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All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
40Gb/s & 100Gb/s Transport in the WAN
Dr. Olga VassilievaFujitsu Laboratories of America, Inc.
Richardson, Texas
1 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Outline
Introduction
Challenges of 40Gbps transmission
Modulation formats for 40Gbps
Advanced optical technologies enabling 40Gbps
From 40Gbps to 100+Gbps
Summary
2 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Introduction
Today’s networks deploy 2.5Gbps and 10Gbps line rates
Networks will migrate to 40Gbps (and in the future to 100Gbps) per wavelength
High demand for transmission capacityHigher rate client interfaces
Technologies to support 40Gbps transmissionAdvanced modulation formatTunable Chromatic Dispersion Compensator (TDC)Tunable lasers
40Gbps networks must co-exist with today’s networks
3 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Supporting 40Gbps Transmission
Same transmission quality as 10Gbps systemsChallenges associated with 40Gbps solution:• OSNR requirement increases by 6 dB• Chromatic dispersion tolerance decreases (1/16-th of 10G system) • PMD tolerance decreases (1/4-th of 10G system)
Same network connectivity as 10GbpsChallenges:• Sensitivity to OADM filtering increases
Example of optical spectra40 Gbit/s NRZ signal
80 GHz
10 Gbit/s NRZ signal
20 GHz
4 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Increasing Channel Capacitychannel spacing
λ1 λ2 λ3
10 Gbit/sOptical spectrumPo
wer
λ
Pow
er
40 Gbit/sOptical spectrum
crosstalk
λ
Pow
er
40 Gbit/sOptical spectrum
Transmittance of optical filter
λ
cut off
Solution: New Modulation Formats with improved spectral efficiency.
Solution: New Modulation Solution: New Modulation Formats with improved Formats with improved spectral efficiency. spectral efficiency.
3 channels at 10 Gbit/sChannel spacing: ∆λ
3 channels at 40 Gbit/sChannel spacing: ∆λ(same)
Crosstalk between channels
Spectrum degradation due to cascaded ROADM filter devices
5 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Light Properties to Modulate
IntensityIntensity Phase (Frequency)Phase (Frequency)
PolarizationPolarization
Modulate one or more light propertiesIntensity modulation (on-off keying):• Widely used modulation technique for up to 10Gbps transmission
• Easy to modulate and easy to detect
Phase modulation:• Well known technique but was not used in optical communications
• Detection is more difficult compared to on-off keying
Polarization modulation:• Relatively new technique
• Detection is difficult
6 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Non Return-to-Zero (NRZ)
Transmitter
outLD
43 Gb/sData
MZM
Intensity
Phaseπ/20 time
1 1 0 1 0
−π/2
Eye diagram
NRZ
Optical spectrum
Intensity modulation format Widely used at 10Gb/sSimplest Tx and Rx configurationThe optical spectrum has a carrierNRZ has medium width optical spectrum
7 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Carrier-Suppressed Return-To-Zero (CS-RZ)
Intensity modulation formatCS-RZ Tx requires additional clock modulationPulse train has RZ shape with alternate πphase shifts between consecutive bit slotsThe optical spectrum has a suppressed carrierHigh tolerance to non-linear effectsHigher receiver sensitivity than NRZ
outLD
43 Gb/sData
Transmitter
21.5 GHzClock
21.5 GHzClock
Intensity
Phaseπ
0 time
1 1 0 1 0
MZM
Eye diagram
NRZ
CS-RZ
Optical spectrum
Y. Miyamoto et al., in Proc. OAA’99, vol. PdP4, 1999.
Intensity
Phaseπ/2
0time
1 1 0 1 0
−π/2
8 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
out
LPF
LD
43 Gb/sData
Pre-coder
43 Gb/sData
Pre-coder
LPF
Eye diagram
MZM
Duobinary
Transmitter
Intensity
Phaseπ
0 time
1 1 0 1 0
Optical spectrum
Duobinary Modulation Format
Intensity modulation formatComplicated Tx design:
Requires data pre-coder and low pass filter (LPF)
Pulse train has NRZ shape with some residual light within “0” symbolsNarrow optical spectrum
Increased spectral efficiency and Large chromatic dispersion tolerance
Poor receiver sensitivity: 3 dB worse than NRZPoor non-linear tolerance
K. Yonenaga et al., J. Lightwave Technol., vol. 15, No. 8, pp. 1530-1537, 1997.
9 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
LD
43 Gb/sData
43 GHz or21.5 GHz
Clock
43 GHz or 21.5 GHz
Clock
Pre-coder
PM
TransmitterEye diagram
DPSK
RZ-DPSK
Optical spectrum
Intensity
Phaseπ
0 time
1 1 0 1 0
Intensity
Phaseπ
0 time
1 1 0 1 0
Return-to-Zero Differential Phase Shift Keying (RZ-DPSK)
Phase modulation format Tx requires two modulators:
Phase Modulator (PM) and Intensity Modulator (IM)
Pulse train has RZ shape3 dB Rx sensitivity advantage over NRZHigh tolerance to non-linear effects
Y. Miyano et al., in Proc. OECC’2000, vol. 14D3-3, 2000.
10 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Transmitter
outLD
21.5 Gb/sData
21.5 GHz or 10.75 GHz
Clock
21.5 GHz or 10.75 GHz
Clock
Pre-coder
π/2π/2 PM
PM
21.5 Gb/sData
Pre-coder
DQPSKRZ-DQPSK
Eye diagramOptical spectrum
7π/4
3π/4
Intensity
Phase5π/4
π/4 time
1 1 0 1 0
Intensity
Phase
time
1 1 0 1 07π/4
3π/45π/4
π/4
Return-to-Zero Differential QuadraturePhase Shift Keying (RZ-DQPSK)
Four level phase modulation Reduced line rate by 50% compared to DPSK:
increased spectral efficiency, PMD and Chromatic dispersion tolerance
More complex transmitter design:two phase modulators and one intensity modulator
Pulse train has RZ shapeOptical spectrum is narrow Has ~3 dB Rx sensitivity advantage over NRZ
R.A. Griffin et al., in Proc. OFC’2002, WX6, 2002.
11 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Cumulative transmission window
・・・・・・・・OADM OADM OADMPo
wer
(20
dB/)
f
T
f
T
f
T
Pow
er (2
0 dB
/)
Tolerance to OADM Concatenation
Before filteringSignal spectrum
After 24 OADM nodesSignal spectrum
Frequency (50GHz/) Frequency (50GHz/)
RZ-DPSK
RZ-DQPSK
Before filtering After 24 OADMs
CS-RZ
After 16 OADMs
NRZ
12 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Optical Noise Tolerance of 40Gbps Signals
Simulation results
Duobinary
NRZ
RZ-DPSKRZ-DQPSK
4.5 dB
7 dB
Both RZ-DPSK and RZ-DQPSK have high OSNR tolerance
13 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
PMD Tolerance of 40Gbps Signals
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30 35DGD (ps)
Q p
enal
ty (d
B)
Simulation results
RZ-DQPSKRZ-DPSKNRZ
43 Gbit/s
RZ-DPSK exhibits two times larger PMD tolerance than NRZ due to RZ pulse carvingRZ-DPQSK exhibits even larger tolerance due to halved symbol-rate
14 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Optical Nonlinearity Tolerance of 40Gbps Signals
Simulation results: SMF 4 spans x 50 km
-0.50
0.51
1.52
2.53
3.54
4.5
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6
Fiber input power (dBm/ch)
Q p
enal
ty (d
B)
DuobinaryNRZRZ-DPSKCS-RZRZ-DQPSK
NRZ
RZ-DPSKRZ-DQPSK
CS-RZ
Duobinary
Advanced modulation formats such as CS-RZ, RZ-DPSK and RZ-DQPSK show high tolerance to non-linear effects
15 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Chromatic Dispersion Tolerance
Optical duobinary
NRZCS-RZ
RZ-DQPSKCSRZ-DPSK
Q-p
enal
ty (d
B)
0 100 200 300-200 -100-300Residual dispersion (ps/nm)
0
5
1
2
3
4
-1
-2
RZ-DQPSK and Duobinary show CD high tolerance
16 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
40 Gbps Modulation Formats
medium
poor
medium
poor
medium medium
very good
medium
good
medium
good
good
good
good
good
Optical nonlinearity tolerance
Optical noise tolerance
: Advantage
PMD tolerance
: Disadvantage
NRZ
Optical spectra
Chromatic dispersion tolerance
MZI outRZ-DPSK
Tx out
“1”→ ∆Phase= π“0”→ ∆Phase= 0
OADM filtering tolerance
RZ-DQPSKMZI outTx out
4 values are mapped to ∆phase 0, π/2, π, 3π/2
good(in linear regime)
medium
poor
good
very poor
Duobinary
good
medium
medium
medium
medium
CS-RZ
Frequency (GHz) Frequency (GHz) Frequency (GHz) Frequency (GHz) Frequency (GHz)
RZ-DQPSK is attractive in many aspects for high bit-rate transmission
17 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
40Gbps RZ-DQPSK
RZ-DQPSK is the best modulation format to enable 40Gbps transmission
Superior filtering tolerance• Multiple passes through ROADMs
Superior CD tolerance• Can support 40Gbps WDM transmission over existing networks
Superior PMD tolerance and OSNR performance• Longer transmission spans, fewer regeneration sites and increased number of ROADM nodes per network
18 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Advanced Technologies to Support 40Gbps Transmission
modulator
Tunable laser
Optical transmitter
CDRVDC
Optical receiverTransmission line
FECPDOptical amp
Device Characteristic
Tunable laser source Narrow spectral linewidth & full-band tunability
Modulator Generates 40Gbps signal
Variable dispersion compensator (VDC)
Operates at any wavelength in entire band withsmall pass-band effects
High-speed electronic devices Devices for modulator drivers, preamp, and CDR (clock and data recovery)
High performance error correction technology
Extended transmission distance with minimal bit rate increase
19 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
LiNbO3 Modulators for 40Gb/s
40 Gb/s low drive voltage DQPSK LN optical modulatorUltra low 4.0 V drive voltage25 GHz bandwidthCompact sizeIntegration of phase modulators
RZ-DQPSK
DATA CLOCK
PM
PMπ/2
20 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
40Gb/s RZ-DQPSK Transceiver Module
10 12 14 16 18 20 22 24BE
R
Optical SNR (dB)
10-4
10-10
10-8
10-5
10-9
10-11
10-12
10-7
10-6
10-3
10-2
RZ-DQPSKtransceiver
NRZ transceiver
4.5 dB
Modulation format: RZ-DQPSKC- and L-band fully tunableMulti rate: 43 Gb/s, 44.6 Gb/sSFI-5, 300pin MSA interfaceSize: 320mm x 110mm x 40mmLow power consumption: 35 W
4.5 dB noise tolerance improvement from NRZ format
2.8x transmission distance
21 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
40Gb/s RZ-DQPSK Transceiver Performance
0.0
0.5
1.0
1.5
2.0
2.5
0 500 1000 1500
Transmission distance estimated by PMD tolerance [km] (in case of PMD coefficient 0.2 ps/ km)
DQPSK:810 km
about 8 times
Binary modulation:100 km
DQPSKMeasuredBinary
modulation CalculatedMeasured
Calculated
Degradation of signal quality [dB]
Deg
rada
tion
of s
igna
l qua
lity
[dB
]
Transmission reach limited by PMD was found 8 times better than that of standard binary modulation
Longer spans and fewer regeneration sites
22 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Variable Dispersion Compensation for 40Gbps
x
z
y
Optical circulator
Line-focus lens
Collimatinglens
Glass plate
Cylindrical lens 1
Cylindricallens 2
Transmissiongrating
3-Dmirror
Virtually ImagedPhased Array Component
Virtually ImagedVirtually ImagedPhased Array Phased Array ComponentComponent
Chromatic dispersion in 40Gbps systems
More severe dispersion tolerance• ~ 50 ps/nm • 1/16 of 10G systems
Chromatic dispersion changes with temperature
• ~60 ps/nm @ 600 km, 50°C change
Advantages of available Variable Dispersion Compensation
Replaces “menu” of fixed DCMHigh tunable dispersion resolution:1 ps/nmLarge variable dispersion range:± 800 ps/nmNo penalty due to fiber nonlinear effect
23 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Deployment Strategies of 40Gbps
Green field deploymentDeployment of new 40Gbps DWDM systems
Upgrade of already installed 10Gbps DWDM systems*Add 40Gbps line cards to existing 10Gbps DWDMUtilize the same existing transmission infrastructure• Same fibers• Same dispersion compensating modules (DCM)• Same optical amplifiers• Same OADM nodes (same OADM filtering properties)
R. Fiorone et al., in Proc. OCOC’2004, Th.2.5.4, 2004.
24 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Upgrade of Existing 10Gbps Networks
Migration to 40Gbps is very simple thanks to currently developed 40Gbps technologies such as:
New spectrally efficient modulation formats (i.e. DQPSK)Variable dispersion compensation
Simply add 40Gbps line cards to existing 10Gbps networksIncrease transmission capacity w/o installation of new networksNo changes to existing infrastructures – cost savings!No impact on 10Gbps signals
10Gbps and 40Gbps signals canco-exist in the same network !
25 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Transmission
IEEE 802.3 HSSG is considering multiple approachesShort haul connections• Typically 300-1000 meters for inter-switch links in data centers.• Current proposals: 4x CWDM, 5x, 10x parallel
Medium-range interface ~ 10 Km, 40Km• Current Proposals: 4x, 5x parallel, 1x serial
Question: How to transport 100GE in DWDM networks?
Transport on multiple wavelengths
Requires synchronization of wavelengths due to differential propagation delayManage a band of wavelengthsSimpler Tx/Rx, but low fiber
Parallel SerialTransport on single wavelength
Complex Tx/RxHigher spectral efficiencyHigher total transport capacity over a WDM systemTransmission impairments
utilization
26 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Transmission Impairments at 100Gbps
Transmission impairments are very severe at 100G:Chromatic dispersion tolerance decreases (1/100-th of 10Gb/s system) PMD tolerance decreases (1/10-th of 10G system)OSNR requirement increases by 10dB
Today’s networks are mostly designed for 100 GHz ITU gridSensitivity to OADM filtering increases
Counter-measuresAdvanced multi-level modulation formats• Low symbol rate
Adaptive CD compensationForward error correction (FEC) Coherent detection• PMD and CD tolerance can be further improved
27 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Serial Transmission
How to transport 100GE serially in DWDM networks?
10G 40G 160G Data Rate (b/s)
bit/s
ymbo
l
(RZ/NRZ)10G elec.
1
2
4
QPSK20G elec.
(RZ/NRZ) 40G elec.
(e.g. POLMUX QPSK)10G elec.
(A) Increase data rate OR(B) Multi-level modulation ( X bits per symbol)
28 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Serial Transmission (OTDM)
Various 100Gbps serial optical transmission experiments have been performed:
(1) Optical time division multiplexing (OTDM) (480km DMF)Pros: Low speed electronics
Cons: Requires short-pulse laser sourceTransmitter tends to be bulky and expensiveComplex signal processing at the transmitter and receiver Operation on 100GHz ITU grid is not feasible
R. Derksen et al., in Proc. OFC’2006, PDP37, 2006.
Short-pulse laser
MZM
OTDM-MUX 8x12.5 -> 100 Gb/s
Rx
w/1:2 DEMUX
100 Gb/s NRZ
8x 12.5 Gb/sdata
MZM
MZM
29 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Serial Transmission (ETDM)
(2) Electrical time division multiplexing (ETDM)107 Gbps NRZ or Duobinary transmission100G electronics is not a mature technologyCons: Bandwidth limitation of electro-optical modulator and receiver
• Operation on 100GHz ITU grid is not feasible
LD MZM
100 Gb/s data
Rx
w/1:2 OTDM demux
100 Gb/s NRZ or Duobinary
2:1 mux2x 50 Gb/s data
P.J. Winzer et al., in Proc. OCOC’2005, PD paper Th4.1.1, 2005.
C.R. Doerr et al., in Proc. OCOC’2005, PD paper Th4.2.1, 2005.
30 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Serial Transmission (DQPSK)
(3) DQPSK is a good candidates for 100+Gbps transmissionPros: • Symbol rate 50Gbaud/s• Lower speed electronics (50Gbps)• Relaxed CD, PMD and OSNR tolerance• Operation on 100GHz ITU grid is feasible
Cons: • Higher complexity of transmitter/receiver
PM
PMLD
2x 50 Gb/s data
50 GbaudDQPSK
O/EO/EDemodulator
2x 50 Gb/s O/E
M. Daikoku et. al, OFC’2006, PDP36.
31 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Serial Transmission (POLMUX DQPSK)
(4) POLMUX DQPSK is another candidate• Low speed electronics (25Gbps)• Operation on 100GHz ITU grid is feasible • PMD limited reach and CD tolerance increases due to doubled symbol duration
PM
PMPM
PM
PBSRZ mod PBCLD
V
H
V
H
I
QI
Q
2x 25 Gb/s el. driver
2pol x 25 Gbaud
Polarization mux
2x 25 Gb/s el. driver
Optical diverse coherent receiver*
LD
90o
Hybrid
90o
Hybrid
O/E ADCO/E ADC
O/E ADCO/E ADC
4x 25 Gb/s O/EPBS
Pro
cess
orD
igita
l Sig
nal
(A) 100Gb/s
C.R.S. Fludger et. al, OFC’2007, PDP22.
O/EO/E
O/EO/E
Delay Interferometer
DI
DIV
H
4x 44 Gb/s
PBSPolarization alignment
Direct detection receiverPM
PMPM
PM
PBSRZ mod PBCLD
V
H
V
H
I
QI
Q
2x 44 Gb/s el. driver
2pol x 44 Gbaud
Polarization mux
2x 44 Gb/s el. driver
(B) 160Gb/s
A.H. Gnauck et. al, OCOC’2006, Th4.1.2.
32 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Champion Experiments
When Experiment Distance Company PaperECOC 2005 107Gb/s Duobinary ETDM Tx, OTDM Rx - Alcatel-Lucent Th.4.1.1
ECOC 2005 107Gb/s NRZ ETDM Tx and OTDM Rx - Alcatel-Lucent Th.4.2.1
ECOC 2006 10x107Gb/s ETDM NRZ OTDM Rx 1000 km Alcatel-Lucent Tu.1.5.1.
ECOC 2006 10x107Gb/s RZ-DQPSK transmission 2000 km Alcatel-Lucent Th.4.1.3
OFC 2007 10x107 Gb/s NRZ transmission 480 km Alcatel-Lucent PDP23
OFC 2007 10x111Gb/s PDM-RZ-DQPSK 2,375 km CoreOptics-Siemens PDP22
OFC 2006 10x107 Gb/s NRZ transmission 400 km Alcatel-Lucent PDP32
OFC 2006 100Gb/s DQPSK 50 km KDDI-NICT-Sumitomo PDP36
OFC 2006 100Gb/s NRZ ETDM Rx 480 km HHI-Siemens-Micram PDP37
ECOC 2006 140x111Gb/s PDM-CSRZ-DQPSK 160 km NTT Th.4.1.1
OFC 2007 10x107 Gb/s NRZ-DQPSK transmission 1,200 km Alcatel-Lucent PDP24
OFC 2007 204x111Gb/s PDM-CSRZ-DQPSK 240 km NTT PDP20
33 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
100+ Gbps Transmission
100+ Gbps transmission is possible with:Multi-level modulation (I.e. QPSK)Polarization multiplexingAdaptive CD compensationFECCoherent detection• PMD and CD tolerance can be further improved
Advantages of using QPSK:Low speed electronics Relaxed CD, PMD and OSNR tolerance due to low symbol rateOperation on 100GHz ITU grid is feasible due to narrower opticalspectrum• Compatibility with existing networks
34 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.
Summary
Discussed 40Gbps enabling technologiesAdvanced modulation formatsTunable lasers Variable Chromatic Dispersion Compensator
RZ-DQPSK has the best CD, PMD performance and filtering tolerance
Universal solution to 40Gbps Metro/LH applications
40Gbps channels can be added to 10Gbps infrastructures without any change of existing networks
Transition from 40G to 100+G is possible with DQPSK
Thank you!Thank you!Thank you!
35 All Rights Reserved, ©2007 Fujitsu Laboratories of America, Inc.