optical monitoring

8/12/2019 Optical Monitoring

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CIAN Supercourse 2011

Optical Performance Monitoring toEnable Robust and Reconfigurable

Optical Networks

Alan Willner

University of Southern California

Los Angeles, CA 90089-2565


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USCs OCLab


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Outline

1. Overarching Perspective

2. Optical Performance Monitoring- optically-assisted techniques

- receiver based techniques


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Differential Phase-Shift-Keying (DPSK)

DPSK

t

1 1 0 1 00

RZ-DPSK

t

1 1 0 1 00

Pulse appears in every bit

Constant optical power

Energy is information.

Information is sent during 0 bits.


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Multi-level Modulation Formats in Optics

Benefits from coherent detection:

More effective for pol-demuxing Digital processing for mitigation

1 bit/symbol 2 bits/symbol 4 bits/symbol~112 Gbaud

OOK

DPSKDB/PSBT

~56 Gbaud

DQPSK

(4-ASK)

~28 Gbaud

PDM-(D)QPSK

(16-DPSK)

"#$%&'

()$%&'

( )

"#$%&'

()$%&'

"#$%&'

()$%&'

"#$%*'

()$%*'

8 bits/symbol~14 Gbaud

16-QAM

8-PSK/2-ASK

"#$%&'

()$%&'

"#$%*'

()$%*'

!"#"$"%&"' )* +,%-"$. /0&12"0345&"%2. 678 9


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DPSK & DQPSK

T

-

DPSK

Re{E}

Im{E}

! 3-dB sensitivity improvement! Less sensitive to nonlinearity

! ! 0 0

Input signal

1 1

1 1

0 1 0

T

-

DQPSK

Re{E}

Im{E}

! Spectrally efficient - 2 bit/s/Hz! Tolerant to dispersion

Input

signal

T

-

+45

-45

I

I

Q

Q

I

Q

T


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Polmux Concept

0001

11 10

000001

011 010

100

101

111 110

Regular (D)QPSK

2 bits per symbol

Polmux (D)QPSK

3 bits per symbol

polarization

axis

polarization

axis

Polarization is another dimension to carry information, so Polmux is more spectrally efficient.


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DPSK & Polarization-Multiplexing

T

-

D(Q)PSK

Re{E}

Im{E}

! Less sensitive to nonlinearity! 3-dB sensitivity improvement

! ! 0 0

Input signal

1 1

1 1

0 1 0

T

Pol-muxing doubles the spectral efficiency!

enhanced performance

Pol-muxed

DPSK channelPC

PC PBC

DPSK

DPSK

H

V

t

t

H

V

t

PBS

DPSK

DPSK

PC

H

t

V

t

Transmitter Receiver

Data 1

Data 2


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Latest Results on High Capacity/S.E. Transmission

32Tb/s PDM-RZ-8QAM over 580km Ultra-low-loss Fiber

PDM-RZ-8QAM Digital coherent detection EDFA-only Amplification 25GHz-spaced 320x114Gb/s length / loss ratio82.8km / 14.6dB

X. Zhou, OFC 2009 PDP

72x100Gb/s over 7040km Large Effective Area Fiber

G. Charlet, OFC 2009 PDP

100Gb/s channels

88x80km distance Raman-Erbiumamplification

coherent receiver


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10 bit/s/Hz Spectral Efficiency

Spectral Efficiency

" Challenge: to explore multilevel optical modulation formats" Pack more bits per symbol: DQPSK, APSK, OFDM, QAM" Powerful tool: orthogonal modulation

Improving Spectral Efficiency

Pol-Mux 1 Gsymbol/s, 128 QAM

(14Gbit/s) (BW: 1.4 GHz)

Several Examples

ModulationSpectral

EfficiencyReference

10!112 Gbit/sPolMux16-QAM

6.2 bit/s/HzA. H. Gnauck

PDPB82009

8!

65.1 Gbit/scoherentPolMux-OFDM

7 bit/s/Hz H. TakahashiPDPB7OFC2009

PolMux1Gsymbol/s128 QAM14 Gbit/s

10 bit/s/HzH. GotoJThA45

OFC2008

To date, largest spectral efficiency


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Predictedbursting of bubble in 97


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Heterogeneous Systems: One Network Fits All

Future

Heterogeneous

Network

Economics: Early market entry of new services (CATV??)

Variable QoSDifferent

Modulation Formats

Multiple

Wavelength Ranges

Circuit +PacketSwitching?

Variable

Bit Rate

Sub-carrier

Multiplexing

(D+A)?

Hardware should be reconfigurable and transparent An intelligent network could use the optimalmethod fromthe application/user viewpoint.


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Think wireless laptop LAN


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Self-Managed Networks

Adaptive Resources Diagnose and repair BW allocation Gain/Loss

Dispersion Compensation -Routing

Look-up tables

A

C

D

B

E

Today :Measure, Make,

Tweak, Pray.

Automation + Intelligence + Monitoring

Keep the person out of the loop


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Monitoring the State of the Network

UbiquitousMonitoring

Monitor non-catastrophic datadegradation

Isolate specific impairments

Detect

Attacks

Locate

Faults

Diagnose &

Assess Repair

DamageReroute &

Balance Traffic

Window of operability is shrinking Monitoring is required

Ubiquitous deploymentGraceful routing based onphysical state of network?

Telcos: Human Error(~1/3 of outages)

MaliciousBehavior


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OPM

CD PMD OSNR Power Crosstalk

Hardware# Optical/RF filter# Low-speed detectorSoftware# Pattern recognition

using neuron networks

and data constellations

Spec# Update rate# Isolation# Advanced modulation

format

# One or more faults

NC & MActions Impacted by OPM

What impairment is affecting the traffic/data? Should compensation be tuned? Should format/rate be changed? Should QoS be changed? Should routing table be changed?

Network &

Switching Fabric

Determine each parameter:

For example:

Level 0 = no problem Level 10 = channel outage

Design of Optical Performance Monitor

PARAGON


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Monitoring for an Efficient Network

Robert Shapiro, former Undersecretary of Commerce:

Accommodating the fast-rising demands on bandwidth willrequire a significant acceleration in industry investments totaling $300 billion to $1 trillion for the US.

$Operate closer to the red line.$Less need to over-build.$Increase mean-time-to-failure.$Decrease mean-time-to-repair.$Decrease human error.


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Multivariable Routing

< j, #j>

a. Fiber length

b. Signal degradationc. Amplificationand transients

" Component non-idealities# Signal degradation

# Each link and node has a set of parameters (a, b, c)# Must interpret the cost function for routing table# Determine ranges of these parameters for

inclusion into network model

Interoperability with fiber plant # of nodes

Size of network


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Outline





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Optical Signal-to-Noise Ratio


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Arbitrarily

Polarized signal+

Unpolarized noise

Polarization

controller

Ps + Pase

Polarizer

(Parallel)

Polarizer

(Orthogonal)

Ps + 0.5*Pase

0.5*Pase

Y. C. Chung et. al., JLT, 2006

! The received signal (together with noise) is split into two orthogonalpolarization components.

! The polarization ratio is a measure of the OSNR (Ps/Pase).! The performance could be affected by various polarization effects.

OSNR Monitoring Using Polarization Nulling

Transparent to multiple input data format and bit rate


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! Using partial bit delay-line Interferometer (DLI)! OSNR is proportional to the Ratio (=Pconst/ Pdest)!Applicable to OOK, DPSK data

Y. Lize, et. al., PTL 07 and JLT 08

OSNR Monitoring for Multiple Modulation Formats

T

PowerMeter

Power

Meter

Pconst

Pdest

Input

signaldelay

)2

1

4

1(

)2

1

4

3(

PP

PP

noisesignal

noisesignal

Ratio

+

+

=

Signal has coherent interference, noise doesnt


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! Using partial bit delay-line Interferometer (DLI)! OSNR is proportional to the Ratio (=Pconst/ Pdest)!Applicable to OOK, DPSK data

Y. Lize, et. al., PTL 07 and JLT 08

OSNR Monitoring for Multiple Modulation Formats

FSR=1/T

Constructive portDestructive port Monitor tones to isolate-- CD and PMD

Insensitive to CD and PMD DB / AMI have tones OSNR -- only S coherent, not N

T

PowerMeter

Power

Meter

Pconst

Pdest

Input

signaldelay


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Channel Monitoring using Integrated Filters

)2

1

4

1(

)2

1

4

3(

PP

PP

noisesignal

noisesignal

Ratio

+

+

=

OSNR:Signal has coherent interference, not noise

CD & PMD

Tones affected differently by CD & PMDY. Lize, et. al., PTL 07 and JLT 08


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Dependence on Chromatic Dispersion

Temperature Dependence

-100

-50

0

50

100

-40 -30 -20 -10 0 10 20 30 40

DispersionChang

e,

D(ps/nm)

NRZ 40 Gbit/s Limit

L=1000 km

L=500 km

L=200 km

Dispersion Slope ~ 0.08 ps/nm2km

d0/dT ~ 0.03 nm/CNRZ 40 Gbit/s Limit

-100

-50

0

50

100

-100

-50

0

50

100

-40 -30 -20 -10 0 10 20 30 40-40 -30 -20 -10 0 10 20 30 40

DispersionChang

e,

D(ps/nm)

NRZ 40 Gbit/s Limit

L=1000 km

L=500 km

L=200 km



Temp Change, C

Temperature Dependence

-100

-50

0

50

100

-40 -30 -20 -10 0 10 20 30 40

DispersionChang

e,

D(ps/nm)

NRZ 40 Gbit/s Limit

L=1000 km

L=500 km

L=200 km



-100

-50

0

50

100

-100

-50

0

50

100

-40 -30 -20 -10 0 10 20 30 40-40 -30 -20 -10 0 10 20 30 40

DispersionChang

e,

D(ps/nm)

NRZ 40 Gbit/s Limit

L=1000 km

L=500 km

L=200 km



Temp Change, C

Data Rate Dependence

Dispersionps

nmkmBit-Rate

Doubled

Time Half Freq. Double

-1/T 1/T0-1/2T 1/2T-1/T 1/T0-1/2T 1/2T

Penalty increases

FOURtimes

Time Freq

Data Rate Dependence

Dispersionps

nmkmBit-Rate

Doubled

Time Half Freq. Double

-1/T 1/T0-1/2T 1/2T-1/T 1/T0-1/2T 1/2T

Penalty increases

FOURtimes

Time Freq


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Vestigial Sideband Optical Filtering

Frequency

BW

$f

VSB-UVSB-L

Optical Carrier

fU f0 fL


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Time delay ( t ) between two VSB signals is a function of

chromatic dispersion

Bits can be recovered from either part of the spectrum

40-Gb/s

RZ Data

VSB-L

VSB-U

f

Dispersion

f

O/E t

Chromatic DispersionMonitoring Using Clock Phase

Isolate CD from PMD effects Low cost

Q. Yu, JLT, Dec., 2002

Filteredspectrum

Entirechannel

Filteredspectrum

0 50 100 1500.0

0.5

1.0

1.5

Intensity

Time (ps)

0 50 100 1500.0

0.5

1.0

1.5

Intensity

Time (ps)

Q. Yu, JLT, 2003


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Polarization Mode Dispersion (PMD)cross section

Elliptical Fiber Core

side view

PMD induces randomlychanging degradations.

Critical limitation at>10 Gbit/s data rates.

The 2 polarization modes propagate at different speeds.

1st-order PMD = DGD

Probability of Exceeding a Specific DGD (%)

0 10 20 30 40 50

0.111050

Maxwelliandistribution

tailProb

ability

Distribution

0 10 20 30 40 500 10 20 30 40 50

0.111050

Differential Group Delay (ps)

Maxwelliandistribution

tail

Significant higher-order effects can exist.


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In Phase

t

tAxis 2

Axis 1

Out of Phase

$%

Axis 2

Axis 1

CarrierUpperclock

Lowerclock

PMD

(AxisDelay)

Power

f

CD

(Freq.

Delay)

In Phase

t

tLower

Upper

Out of Phase

$%

Lower

Upper

Two Clocks

Upper Clock

RF Clock Tone Fading


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PMD Monitoring by Narrowband Filtering

Opticalspectrum

detection

ElectricalDomain

Clock fadeswith

PMD & CD

detection

Clock fadeswith

PMD only

w/o filter

w/ partial filtering

SMF

Upper & Lower Clocks

Only Upper Clock

T. Luo, et al., PTL, 2004

-30

-20

-10

0

0 10 20 30 40 50

w/ filter

DGD (ps)

RelativeClock

Power(dB)

DGD (ps)

RelativeClockPower(dB)

320 ps/nm

0 ps/nm

640 ps/nm

-30

-20

-10

0

0 10 20 30 40 50

w/o filter

CD = 0 ps/nm

320 ps/nm

640 ps/nm

~20d

B

< 3 dB

f


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T

Power

Meter

Power

Meter

Const.

Dest.Input

signal

OSNR monitor Processing

Partial bit

Power ratio of twoports indicates OSNR.

This OSNR monitor istransparent to various

data formats.

OPMs Using Delay-Line Interferometer


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Channel Monitoring using Integrated Filters

)2

1

4

1(

)2

1

4

3(

PP

PP

noisesignal

noisesignal

Ratio

+

+

=

OSNR:Signal has coherent interference, not noise

CD & PMD

Tones affected differently by CD & PMDY. Lize, et. al., PTL 07 and JLT 08


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11/7/11 34

PMD Monitoring of Phase-Modulated

Data Using Interfermetric Filter

! The two outputs of the PBS represent the constructive and destructive filtersof a standard Mach-Zehnder delay-line interfometer (FSR = 1/!").

! At the destructive port, the monitored RF power will change with the DGD-generated interferometric filter response.


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11/7/11 35

Experimental Results

The RF power measured at 170 MHz increases by ~ 20 dB in thepresence of 0 to 100 ps of DGD.

Chromatic dispersion-insensitive measurements to be within + 1 dB.

DGD (ps)

0 20 40 60 80 100

RFPow

er(dBm)

-40

-45

-50

-55

-60

-65

-70

RFPow

er(dBm)

-40

-45

-50

-55

-60

-65

-70

Chromatic Dispersion (ps/nm)

0 100 200 300 400 500 600 700

10-Gb/s NRZ-DPSK

20-Gb/s NRZ-DQPSK

J.-Y. Yang et. al., PTL, 2008


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Significance of Higher-order PMD

Ref: M. Karlsson, et al., Optics Letters, 1999;

H. Kogelnik, et al., JLT 2003.

"It is sometimes stated that once the signal bandwidth is large enough for second-order PMD

to be important, then all other higher order terms become important too. If this were strictly

true, then higher order PMD compensation would be a hopeless task there is a need for

closer examination of these bandwidth limitations.

$&

ACF

(ps2) $&PSP

-H. Kogelnik, et al., JLT 2003

PSP Bandwidth

Autocorrelation Function of PMD Vector Higher-orders become

important if signal BW

> $&PSP

Theory

Measurement

Fiber typeOld fiber

PMD = 0.5 ps/km1/2

New fiberPMD = 0.1 ps/km1/2

Future fiberPMD = 0.05 ps/km1/2

1 Tb/s Transmission

Limit due to PMD40 m

1 km

4 km


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Combined Effects of PMD and PDL

Polarization Mode Dispersion

Polarization Dependent Loss (PDL)

Optical

Components

(PDL=? dB)

$%Different

Attenuation

PSP1 (PSP2

Differential

Group Delay

PSP1(PSP2

Fiber with high PMD

PSP1

PSP2

PSP 1

PSP2

PSP1

PSP2

PSP1(PSP2

PDL:

Frequency-dependent

attenuation

PMD:

Enhanced time spreading

B. Huttner, et al., JSTQE, 2000

L.-S. Yan, etal., PTL, 2003


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Combined Effects of PMD and PDL

Probability density function of 15 PMD sections

Without PDLWith 15 PDL sections

(each: 0.2 dB)

L.-S. Yan et. al., JLT 2004


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Outline





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Coherent Detection

!"#$%& ( ")*!+ , + %,-./ +

01 + %23+0( "#$%& ")*-./$ 01#2 1)*3% ( 0)#$%& 4 ))*3 &

All linear distortions (Dispersion, PMD, PDL) can

theoretically be fully compensated. Nonlineardistortion can be partially compensated

Coherently

ReceivedElectrical Signal

~

Electric Field

Vector ofOptical Signal

LinearSystem

Signal Amplitude Signal Phase

90oHybrid


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# Limited to receivers.

MotivationAsynchronous Sampling (by MDI)

(Asynchronous sampling)

Clean Noise CD

PMD Crosstalk All

Input

DataDelay

Sampling

On-Off-Keying Data

Unique impairment pattern!multiple impairments monitoring


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Router

ONE

ONE

Router

Router

Optical Network

End Customer

Re-route or feed backinformation tocontrol the ONE

Trained receiversto

automatically identifyimpairments

ONE

Send error

signals

Fiber link withvarious impairments

Router

Self-Managed Optical Networks

! Monitored information can be sent to the network controller andoptical network elements to rapidly reroute the data information

X. Wu et al, J. Lightwave Technol. 27 (16), 2009.


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Concept - ANNs Trained w/ Eye Diagram Parameters

! It is obvious that different impairment combinations producedistinct features in the eye diagrams! The input parameters for training are derived from eye diagrams

% Q-factor, eye-closure, jitter, and crossing amplitude! The controlled impairments are used as outputs for training

Tx

Rx

OSNR = 36 dBCD = 0DGD = 0



OSNR = 28 dB

CD = 60 ps/nmDGD = 0

OSNR = 28 dB

CD = 0DGD = 10 ps

OSNR = 28 dB

CD = 60 ps/nmDGD = 10 psF

iberLink



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Artificial Neural Networks

Advantages of ANN Approach

! Efficient identification and isolation of multiple impairments! Enhanced monitoring range and sensitivity! Simple and fast processing of the monitored information! Format transparent



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Crossing Amp.

OSNRCD

DGD

3-Layer ANN Model12 Hidden Neurons

64 Testing Samples

Q-factor

Closure

Jitter

OSNR

CD

DGD

3-Layer ANN Model

12 Hidden Neurons

Conjugant Gradient

Training

125 Samples

Q-factor

Closure

Jitter

Crossing Amp.

40-Gb/s RZ-OOK testing results

40-Gb/s RZ-DPSK testing results

Training Errors for OOK and DPSK Systems

Block Diagrams for ANN Training and Testing

X. Wu, ECOC 2008

OSNR/CD/PMD Identifications using ANNs


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OSNR=36,

CD=0, DGD=0

OSNR = 16, CD=0,

DGD = 0

OSNR = 36, CD=60,

DGD = 0

OSNR = 36, CD=0,

DGD = 10

OSNR = 20, CD=45,

DGD = 7.5

OSNR = 16, CD=60,

DGD = 10

Concept - ANNs Trained w/ Delay-Tap Plot Parameters

! It is obvious that different impairment combinations producedistinct features in the delay-tap plots

X. Wu et al, ECOC 2009, paper P3.04.


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