Next-Generation High-Capacity Submarine Transmission

1
ALCATEL-LUCENT — PROPRIETARY AND CONFIDENTIAL — RESTRICTED — SOLELY FOR AUTHORIZED PERSONS HAVING A NEED TO KNOW.
COPYRIGHT © 2015 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Next Generation High Capacity Submarine Transmission
Rafael R. Müller
J. Renaudier, L. Schmalen, A. Ghazisaedi, G. Charlet
28/Jun – WTON 2015 – Campinas - Brazil

2
Agenda
1. Overview of submarine networks
2. Capacity-approaching error correction
3. Transponder flexibility
4. Non-linear mitigation
5. Beyond 400 Gb/s per channel
6. Conclusion

3

4
10000 km
10 Terabit/s
100 M£
20 years

5
Cables, amplifiers and branching units
Branching
unit (1x2)
750kg
Up to 1.4m long~10 fibers
copper (power
feeding)
diameter ~2cm
No dynamic gain equalizer (no WSS) for
reliability
Single stage EDFA gain tailored to span loss
Premium fiber (>10x more expensive) w/
larger effective area, larger dispersion and
lower attenuation.
Coherent
receiver + DSP
DEMUX
MUX
Transmitter

6
Evolution of spectral efficiency
Lab ideas quickly introduced in commercial products
-20
-15
-10
-5
0
5
10
1995 2000 2005 2010 2015
Spectralefficiency
(logscale,5dB/div)
5Gb/s
10Gb/s
40Gb/s
100Gb/s
200Gb/s
250Gb/s
Commercial systems
1
3.3
10
0.33
0.1
0.03 2.5Gb/s 100GHz
10Gb/s 33GHz
40Gb/s 50GHz
100Gb/s 40GHz
20152010200520001995
Lab experiments
[1] R. Rios-Müller, et al. "Optimized spectrally efficient transceiver for 400-Gb/s single carrier
transport.“ ECOC’ 14, PD.4.2
400 Gb/s 66.7 GHz over
transatlantic distance [1]

7
Perfomance vs. transponder complexity
Diminishing performance gains as we approach fiber capacity limit
2000 2015
time
Performance
Complexity
Intensity-modulated laser Transmitter Low-linewidth laser + I/Q
modulator + polarization diversity
+ DAC
1 photodiode Receiver Low-linewidth laser + 90° hybrid +
4 balanced photodiodes + ADC
+DSP
Single-Pol OOK Modulation Dual-Pol QAM
7% hard-decision FEC Channel coding 20% soft-decision FEC

8
Evolution of fiber capacity
50 Terabit/s in lab
Combination of techniques
1
2
4
8
16
32
64
2000 2002 2004 2006 2008 2010 2012 2014
Capacity(Tb/s)perfiber
Year
50Tb/s
10Gb/s
Coherent detection























1
01
01
01
0
H
HH
HH
HH
H
Hconv
-75
-65
-55
-45
-35
1528 1538 1548 1558 1568 1578 1588 1598
Power[10dB/div]
Wavelength [nm]
16QAM
Spatially
coupled soft
decision FEC
Ultra wide
amplification
-70
-65
-60
-55
-50
-45
-40
-35
-30
1546,2 1546,3 1546,4 1546,5 1546,6 1546,7 1546,8 1546,9 1547
Wavelength (0.1nm/div)
Power(5dB/div)
“NRZ”
RRC
0.01
Nyquist pulse
shaping
40Gb/s
(per wavelength)
200Gb/s +
100Gb/s
[2] A. Ghazisaeidi, et al. "52.9 Tb/s transmission over transoceanic distances using adaptive multi-
rate FEC.“ ECOC’14 , PD.3.4
52.9 Tb/s [2]
C L

9
How to boost performance?
Methods
Nonlinear
mitigation
Transponder
flexibility
Capacity
approaching
error
correction

10
Agenda
6. Conclusion

11
Error correction coding basics
Methods
NL
FLEXFEC
1E-16
1E-14
1E-12
1E-10
1E-08
1E-06
0.0001
0.01
1
0 5 10 15 20
Biterrorratio
Signal-to-noise ratio [dB]
Coding gain
@10-15
Uncoded
rate= k/n
overhead=n/k-1
Net coding gain=coding gain-rate loss
=coding gain+10log10(rate)
Uncoded bits
Parity check bits

12
Error correction coding basics
MAP decoding: optimal solution but computationally intractable
BP decoding: sub-optimal but practical for large blocks
Methods
NL
FLEXFEC
1E-16
1E-14
1E-12
1E-10
1E-08
1E-06
0.0001
0.01
1
0 5 10 15 20
Biterrorratio
Coding gain
@10-15
Belief-propagation
decoding
MAP decoding
Uncoded
rate= k/n
overhead=n/k-1
Net coding gain=coding gain-rate loss
=coding gain+10log10(rate)
Uncoded bits
Parity check bits

13
Net coding gain vs overhead
Hard-decision to soft-decision
Low-overhead to high-overhead
5
6
7
8
9
10
11
12
13
14
0 10 20 30
Netcodinggain[dB]
FEC overhead [%]
Methods
NL
FLEXFEC
1st gen:
7% HD-FEC
Product-codes
2ndgen:
20% SD-FEC
LDPC

14
How to approach MAP decoding in polynomial time?
Terminated spatially-coupled codes behave like uncoupled codes under MAP decoding
However, block-length should be large to minimize rate loss due to termination
Methods
NL
FLEXFEC
1E-16
1E-14
1E-12
1E-10
1E-08
1E-06
0.0001
0.01
1
0 5 10 15 20
Biterrorratio
Coding gain
@10-15
Belief-propagation
decoding
MAP decoding
Uncoded
Underlying block code
Uncoded bits
Parity check bits
Coupling
• Efficient window decoder
•Trade-off complexity performance

15
State-of-the-art spatially coupled LDPC
Excellent performance with FPGA verification up to 10-15 BER
Methods
NL
FLEXFEC
[3] L. Schmalen, et al. "Evaluation of left-terminated spatially coupled LDPC codes for optical
communications." ECOC’14 , Th.2.3.4
[3]

16
State-of-the-art spatially coupled LDPC
Excellent performance with FPGA verification up to 10-15 BER
Methods
NL
FLEXFEC
[3] L. Schmalen, et al. "Evaluation of left-terminated spatially coupled LDPC codes for optical
communications." ECOC’14 , Th.2.3.4
5
6
7
8
9
10
11
12
13
14
0 10 20 30
Netcodinggain[dB]
FEC overhead [%]
7% HD-FEC
20% SD-FEC
25% Spatially-
coupled LDPC[3]
[3]

17
Increasing overhead is always good?
Electronics bandwidth limit FEC overhead
15.4 19.4 23.4 27.4 31.3
15
16
17
18
19
20
21
22
58 60 62 64 66
FEC Overhead [%]
RequiredOSNR[dB/0.1nm]
Symbol rate [Gbaud]
400 Gb/s [1]
Experimental required OSNR
-50
-40
-30
-20
-10
-40 -20 0 20 40Frequency [20GHz/div]
After
Waveshaper
-50
-40
-30
-20
-10
-40 -20 0 20 40Frequency [20 GHz/div]
Before
Waveshaper
32 GHz
15 dB
3dB
I/Q mod
DAC
0, 33, 67 and 100%
pre-emphasis
-16
-12
-8
-4
0
-40 -20 0 20 40Power… Frequency [20GHz/div]
Power[10dB/div]
Power[10dB/div]
Power
[4dB/div]
33%
67%
100%
Driver
WaveshaperEDFA
Methods
NL
FLEXFEC
[1] R. Rios-Müller, et al. "Optimized spectrally efficient transceiver for 400-Gb/s single carrier transport.“ ECOC’ 14, PD.4.2

18
Agenda
6. Conclusion

19
Flexibility, why?
2000
3 4 5 6 7 8 9
Reach(km)@4.10-3BER
Bits per 4D symbol
PDM-QPSK
(3 b/s/Hz)
PDM-8QAM
(4.5 b/s/Hz)
PDM-16QAM
(6 b/s/Hz)
4000
8000
12000
16000
20000
2000
Methods
NL
FLEXFEC
[4] J. Renaudier. et al ”Experimental transmission of Nyquist pulse shaped 4-D coded modulation using dual polarization 16QAM
set-partitioning schemes at 28 Gbaud” OFC’13 (OTu3B-1)
[4]

20
Flexibility, why?
New formats fill the gap between existing solutions
Maximize capacity for a given reach
2000
3 4 5 6 7 8 9
Reach(km)@4.10-3BER
Bits per 4D symbol
PDM-QPSK
(3 b/s/Hz)
32SP-16QAM
(3.75 b/s/Hz)
PDM-8QAM
(4.5 b/s/Hz)
128SP-16QAM
(5.25 b/s/Hz)
PDM-16QAM
(6 b/s/Hz)
4000
8000
12000
16000
20000
2000
Methods
NL
FLEXFEC
[4] J. Renaudier. et al ”Experimental transmission of Nyquist pulse shaped 4-D coded modulation using dual polarization 16QAM
set-partitioning schemes at 28 Gbaud” OFC’13 (OTu3B-1)
[4]

21
Extreme case of flexibility
3
4
5
6
1530 1540 1550 1560
Q2-factor[dB]
Wavelength[nm]
Methods
NL
FLEXFEC
[2] A. Ghazisaeidi, et al.
"52.9 Tb/s transmission
over transoceanic
distances using adaptive
multi-rate FEC.“ ECOC’14
PD.3.4
Perfomance of
~160 ch in C-band
• Single FEC limit
• Single capacity per channel
• Total capacity limited by worst channel

22
3
4
5
6
1530 1540 1550 1560
Q2-factor[dB]
Wavelength[nm]
Methods
NL
FLEXFEC
over transoceanic
PD.3.4
Perfomance of
~160 ch in C-band
• Dual FEC limit
• Two possible bitrates per channel
• Peformance gain compared to homogeneous bitrate

23
Flexibility recovers performance lost due to undesirable variability
3
4
5
6
1530 1540 1550 1560
Q2-factor[dB]
Wavelength[nm]
25
30
35
40
45
50
55
1 2 3 4 5 6 7 8 9 10 11 12
Capacityperfiber
[Tb/sC+Lband]
Number of bitrates
Methods
NL
FLEXFEC
over transoceanic
PD.3.4
After 6600 km
After 10200 km
10 Tb/s
8 Tb/s
Perfomance of
~160 ch in C-band

24
Agenda
6. Conclusion

25
How to mitigate nonlinear effects?
Optical channel: long memory (>1000 symbols in submarine systems)
Linear (dispersion) and nonlinear impairments are distributed
Methods
NL
FLEXFEC
L km
Nonlinear fiber
NL NL NL
Lumped nonlinear
element
L/N km
Linear fiber
Split-step
propagation
aproximation

26
How to mitigate nonlinear effects?
Optical channel: long memory (>1000 symbols in submarine systems)
Linear (dispersion) and nonlinear impairments are distributed
XFFT FFT-1
i⅟2β2ω2h |·|2 FFT X
H(f)
FFT-1 X
(⁸⁄₉)κγheffP
e(i·)
X
input output
x M
Methods
NL
FLEXFEC
L km
Nonlinear fiber
NL NL NL
Lumped nonlinear
element
L/N km
Linear fiber
Split-step
propagation
aproximation
1 step of filtered digital backpropagation

27
Perturbative nonlinear mitigation
• Channel model using perturbative theory
Pre-calculate deterministic distortion and subtract it
Efficiently calculated using a running double-sum at symbol rate
Similar performance compared to digital backpropagation
 
  
 
 

 



N
Nm
N
Nn
V
tnmnmt
H
nt
V
mt
H
nmt
V
nt
V
mt
VH
t
H
t
N
Nm
N
Nn
H
tnmnmt
V
nt
H
mt
V
nmt
H
nt
H
mt
HH
t
H
t
nCxxxxxxxy
nCxxxxxxxy
,
**
,
**
Methods
NL
FLEXFEC
Depends on type of fiber, power per channel, span (total) length, baudrate, etc

28
Experimental results
400 Gb/s single-carrier
400 Gb/s transatlantic distance transmission possible thanks to NL mitigation
1 step every 4 spans, (30 steps for 6600 km)
3
4
5
6
13 14 15 16 17
Q2-factor[dB]
Power [dBm]
3
4
5
6
1548.5 1549.5 1550.5 1551.5
Q2-factor[dB]
Lambda [nm]
6600 km
FEC limit
Methods
NL
FLEXFEC
6000 km
[1] R. Rios-Müller, et al. "Optimized spectrally efficient transceiver for 400-Gb/s single carrier
transport.“ ECOC’ 14, PD.4.2
14 15 16 17
Power [dBm]
WITH Filtered digital backpropagation
WITHOUT Filtered digital backpropagation

29
Experimental results
52 Tb/s experiment
NL mitigation provides ~3 Tb/s capacity gain
Methods
NL
FLEXFEC
25
30
35
40
45
50
55
1 2 3 4 5 6 7 8 9 10 11 12
Capacityperfiber[Tb/sC+L
band]
Number of bitrate
[2] A. Ghazisaeidi, et al. "52.9 Tb/s transmission over transoceanic distances using adaptive multi-rate
FEC.“ ECOC’14 PD.3.4
After 6600 km
After 10200 km
3 Tb/s
3 Tb/s

30
Putting all together
Combine 3 methods
Choose combination that minimizes the cost (development, power, etc)
Methods
NL
FLEXFEC
NLFLEXFEC + +

31
Agenda
6. Conclusion

32
Beyond 400 Gb/s
ECL MZM
32.5 GHz
1545.72nm
EDFA
10 MHz
Delay Line
DL
DL
I/Q-mod2
TX DSP
I/Q-mod3
I/Q-mod4
DAC
I/Q-mod1
EDFA
EDFA
EDFA
EDFA
EDFA
DL
PBC
DEMUX
1
2
3
4
p/2
f
PAM-to-QAM converter
PAM-to-QAM
1
2
3
4
1 2 3 4
ba xx dc xx
ba xx dc xx
-60
-50
-40
-30
-20
193.79193.85496193.91992193.98488194.04984
Frequency [65GHz/div]
193933.75
Power[10dB/div]
Nyquist-Shaped Single-
Carrier 124 GBaud
PDM-32QAM
ECL MZM
32.5 GHz
1545.72nm
EDFA
10 MHz
Delay Line
DL
DL
I/Q-mod2
TX DSP
I/Q-mod3
I/Q-mod4
DAC
I/Q-mod1
EDFA
EDFA
EDFA
EDFA
EDFA
DL
DEMUX
1
2
3
4
p/2
f
PAM-to-QAM conv
PAM-to-QAM
1
2
3
4
1 2 3 4
ba xx dc xx
ba xx dc xx
[5] R .Rios-Müller et al, ”1-Terabit/s Net Data-Rate Transceiver
Based on Single-Carrier Nyquist-Shaped 124 GBaud PDM-32QAM.”
OFC’15 Post-deadline Th5B-1

33
1 Terabit/s signal based on sub-band transmitter
2
4
6
8
10
20 25 30 35 40
Q²-factor[dB]
OSNR [dB/0.1 nm]
16QAM
32QAM
124 GBaud
1.24 Terabit/s
Line rate
First Nyquist-Shaped 124 Gbaud PDM-32QAM demonstration
[5] R .Rios-Müller et al, ”1-Terabit/s Net Data-Rate Transceiver Based on Single-Carrier Nyquist-Shaped 124
GBaud PDM-32QAM.” OFC’15 Post-deadline Th5B-1

34
Agenda
6. Conclusion

35
Conclusion
FEC
FLEX
NL
• Still some margin for improvement
• Spatially-coupled LDPC can provide near-Shannon performance
• Fine tune performance with new degrees of freedom
• Ex: Bitrate, channel spacing, FEC OH, etc
• Performance increase shown experimentally
• Backpropagation still too complex
• Alternatives reduce complexity with small perf. loss
Beyond
400 Gb/s
• Steady increase of bitrate per channel
• 1 Terabit/s

36
References
• [1] R. Rios-Müller, et al. "Optimized spectrally efficient transceiver for 400-Gb/s single
carrier transport.“ ECOC’ 14, PD.4.2
• [2] A. Ghazisaeidi, et al. "52.9 Tb/s transmission over transoceanic distances using adaptive
multi-rate FEC.“ ECOC’14 , PD.3.4
• [3] L. Schmalen, et al. "Evaluation of left-terminated spatially coupled LDPC codes for
optical communications." ECOC’14 , Th.2.3.4
• [4] J. Renaudier. et al ”Experimental transmission of Nyquist pulse shaped 4-D coded
modulation using dual polarization 16QAM set-partitioning schemes at 28 Gbaud” OFC’13
(OTu3B-1)
• [5] R .Rios-Müller et al, ”1-Terabit/s Net Data-Rate Transceiver Based on Single-Carrier
Nyquist-Shaped 124 GBaud PDM-32QAM.” OFC’15 Post-deadline Th5B-1

37
Questions
Rafael.Rios_Muller@alcatel-lucent.com

Next-Generation High-Capacity Submarine Transmission

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