Next-Generation High-Capacity Submarine Transmission

1

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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

DEM

UX M

UX 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

Spectr

al eff

icie

ncy

(log s

cale

, 5dB/div

)

5Gb/s

10Gb/s

40Gb/s

100Gb/s

200Gb/s250Gb/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

Capacit

y (

Tb/s)

per

fiber

Year

50Tb/s

10Gb/s

Coherent detection

1

01

01

01

0

H

HH

HH

HH

H

H conv

-75

-65

-55

-45

-35

1528 1538 1548 1558 1568 1578 1588 1598

Pow

er

[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 1547Wavelength (0.1nm/div)

Pow

er (5

dB/d

iv)

“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

FLEX FEC

1E-16

1E-14

1E-12

1E-10

1E-08

1E-06

0.0001

0.01

1

0 5 10 15 20

Bit

err

or

rati

o

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

FLEX FEC

1E-16

1E-14

1E-12

1E-10

1E-08

1E-06

0.0001

0.01

1

0 5 10 15 20

Bit

err

or

rati

o


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

Ne

t co

din

g ga

in [

dB

]

FEC overhead [%]

Methods

NL

FLEX FEC

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

FLEX FEC

1E-16

1E-14

1E-12

1E-10

1E-08

1E-06

0.0001

0.01

1

0 5 10 15 20

Bit

err

or

rati

o


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

FLEX FEC

[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

FLEX FEC

[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

Ne

t co

din

g ga

in [

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 [%]

Req

uir

ed O

SNR

[d

B/0

.1n

m]

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

l0

3dB

I/Q mod

DAC

0, 33, 67 and 100%

pre-emphasis

-16

-12

-8

-4

0

-40 -20 0 20 40P

ow

er …

Frequency [20GHz/div]

Po

we

r [1

0 d

B/d

iv]

Po

we

r [1

0 d

B/d

iv]

Po

we

r [4

dB

/div

] 33%

67%

100%

Driver

WaveshaperEDFA

Methods

NL

FLEX FEC


18



Agenda






6. Conclusion

19



Flexibility, why?

2000

3 4 5 6 7 8 9

Reach (

km

) @

4.1

0-3

BER

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

FLEX FEC

[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

) @

4.1

0-3

BER

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

FLEX FEC

[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-f

acto

r[dB]

Wavelength[nm]

Methods

NL

FLEX FEC

[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-f

acto

r[dB]

Wavelength[nm]

Methods

NL

FLEX FEC


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-f

acto

r[dB]

Wavelength[nm]

25

30

35

40

45

50

55

1 2 3 4 5 6 7 8 9 10 11 12

Capacit

y p

er

fiber

[Tb/s

C+ L

band]

Number of bitrates

Methods

NL

FLEX FEC


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

FLEX FEC

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

X FFT FFT-1

i⅟2β2ω2h |·|2 FFT X

H(f)

FFT-1 X

(⁸⁄₉)κγheffP

e(i·)

X

input output

x M

Methods

NL

FLEX FEC

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

tnmnmtH

ntV

mtH

nmtV

ntV

mtVH

t

H

t

N

Nm

N

Nn

H

tnmnmtV

ntH

mtV

nmtH

ntH

mtHH

t

H

t

nCxxxxxxxy

nCxxxxxxxy

,

**

,

**

Methods

NL

FLEX FEC

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- f

acto

r [d

B]

Power [dBm]

3

4

5

6

1548.5 1549.5 1550.5 1551.5

Q2-f

acto

r [d

B]

Lambda [nm]

6600 km

FEC limit

Methods

NL

FLEX FEC

6000 km


3

4

5

6

13 14 15 16 17

Q2

- fact

or

[dB

]

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

FLEX FEC

25

30

35

40

45

50

55

1 2 3 4 5 6 7 8 9 10 11 12

Capacit

y p

er

fiber

[Tb/s

C+ L

band]

Number of bitrate


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

FLEX FEC

NL FLEX FEC + +

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

EDFADL

PBC

DEM

UX

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]

193933.75Pow

er [

10dB/d

iv]

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

EDFADL

PBC

DEM

UX

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

[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-

facto

r [d

B]

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

[email protected]

Next-Generation High-Capacity Submarine Transmission

Technology

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