatic Laser Shutdown

LOS-O is detected

OSCM Automatic Laser Shutdown


Dynamic Optical Restoration Touchless Optical Layer + Embedded WSON Intelligence

ONS 15454 MSTP

Client

Colorless, Omni-Directional ROADM switches the path Service is brought back up with the same Client and Optical interfaces, zero touches

Embedded WSON intelligence locates and verifies a new path Edge Nodes instruct client to re-tune its wavelength

Fiber Cut!

animated slide

Client

IPoDWDM IPoDWDM

55


Session Summary

Dramatic increase in Bandwidth has led to the use of DWDM Fiber type effects the quality of transmission Linear Effects are predictable and can be compensated Non-Linear Effects are known but somewhat unpredictable Modern DWDM systems are intelligent and simple to operate Good reference is:

http://www.cisco.com/en/US/products/hw/optical/ps2011/products_technical_reference_chapter09186a00802342dd.html

56


Glossary Arrayed Waveguide (AWG) Automatic Node Setup (ANS) Automatic Power Control (APC) Chromatic Dispersion (CD) Cross Phase Modulation (XPM) Decibels (dB) Decibels-milliwatt (dBm) Dense Wavelength Division Multiplexing (DWDM) Dispersion Compensation Unit (DCU) Dispersion Shifted Fiber (DSF) Erbium Doped Fiber Amplifier (EDFA) Four-Wave Mixing (FWM)

57


Glossary

International Telecommunications Union (ITU)

Non-Zero Dispersion Shifted Fiber (NZ-DSF)

Optical Add Drop Multiplexer (OADM)

Optical Signal to Noise Ratio (OSNR)

Optical Supervisory Channel (OSC)

Optical Supervisory Channel Module (OSCM)

Polarization Mode Dispersion (PMD)

Reconfigurable Optical Add Drop Multiplexer (ROADM)

Self Phase Modulation (SPM)

Single Mode Fiber (SMF)

Variable Optical Attenuator (VOA) 58


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