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7/25/2019 Tutorial Optical Transmission Systems Peter J Winzer
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COPYRIGHT 2015 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Optic Communication Systems
For Non-Optical Communications EngineersPeter J. WinzerBell Labs, Alcatel-Lucent, USA
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ACKNOWLEDGMENT
Bell Labs
S.ChandrasekharA.R.ChraplyvyR.-J.EssiambreN.K.FontaineG.J.FoschiniH.KogelnikG.KramerA.LevenX.Liu
S.RandelG.RaybonR.RyfR.W.Tkach
AND MANY OTHERS
Univ. Tel Aviv
Univ. LAquilaC.AntonelliR.DarA.MecozziM.Shtaif
Politecnico di Torino
P.Poggiolini
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OVERVIEW
The role of optics in data networks
Linear and nonlinear impairments in optical networks
Optical modulation and detction techniques
Optical multiplexing techniques
Spatial multiplexing in optical communications
(MIMO and MIMO-SDM security)
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1
The role of opticsin data networks
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MASSIVE TRAFFIC GROWTHMULTI-MEDIA & MACHINE-TO-MACHINE APPLICATIONS
HiDef Video Communication Panasonics LifeWall
1995 2000 2005 2010
2 dB / year(58%/year)
10 Gb/s
100 Gb/s
1 Tb/s
10 Tb/s
US data network traffic
100 Tb/s
60% 10 log10(1.6) dB 2 dB
[R.W.Tkach, Bell Labs Tech. J., 2010]
3D manipulation
zspace.com
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Amdahls rule of thumb
1 Floating point operation (Flop) triggers ~1 Byte of transport
100 TFlops
10 TFlops
1 TFlops
100 GFlops
10 GFlops
1 GFlops
1995 2000 2005 2010
2.7 dB / year(86%/year)
2 dB / year(58%/year)
10 Gb/s
100 Gb/s
1 Tb/s
10 Tb/s
US data network traffic
Top 500 Supercomputers 100 Tb/s
60% 10 log10(1.6) dB 2 dB
http://www.circuitboards1.com
MASSIVE TRAFFIC GROWTHMULTI-MEDIA & MACHINE-TO-MACHINE APPLICATIONS
[P.J.Winzer, Proc. ECOC, 2010]
Cloud services turn the network into a giant multi-processor interface
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TRAFFIC GROWTH VARIATIONS: 20% TO 90%DEPENDING ON APPLICATION AND GEOGRAPHY
IEEE 802.3 Industry Connections Ethernet Bandwidth Assessment, http://www.ieee802.org/3/ad_hoc/bwa/BWA_Report.pdfMetro Network Traffic Growth, Bell Labs Strategic White Paper, http://resources.alcatel-lucent.com/asset/171568M. Nowell, Cisco Visual Networking Index; 20102015, http://www.ieee802.org/3/ad_hoc/bwa/public/sep11/nowell_01_0911.pdf Cisco Visual Networking Index: Forecast and Methodology, 20132018, http://www.cisco.com
[P. J. Winzer, Bell Labs Tech. J., 2014]
http://www.ieee802.org/3/ad_hoc/bwa/BWA_Report.pdfhttp://resources.alcatel-lucent.com/asset/171568http://www.ieee802.org/3/ad_hoc/bwa/public/sep11/nowell_01_0911.pdfhttp://www.cisco.com/c/en/us/solutions/collateral/service-provider/ip-ngn-ip-next-generation-network/white_paper_c11-481360.pdfhttp://www.cisco.com/c/en/us/solutions/collateral/service-provider/ip-ngn-ip-next-generation-network/white_paper_c11-481360.pdfhttp://www.cisco.com/c/en/us/solutions/collateral/service-provider/ip-ngn-ip-next-generation-network/white_paper_c11-481360.pdfhttp://www.cisco.com/c/en/us/solutions/collateral/service-provider/ip-ngn-ip-next-generation-network/white_paper_c11-481360.pdfhttp://www.ieee802.org/3/ad_hoc/bwa/public/sep11/nowell_01_0911.pdfhttp://www.ieee802.org/3/ad_hoc/bwa/public/sep11/nowell_01_0911.pdfhttp://www.ieee802.org/3/ad_hoc/bwa/public/sep11/nowell_01_0911.pdfhttp://resources.alcatel-lucent.com/asset/171568http://resources.alcatel-lucent.com/asset/171568http://resources.alcatel-lucent.com/asset/171568http://resources.alcatel-lucent.com/asset/171568http://www.ieee802.org/3/ad_hoc/bwa/BWA_Report.pdfhttp://www.ieee802.org/3/ad_hoc/bwa/BWA_Report.pdfhttp://www.ieee802.org/3/ad_hoc/bwa/BWA_Report.pdf7/25/2019 Tutorial Optical Transmission Systems Peter J Winzer
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DATA NETWORKING INFRASTRUCTUREOPTICAL COMMUNICATIONS EVERYWHERE
Core
Access
LAN
Satellites
Data center
SwitchingTransport
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WHY OPTICAL COMMUNICATIONS?
1 0 1 1 0 1 0 1 1 0
TX RXMetric: Maximum transmission distance that can be
bridged before digital regeneration becomes necessary.
High data rates
and
long distances
Fiber to the home
(FTTH)
Alcatel-Lucents1830 PSS
Reg
eneration-freetra
nsmissiondistanc
e
Aggregate link capacity
[P. J. Winzer et al., Proc. IEEE 94, 952-985 (2006)]
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WHY OPTICAL COMMUNICATIONS?REASON #1: LARGE NARROW BANDWIDTHS
1 kHz 1 MHz 1 GHz 1 THz 1 PHz
Frequency / wavelength of the electromagnetic field
VLF LF MF HF
1 km 1 m 1 mm 1 mm
VHF UHF SHF EHF
V
isible
Light
h
=
kT
~ 5 GHz
C L
At 200 THz (1.5mm) carrier frequency
Low-loss fiber
Efficient sources & detectors
Low-noise amplifiers (EDFAs)
5 50 THz of channel bandwidth
is still narrowbandat 200 THz(~a few % relative bandwidth)Thats where most digital radio happens
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WHY OPTICAL COMMUNICATIONS?REASON #2: VERY LOW PROPAGATION LOSSES
Loss[dB/km]
Accurate pointing needed
(~ mrad @ kHz vibrations)
K. H. Kudielka et al.,
Proc. IEEE Phased Array
Symposium, Boston, 419 (1996)
Attenuation of glass
Today: < 0.2 dB / km
(RF coax: ~ 100x to 1000x more loss)
Divergence angle ~ l/D
PRX~ PTXDTXDRX/ l222
E.g., 200 THz instead of 20 GHz
108x higher antenna gain (80dB)
Divergence in free space
D
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TELECOMMUNICATIONS BEFORE FIBER-OPTICSAT&TS LONG-HAUL BUSINESS
Technology Designation YearVoice circuits
per channel
2-way
channels
Repeater
distance
Total 2-way
voice circuits
Coax
L-1 1941 600 4 8 miles 2400
L-3 1950 1,860 6 4 miles 11,160
L-4 1967 3,600 10 2 miles 36,000
L-5E 1975 13,200 11 1 mile 145,200
Microwave
Relay
TD-2 (4 GHz) 1969 1,200 12 26 miles 14,400
TH-1 (6 GHz) 1961 1,860 8 26 miles 14,880
AR6A (6 GHz) 1981 4,000 8 26 miles 32,000
mm-
WaveguideWT4 (trial) 1975 4,032 57 25 miles 230,000
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Courtesy: H. Kogelnik
FIBER VS. COPPER - A CLEAR BUSINESS CASE
For 6x less in cable diameter,and 23x less in weight,and 25x longer repeater spacing,you got 156x more capacity!
Ca. 1977
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OPTICAL NETWORKS: WORKHORSE OF THE INTERNET
Lineinterface(e.g., 100 Gbit/s)
Router
Optical network
Reconfigurable opticaladd/drop multiplexer
(ROADM)
Clientinterface(e.g., 4 x 25 Gbit/s)
WDMsystem(e.g., 80 x 100 Gbit/s)
Increaseper-wavelength interface rateIncrease aggregateper-fiber capacityIncrease network flexibility
Spectral efficiency (SE) in [b/s/Hz]:
SE = per-channel bit rate / WDM spacing
Tx Rx
~ 5 THz bandwidth ~ 100 km of fiber
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HIGH-SPEED OPTICAL INTERFACESWHY A TERABIT IS CHALLENGING BUT NEEDED
1986 1990 1994 1998 2002 2006
10
100
1
10
100
SerialInterfaceRat
esandWDMCapacit
ies
Gb/s
Tb/s
2010 2014 2018
1
2022200G optical line interfacesare now available
Router interfacescaling has merged with transport rates
Router port aggregationno longer possible[P. J. Winzer, IEEE Comm. Mag. 26-30 (2010)]
Network processors available at 400G
1-port 100GigE
?
!
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HIGH-CAPACITY WDM SYSTEMSWHEN WILL WE NEED FASTER INTERFACES ?
20% 40% 60% 80%
400 Gb/s 2018 2014 2013 2012
1 Tb/s 2023 2017 2015 2014
10 Tb/s 2035 2024 2020 2018
(Simple extrapolation of higher interface needs)
Fact: Leading-edge providers started installing 100G interfaces in 2010.Question: When will such providers want higher-rate interfaces?
Assumedtrafficgrowth rate
Assumedinterface raterequirement
Extrapolated availability requirementfor higher-speed interfaces
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HIGH-CAPACITY WDM SYSTEMSCOMMERCIAL CAPACITY SATURATION AT ~ 50 TB/S
1986 1990 1994 1998 2002 2006
10
100
1
10
100
SerialInterfaceRat
esandWDMCapacit
ies
Gb/s
Tb/s
2010 2014 2018
1
2022
WDM capacity scaling has slowed from ~100%/year to ~20%/year in 2000
WDM systems available up to ~10 to 20 Tb/s
[P. J. Winzer, IEEE Comm. Mag. 26-30 (2010)]
?
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HIGH-CAPACITY WDM SYSTEMSWHEN WILL WE NEED FASTER INTERFACES ?
(Simple extrapolation of higher WDM capacity needs)
Fact: Leading-edge providers started installing 10T WDM systems in 2010.Question: When will such providers want higher-capacity systems?
AssumedTrafficgrowth rate
AssumedWDM capacityrequirement
Extrapolated availability requirementfor higher-capacity systems
20% 40% 60% 80%
50 Tb/s 2019 2015 2013 2012
200 Tb/s 2026 2019 2016 2015
1 Pb/s 2035 2024 2020 2018
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HIGH-CAPACITY WDM SYSTEMSCOMMERCIAL CAPACITY SATURATION AT ~ 50 TB/S
1986 1990 1994 1998 2002 2006
10
100
1
10
100
SerialInterfaceRat
esandWDMCapacit
ies
Gb/s
Tb/s
2010 2014 2018
1
2022
WDM capacity scaling has slowed from ~100%/year to ~20%/year in 2000
WDM systems available up to ~10 to 20 Tb/s
[P. J. Winzer, IEEE Comm. Mag. 26-30 (2010)]
?
?
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2Impairments in opticalnetworks
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NOISE FROM OPTICAL AMPLIFIERSAMPLIFIED SPONTANEOUS EMISSION (ASE)
Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Lower bound on noise dictated by quantum mechanics
Optical signal-to-noise ratio (OSNR):
RXTX
Amplified spontaneous emission (ASE)
Optical signal power
Optical noise power
[R.-J. Essiambre et al., J. Lightwave Technol. (2010)]
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NOISE FROM OPTICAL AMPLIFIERSAMPLIFIED SPONTANEOUS EMISSION (ASE)
Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Lower bound on noise dictated by quantum mechanics
Optical signal-to-noise ratio (OSNR):
RXTX
Amplified spontaneous emission (ASE)
Optical signal power
Optical noise power
G amplifier gain = span lossNspan number of spans
Span length 100km 50km
Span loss (=G) 20dB 10dB
Spans Nspan 2 Nspan
Total noise 100 Nspan 20 Nspan
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NOISE FROM OPTICAL AMPLIFIERSAMPLIFIED SPONTANEOUS EMISSION (ASE)
Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Lower bound on noise dictated by quantum mechanics
Optical signal-to-noise ratio (OSNR):
RXTX
Amplified spontaneous emission (ASE)
Optical signal power
Optical noise power
[R.-J. Essiambre et al., J. Lightwave Technol. (2010)]
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FIBER NONLINEARITIESTHE ULTIMATE LIMIT OF FIBER TRANSMISSION Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Lower bound on noise dictated by quantum mechanics
Increase signal power for better (O)SNR:
Fiber nonlinearities
(within a signal, between WDM signals, between signal and noise)
Signal power
(Optical) noise power
Core diam. ~8 mmMegawatt / cm2optical intensities
n = n0+n1Popt+ (Kerr effect)
Leads to nonlinear distortionsover hundreds of kilometers
A A ejznzA ejzn z ejzn P z0 1 opt
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FIBER NONLINEARITIESTHE ULTIMATE LIMIT OF FIBER TRANSMISSION Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Lower bound on noise dictated by quantum mechanics
Increase signal power for better (O)SNR:
Fiber nonlinearities
(within a signal, between WDM signals, between signal and noise)
RXTX
Amplified spontaneous emission (ASE)
Signal power
(Optical) noise power
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CHROMATIC DISPERSION AND PMD
Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Signal-distortions
Fiber nonlinearity
Chromatic dispersion, polarization-mode dispersion
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CONCATENATED FILTERING IN OPTICAL NETWORKS
Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Signal-distortions
Fiber non-linearity
Chromatic dispersion, polarization-mode dispersion
Optical filter concatenation
l1
lN
DEMUX MUX
Drop AddWDM multiplexer
WDM demultiplexer
l1
lN
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CROSSTALK IN OPTICAL NETWORKS
Fiber and optical component loss
Noise from in-line amplification (EDFA, Raman); proportional to gain G Signal-distortions
Fiber non-linearity
Chromatic dispersion, polarization-mode dispersion
Optical filter concatenation
Crosstalk (WDM, inband)
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OPTICAL FIBER TRANSMISSION
Optical field propagating in the fibers transverse mode
(Nonlinear Schrdinger Equation)+ N
ROADM Reconfigurable optical add/drop multiplexer
FiberNonlinearity
FilteringEffects
Chromatic Dispersion
Optical Filtering (ROADMs)
Spontaneous emission from
in-line optical amplifiers
Noise
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Simulation steps
Step size DzDz
0 2 3 4 5 6 7 81 Distance
SPLIT-STEP FOURIER TRANSFORM METHOD
NUMERICAL SOLUTION OF FIBER PROPAGATIONConsider short pieces of fiber (dispersion only, nonlinearity only)
Alternate between simple solution in t and f
Nonlinearity (but no dispersion)
Dispersion (but no nonlinearity)
Courtesy: Pierluigi Poggiolini
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Courtesy: Pierluigi Poggiolini
Courtesy: Pierluigi Poggiolini
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Courtesy: Pierluigi Poggiolini
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DISPERSION-MANAGED SYSTEMS
MANAGING NONLINEARITY WAS REALLY HARD
0.01
0.1
1
10
Spectralefficiency
perpolarization[b/s/
Hz]
1990 1994 1998 2002 2006
Year
2010
Laser & filter stability
x-pol
y-pol
x-pol
y-pol
Modulation
PDM
~1 dB/year
Detection
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Courtesy: Pierluigi Poggiolini
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y g gg
FINDING THE FACTOR
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FINDING THE FACTOR
Optics Express, 16335 (2014)
J. Lightwave Technology (2015)
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3Modulation inoptical communications
HIGH CAPACITY WDM SYSTEMS
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HIGH-CAPACITY WDM SYSTEMSCOMMERCIAL CAPACITY SATURATION AT ~ 50 TB/S
1986 1990 1994 1998 2002 2006
10
100
1
10
100
SerialInterfaceRa
tesandWDMCapaci
ties
Gb/s
Tb/s
2010 2014 2018
1
2022
WDM capacity scaling has slowed from ~100%/year to ~20%/year in 2000
WDM systems available up to ~10 to 20 Tb/s
[P. J. Winzer, IEEE Comm. Mag. 26-30 (2010)]
?
?
THE COMMUNICATION ENGINEERS TOOLKIT
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THE COMMUNICATION ENGINEERS TOOLKIT
5 DIMENSIONS OF AN ELECTRO-MAGNETIC WAVE
Polarization
Time Quadrature
Modulation of the field in
Frequency
Space
Same 5 dimensions across communications technologies(Wireless, DSL, Optics, )
USING THE FIVE PHYSICAL DIMENSIONS
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USING THE FIVE PHYSICAL DIMENSIONSAN OPTICAL COMMUNICATIONS POINT OF VIEW
Polarization
Time Quadrature
Physical dimensions
FrequencySpace
t
f
O E S C L
1300
0
1400 1500 1600
0.3
0.6
0.9
1.2
Wavelength [nm]
Loss[dB]
13601260 1460 1530
1565
1625
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3.1Intensity modulation
MODULATING THE INTENSITY DIMENSION
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MODULATING THE INTENSITY DIMENSION
Easiest property to modulate
Use absorptionor interferenceprocesses
Intensity
p
in
datap
[P.J. Winzer et al., Proc. IEEE, p.952 (2006).]
DETECTING THE INTENSITY DIMENSION
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DETECTING THE INTENSITY DIMENSION
Practical detection schemes are important for high-speed optical systems.
Practical modulation techniques are important for high-speed optical systems.
Photodetection
Electrical signalOptical intensity
1)Demodulation refers to the process of moving an (optical) passband signal to (electrical) baseband, while
detection refers to the extraction of digital information out of the baseband signal.
Easiest property to modulate
Use absorptionor interference
Easiest property to demodulate
'Direct detection' (better1): 'demodulation) = optical intensity detection,photodetection
Intensity
THE #1 TRANSPONDER DESIGN STRATEGY
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THE #1 TRANSPONDER DESIGN STRATEGYMODULATE AS FAST AS ECONOMICALLY FEASIBLE
Space
PolarizationFrequency
Time Quadrature
Physical dimensions
10 Gb/s25 Gb/s
53.5 Gb/s 107 Gb/s
Research:
107-Gb/s electrical signal
[Winzer et al., ECOC05]100G Photo-receiver
[Sinsky et al., OFC07]
100G CDR Demux
[Derksen et al., OFC06]
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3.2Phase modulation
OPTO ELECTRONIC CONVERTERS DETECT INTENSITIES
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OPTO-ELECTRONIC CONVERTERS DETECT INTENSITIES
Photodetection
Electrical signalOptical intensity
Intensity PhasePhase-to-amplitude conversion at detection
Also known as interference in optics
Local oscillator laser (coherent receiver)
Signal self-reference (differential mod.)
Direct detection with delay demodulation
Differential phase modulation
Information in phase difference
Coherent receiver
BINARY DIFFERENTIAL PHASE MODULATION
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constructive
destructive
balanced
Detector amplitude imbalanceOSNR
penalty
[dB]
BINARY DIFFERENTIAL PHASE MODULATIONNEED BALANCED DETECTION TO GAIN 3 dB
[Gnauck et al., JLT, 115 (2005)]
Im{E}
Re{E}
OOK DPSK
Im{E}
Re{E}
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3.3Multi-level modulation
NEED HIGHER BIT RATES ?
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NEED HIGHER BIT RATES ?ONE OPTION: MULTI-LEVEL
Space
PolarizationFrequency
Time Quadrature
Physical dimensions
10 Gb/s
25 Gb/s
53.5 Gb/s 107 Gb/s
50 Gb/s
Multilevel (PAM)
PAM: Pulse amplitude modulation
10
11
01
00
NEED HIGHER BIT RATES ?
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NEED HIGHER BIT RATES ?ONE OPTION: MULTI-LEVEL
Space
PolarizationFrequency
Time Quadrature
Physical dimensions
10 Gb/s
25 Gb/s 50 Gb/s
Multilevel (PAM)
PAM: Pulse amplitude modulation
[Gnauck et al., OFC 2011]
56 Gb/s (28 GBd) 112 Gb/s (56 GBd) 160 Gb/s (80 GBd)
[Winzer et al., ECOC 2011] [Raybon et al., PTL 2012] [Raybon et al., ECOC 2013]
214 Gb/s (107 GBd)
QUADRATURE PHASE SHIFT KEYING (QPSK)
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QUADRATURE PHASE SHIFT KEYING (QPSK)MULTI-LEVEL IN BOTH QUADRATURES
Im{E}
Re{E}
16-QAM TRANSMITTER
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16-QAM TRANSMITTERUSING A DAC AND AN I/Q MODULATOR
6 dB6 dB
2-bit arbitrary waveform generator
Multiple-bitdelay
Im{E}
Re{E}4
4
IntegratedI/Q Modulator
p/2
PRBS: Pseudo-random bit sequence
I/Q: In-phase/quadrature (or: Re{E} / Im{E})
215
-1PRBS at14.0 Gb/s
D1
D1
D2
D2
6 dB
6 dB
(D2outputshalf-patterndelayed wrtD1 outputs)
11-GHz LPF
11-GHz LPF
Laser
[Winzer et al., ECOC08]
HIGHER-LEVEL FORMATS
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p/2
N-level Electronic Signal I
N-level Electronic Signal Q
Laser N2QAM Signal
Format N Bits/symbol
QPSK 2 216-QAM 4 4
64-QAM 8 6
256-QAM 16 8
N2-QAM N 2 log2(N)
8-level drive for 64-QAM
HIGHER-LEVEL FORMATSUSING A DAC AND AN I/Q MODULATOR
[A. Sano et al., ECOC2010, PD2.4]
[J. Godin et al., BLTJ, 2013] 21.4 GBaud
10 GBaud
[J. Godin et al., BLTJ, 2013]
50 GBaud
CONSTELLATION SIZE VERSUS SYMBOL RATE
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CONSTELLATION SIZE VERSUS SYMBOL RATE
1 2 3 4 5 6 7 8 9
100
200
300
Bits per symbol
Linera
te[Gb/s]
16-QAM
[Winzer, J. Lightwave Technol. 30, 3824 (2012)]
PDM 512-QAM
3 GBaud (27 Gb/s)[Okamoto et al., ECOC10]
PDM 256-QAM
4 GBaud (32 Gb/s)[Nakazawa et al., OFC10]
PDM 64-QAM
21 GBaud (128 Gb/s)[Gnauck et al., OFC11]
PDM 16-QAM
80 GBaud (320 Gb/s)[Raybon et al., PTL12]
PDM QPSK
107 GBaud (224 Gb/s)[Raybon et al., PTL12]
ADC & DAC resolution Bandwidth
[R. H. Walden, JSAC (1999), and Proc. CSIC (2008)][A. Khilo et al., Opt. Ex. (2012)]
SCALING THROUGH MORE LEVELS OR SYMBOL RATE ?
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SCALING THROUGH MORE LEVELS OR SYMBOL RATE ?
PDM 512-QAM
3 GBaud (54 Gb/s)[Okamoto et al., ECOC10]
PDM 256-QAM
4 GBaud (64 Gb/s)[Nakazawa et al., OFC10]
PDM 64-QAM
21 GBaud (256 Gb/s)[Gnauck et al., OFC11]
PDM 16-QAM
80 GBaud (640 Gb/s)[Raybon et al., IPC12]
Logarithmic scaling Linear scaling
PDM QPSK
107 GBaud (448 Gb/s)[Raybon et al., ECOC12]
[T. Pfau et al., J. Lightwave Technol. 27(8), 989 (2009)]
[Winzer, J. Lightwave Technol. 30, 3824 (2012)]
PRACTICAL CONSIDERATIONS
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PRACTICAL CONSIDERATIONSIMPLEMENTATION PENALTY
98
7
6
54
3
2
1Bitspersymbol(perpolarization)
2.0
1.5
1.5
0.70.9
0.5
0.6
3.3
1.6
1.0
2.1
0.72.4
1.3
0.9
0.6
2 2
2.4
1.7
2.8
0.6
0.5
4.3
10 100
Symbol rate [Gbaud]
5 20 50
[Winzer, J. Lightwave Technol. 30, 3824 (2012)]
EVOLUTION OF HIGH-SPEED TRANSPONDERS
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EVOLUTION OF HIGH SPEED TRANSPONDERSTOWARDS 1 TB/S ON A SINGLE CARRIER
Space
Polarization
Frequency
Time Quadrature
Physical dimensions
1986 1990 1994 1998 2002 2006
10
100
2010 2014 2018
1
2022
107 Gbaud QPSK
1000
Serialinterfacerates[Gb/s]
107 Gbaud 16-QAM (856 Gb/s)
72 GBd PDM-64-QAM (864 Gb/s)
[Randel et al, 2014]
[Raybon et al, 2013]
SPECTRAL EFFICIENCY AND ITS PRICE IN SNR
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SPECTRAL EFFICIENCY AND ITS PRICE IN SNR
20 years ago:Device physics set engineeringlimitson spectral efficiency
Today:Information theory sets fundamentallimitson spectral efficiency
Simple on-off modulation,direct detection
Higher-order modulation,coherent detection
0.01
0.1
1
10
Spectralefficiency
perpolarizatio
n[b/s/Hz]
1990 1994 1998 2002 2006Year
2010
Laser & filter stability
x-pol
y-pol
x-pol
y-pol
Modulation
PDM
~1 dB/year
Detection
0 5 10 15 20 25
1
10
Required SNR per bit [dB]
Spectralefficiency
perpolarization[b/s/Hz]
3.7 dB 8.8 dB
2x
2x16
64
4
256SE = log
2(1 + SNR)
LOW SPECTRAL EFFICIENCY MODULATION
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LOW SPECTRAL EFFICIENCY MODULATION(SPACEBORNE APPLICATIONS)
0 5 10 15 20 25
0.1
1
10
SNR (photons)per bit [dB]
Sp
ectralefficiency[b/s/Hz]
Sensitivity-constrained
Capacity-constrained
Intensity
Pulse Position Modulation (PPM)
1 0 0 1 1 1
Position within PPM symbolTime
0 0
4
8
16
32
64
PPM
256
LOW SPECTRAL EFFICIENCY MODULATION
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LOW SPECTRAL EFFICIENCY MODULATION(SPACEBORNE APPLICATIONS)
0 5 10 15 20 25
0.1
1
10
SNR (photons)per bit [dB]
Sp
ectralefficiency[b/s/Hz]
Sensitivity-constrained
Capacity-constrained
4
8
16
32
64
PPM
256
Shot-noise limited
channels
Intensity
Pulse Position Modulation (PPM)
1 0 0 1 1 1
Position within PPM symbolTime
0 0
FROM CLASSICAL TO QUANTUM TECHNIQUES
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FROM CLASSICAL TO QUANTUM TECHNIQUES[J. Gordon, Quantum effects in communication systems, Proc. IRE 50, 1898 (1962)]
[A. S. Holevo, The capacity of a quantum channel with general signal states, Trans. Inf. Theory 44, 269 (1998)]
0.001 0.01 0.1 1 10 100Spectral efficiency [bits/s/Hz]
-20
-10
0
10
Sensitivity[dBbits/photon]
Linear Shannon
Photon counting
Gordon/Holevoquantum capacity
???
Classical Quantum
[C. Antonelli et al., J. Lightwave Technol. (2014)]
SOME MORE ADVANCED TRICKS
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[Karlsson & Agrell, ECOC10]
[Cai et al., ECOC10]
ISI
MAP
SOME MORE ADVANCED TRICKS4D, CODING, SHAPING, OVER-FILTERING
Whatever you do, Shannon will be the limit[C. E. Shannon, BLTJ (1948)]
0 5 10 15 20 25
1
10
Required SNR per bit [dB]
16-QAM
64-QAM
4-QAM
256-QAMConstellationshaping
Over-filtering
Coded modulation[Liu et al., OFC12]
Spectralefficiency[b/s/H
z]
ISI: Inter-symbol interference; MAP: Maximum a posteriori
4-DIMENSIONAL MODULATION
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4 DIMENSIONAL MODULATIONCLOSER SYMBOL PACKING THROUGH CORRELATIONS
Re{E}
4
Simple 2D example:16-QAM, viewed as 2 independent, orthogonally muxed 4-PAMs
Im{E}
Re{E}4
4
Im{E}
Re{E}4
Im{E}
+ =
Re{E}4
4
Im{E}
Here, the two dimensionsare no longer independent2D modulationSacrifice SE for performance [Karlsson & Agrell, ECOC10]
In 4D space:(Ix/Qx/Iy/Qy)
[H. Buelow et al., OFC 2013]
+ =
DIGITAL PULSE SHAPING
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DIGITAL PULSE SHAPINGPULSE BANDWIDTH AND SPECTRAL EFFICIENCY
10 dB
56 GHzSpectrum[dB]
Frequency
Spectral efficiency =Information bits
Signal spectral width
MODERN OPTICAL TRANSPONDERS
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MODERN OPTICAL TRANSPONDERSDIGITAL PULSE SHAPING
DAC
DAC
DAC
DAC
TransmitDSP
PDMI/Q-MOD
TX Laser
t
f
First 200G 16-QAM coherent interfaceAlcatel-Lucent 2013
Modern coherent transponders use pulse shaping for: Spectral efficiency Pre-compensation of various fiber impairments
(dispersion, nonlinearity, filtering)
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4Coherent detection and
digital signal processing
COHERENT DETECTION BASICS
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Local
Oscillator (LO)
Signal|ESig(t) + ELO|
2 = |ESig(t)|2+ |ELO|
22 Re{ESig(t) ELO e }
Beat term
90-deg shifted LO
Signal
Second signal quadrature Im{ESig(t) ELO e }
90-deg hybrid
Requires signal-LOpolarization alignment
j2pfIFt+jfSig(t)
j2pfIFt+jfSig(t)
COHERENT DETECTION BASICS
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Local
Oscillator (LO)
Signal
90-deg shifted LO
Signal
Local
Oscillator (LO)
Signal
90-deg shifted LO
Signal
x-polarization y-polarization
The good news:Polarization multiplexing
comes for free
Polarization-diversity 90-degree hybrid
COHERENT DETECTION BASICS
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THE ROLE OF THE INTERMEDIATE FREQUENCY
Heterodyne Homodyne Intradyne
Front-end bandwidth ~ 5* Symbol rate Symbol rate ~Symbol rate
Phase/frequency locking Frequency locking Analog optical PLLDigital electronic PLL
(free-running LO)
Spectral sketch
Constellation sketch
fIF0 f0 IF
LocalOscillator (LO)
f
Signal|ESig(t) + ELO|2: 2 Re{ESig(t) ELO e }
Beat term
Im{E}
Re{E}
Im{E}
Re{E}
Im{E}
Re{E}
j2pfIFt +jfSig(t)
MODERN COHERENT DETECTION
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DO AS MUCH AS YOU CAN DIGITALLY, IN CMOS
LO Local oscillator
DSP Digital signal processing
Coherent optical front-end
Im{E}
Re{E}
90 degHybrid
90 degHybrid
PBS
LO laserPBS
Signal
In-phase component
Quadrature component
In-phase component
Quadrature component
x-pol.
y-pol.
f0
PBS Polarization beam splitter
A/D Analog-to-digital conversion
x pol.
y pol.
MODERN COHERENT DETECTION
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A/D
A/D
A/D
A/D
Ix
Qx
Iy
Qy
Digitization
HIGH-SPEED A/D CONVERSIONIN THE LAB
Agilent90000 Q-Series
160 GS/s @ 63GHz
LeCroyLabMaster 10Zi
160 GS/s @ 65 GHzLO Local oscillatorDSP Digital signal processing
90 degHybrid
90 degHybrid
PBS
LO laserPBS
Signal
PBS Polarization beam splitter
A/D Analog-to-digital conversion
Coherent optical front-end
x pol.
y pol.
MODERN COHERENT DETECTION
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A/D
A/D
A/D
A/D
Ix
Qx
Iy
Qy
Digitization
HIGH-SPEED A/D CONVERSIONON CHIP
LO Local oscillator
DSP Digital signal processing
90 degHybrid
90 degHybrid
PBS
LO laserPBS
Signal
PBS Polarization beam splitter
A/D Analog-to-digital conversion
Coherent optical front-end
x pol.
y pol.
MAIN COHERENT DSP BUILDING BLOCKS
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Chromaticdispersion
Front-endcorrec
tions
A/D
A/D
A/D
A/D
+j
+j
Ix
Qx
Iy
Qy
Digital computation ofexp(-j a f2 )
Transmit pulse Dispersed received pulse Compensated pulse
Fiber DSP
MAIN COHERENT DSP BUILDING BLOCKS
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Chromaticdispersion
Front-endcorrec
tions
A/D
A/D
A/D
A/D
+j
+j
Ix
Qx
Iy
Qy
Digital computation ofexp(-j a f2 )
Transmit pulse
Fiber
with LO phase noise
Dispersed received pulse
Received phase
Ideal
Compensated pulse
Local oscillator laser needs to be coherentacross dispersed pulse width
Electronically enhanced laser phase noise
[W. Shieh et al., Opt. Exp., vol. 16, 15718 (2008)][C. Xie, Proc. OFC, OMT4 (2009)]
MAIN COHERENT DSP BUILDING BLOCKS
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Chromaticdispe
rsion
Clockrecovery
Retiming,resam
pling
Front-endcorrec
tions
A/D
A/D
A/D
A/D
+j
+j
Ix
Qx
Iy
Qy
PBS
x
y Polarization rotationSignal 1
Signal 2
Axx
x + Axy
y
Ayxx + Ayyy
PBSFiber
Jones matrix inversion
MAIN COHERENT DSP BUILDING BLOCKS
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Chromaticdispe
rsion
Clockrecovery
Retiming,resam
pling Hxx
Hyy
+
Hxy
+
Hyx
Front-endcorrec
tions
A/D
A/D
A/D
A/D
+j
+j
Ix
Qx
Iy
Qy
PBS
x
y Polarization rotationSignal 1
Signal 2
Axx
x + Axy
y
Ayxx + Ayyy
PBSFiber
MAIN COHERENT DSP BUILDING BLOCKS
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Chromaticdispe
rsion
Clockrecovery
Retiming,resam
pling Hxx
Hyy
+
Hxy
+
Hyx
Front-endcorrec
tions
A/D
A/D
A/D
A/D
+j
+j
Ix
Qx
Iy
QyFrequencylock
ing
Phasetrackin
g
Im{E}
Re{E}f0
MAIN COHERENT DSP BUILDING BLOCKS
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[T. Mizuochi et al., Proc. OFC, 2012 ]
Chromaticdispe
rsion
Clockrecovery
Retiming,resam
pling Hxx
Hyy
+
Hxy
+
Hyx
Front-endcorrec
tions
A/D
A/D
A/D
A/D
+j
+j
Ix
Qx
Iy
QyFrequencylock
ing
Phasetrackin
g
D
ecision/Decod
ing
A WORD ON FEC IN OPTICAL SYSTEMS
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FEC
decoder
BER = 210-3 BER = 10-16
-Log(Uncorrected BER)
-Log(CorrectedBER)
Hard decision, 7% Overhead
FEC correction threshold
Thats how most optical communications engineers view FEC:
Assumes hard-decision FEC Assumes independent errors
(sufficient scrambling wrt burst errors)
Problem:Soft-decision FEC
A WORD ON SOFT FEC IN OPTICAL SYSTEMS
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Thats what nonlinearities can do:(Outside the assumptions leading to the Gaussian Noise model)
[J. Cho et al., Optics Express, 7915 (2012)]
A WORD ON SOFT FEC IN OPTICAL SYSTEMS
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Thats what nonlinearities can do:(Outside the assumptions leading to the Gaussian Noise model)
[A. Leven et al., Phot. Technol. Lett., 1547 (2011)]
A WORD ON SOFT FEC IN OPTICAL SYSTEMS
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Back-to-back After 1600-km transmission
Gaussian-like signal statistics down to ~1E-5 even after 1600-km transmission
The performance of SD-FEC expected to be fully obtained.
MAJOR DSP ASIC MILESTONES IN OPTICS
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2005 2006 2007 2008 2009 2010 201110
0
101
102
Year
GateCounts(Million) ~70% per year
2
3
4
5
6
7
8
9
0 10 20 30 40 50 60
Sample rate [GS/s]
Numberofbit
Stated
ENOB
Nortel electronic pre-EDC 10G Tx (2005)
20GS/s DAC
ADC resolution vs. sample rate
Nortel 40Gb/s PDM-QPSK (2007)
20GS/s ADC/DSP
Alcatel-Lucent 112Gb/s (2010)
56GS/s ADC/DSP
70M+ gates
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5Multiplexing in optical
communication systems
SAME 5 DIMENSIONS FOR MULTIPLEXING
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AN EXHAUSTIVE LIST
Polarization
Time Quadrature
Physical dimensions
FrequencySpace
t
f
O E S C L
13000
1400 1500 1600
0.3
0.6
0.9
1.2
Wavelength [nm]
Loss[dB]
13601260 1460 1530
1565
1625
WAVELENGTH-DIVISION MULTIPLEXING (WDM)
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Orthogonality through non-overlapping frequency bins (WDM)
VARIOUS SUPERCHANNEL DEMONSTRATIONS
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1 Tb/s(2 subcarriers) 16-QAM
5.2 bit/s/Hz
3200 km transmission[Raybon et al., IPC12]
263 GHz
1.5 Tb/s(8 subcarriers) 16-QAM
5.7 bit/s/Hz
5600 km transmission[Liu et al., ECOC12]
1.2 Tb/s(24 subcarriers) QPSK
3.74 bit/s/Hz
7200 km transmission[Chandrasekhar et al., ECOC09]
300 GHz
ADC&DAC bandwid th & resolut ion Opt ical paral lel ism
200 GHz
1 Tb/s(4 subcarriers) 16-QAM
5.0 bit/s/Hz
2400 km transmission[Renaudier et al., OFC12]
200 GHz
Few carriers
High symbol rate
Large # of carriers
Lower symbol rateMod.
f
Mod.
Mod.
Mod.
Laser
f
+
Laser
Laser
Laser
f
f
f
OFDM IN OPTICAL COMMUNICATIONS
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Optical OFDM
f
All subcarriers modulated individually
Parallel optical hardware
f
Electrical OFDM
56 Gb/s net rate (65 Gb/s line rate)
32-QAM per subcarrier[Takahashi et al., OFC09]
All subcarriers modulated at oncef
f
Mod.Laser
Mod.
Comb
ff
f
f
f
Mod.
Mod.
Mod.
60 GHz
448 Gb/s (10 subcarrier) 16-QAM5 bit/s/Hz2000 km transm.[X. Liu et al., OFC10]
65 GHz
606 Gb/s (10 subcarrier) 32-QAM7 bit/s/Hz2000 km transm.[X. Liu et al., ECOC10]
1.2 Tb/s (24 subcarrier) QPSK3 bit/s/Hz7200 km transm.[S. Chandrasekhar et al., ECOC09]
300 GHz
POLARIZATION-DIVISION MULTIPLEXING (PDM)
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A standard single-mode fiber supports two orthogonal polarizations
One can transport independent signals in both polarizations, provided
that one can separate them again at the receiver in the presence of
random polarization rotations within the transmission fiber
Polarization diversity receivers detect both polarizations
(see section on coherent detection below)
PDM increases spectral efficiency by a factor of 2
SPACE-DIVISION MULTIPLEXING (SDM)
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Spatially disjoint optical beams are orthogonal
Multiple fiber strands
Multi-core fiber
http://www.occfiber.com/
Spatially overlapping optical beams can also be orthogonal
Multiple modes in multi-mode fiber
provided that one can selectively excite and detect those modes
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6Capacity limits
THE NONLINEAR SHANNON LIMIT
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Increasing the signal power (i.e. the SNR) creates signal distortions from fiber
nonlinearity, eventually limiting system performance
SNR [dB]
CapacityC
[bits/s] Maximum
capacity
Signal launch power [dBm]
Tx Rx
Distributed Noise
C = B log2(1 + SNR)
Nonlinear distortions
Quantum mechanics dictates a lower bound on amplifier noise
[R.-J. Essiambre et al., Phys. Rev. Lett. (2008) or J. Lightwave Technol. (2010)]
AN LOWER BOUND ESTIMATE FOR THE SHANNON LIMIT Assume ring constellations
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Assume ring constellations
Deterministic signal back-propagation to remove (most of the) channel memory
Numerical solution of nonlinear Schrdinger equation Numerical statistics
SNR [dB]
CapacityC
[bits/s] Maximum
capacity
Signal launch power [dBm]
Tx Rx
Distributed Noise
[R.-J. Essiambre et al., Phys. Rev. Lett. (2008) or J. Lightwave Technol. (2010)]
0 5 10 15 20 25 30 35 40
SNR (dB)
Capacityperunitbandwidt
h
(bits/s
/Hz)
0
1
2
3
4
5
6
8
71 ring2 rings4 rings8 rings
16 rings
Numerical statistics
SOME EXAMPLE RESULTS
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0 5 10 15 20 25 30 35 40
SNR (dB)
Capacityperun
itbandwidth
(bits/s/Hz)
0
1
2
3
4
5
6
8
7
1 ring2 rings4 rings8 rings16 rings-0.2 -0.1 0 0.1 0.2
-0.2
-0.1
0
0.1
0.2
Imagpartoffield
[mW1/
2]
Real part of field [ mW1/2
]
-1 -0.5 0 0.5 1
-1
-0.5
0
0.5
1
Real part of field [ mW1/2
]
Imagpartoffield[mW1/
2]
-2 -1 0 1 2
-2
-1
0
1
2
Real part of field [ mW1/2
]
Imagpartoffield[m
W1/
2]
R.-J. Essiambre et al., Phys. Rev. Lett. (2008) or J. Lightwave Technol. (2010)
Note:Capacity maximum occurs at fairly high SNRs
VARIOUS CONTRIBUTIONS TO CAPACITY
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R.-J. Essiambre et al., J. Lightwave Technol. (2010)
SENSITIVITY ANALYSIS TO FIBER PARAMETERS
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Capacity is fairly insensitive to (heroic!)
improvements of fiber loss, nonlinearity,
or dispersion
Dont waste your money improving
single-mode fiber...
[R.J.Essiambre and R.W.Tkach, Proc. IEEE, 2012]
THE RATE-REACH TRADE-OFF IN OPTICAL FIBER
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101
5
10
15
2100 1,000 10,000
Transmission distance [km]
Spectralefficiency[b/s/Hz]
Metro Long-haul Submarine
25
50
75
10
C-bandcapa
city[Tb/s]
THE RATE-REACH TRADE-OFF IN OPTICAL FIBER
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5
10
15
2100 1,000 10,000
Transmission distance [km]
Spectralefficiency[b/s/Hz]
Metro Long-haul Submarine
25
50
75
10
C-bandcapa
city[Tb/s]