recent advances and trends for digital coherent 100gb/s ... watch and sps... · page 3 . nec...

NEC Corporation www.nec.com/submarine/

Yoshihisa Inada Submarine Network Division

NEC corporation

Recent advances and trends for digital coherent 100Gb/s and beyond technologies in submarine optical cable

OFC MARKET WATCH Panel 2

NEC Proprietary Page 2

▐ Introduction

▐ 100G submarine cable systems

▐ Innovative technologies for beyond 100G systems

▐ Summary

Outline

NEC Proprietary

▐ Recent growth of international traffic demand has driven a drastic capacity enhancement of trans-oceanic submarine cable systems supported mostly by the break-through of digital coherent technologies with large spectral efficiency.

▐ The introduction of 100G/s technology has stimulated the investment for new build systems as well as capacity upgrade of legacy systems as it can deliver large capacity in a more cost-effective way.

▐ Recent advances and trends in submarine industry are presented and discussed based on our records and activities.

Introduction


4th Generation (Digital Coherent)

Year

Cap

acity

(Bit/

s) /

Fibe

r Pai

r

2nd Generation (DWDM)

3rd Generation (Multi-level formats)

'98 ‘00 ‘02 ‘04 ‘06 ‘08 ‘10 ‘12 ‘14 ‘16 ‘18 ‘20

1T

10T

100G

10Gb/s System Based

10G x 192 10G x 128 10G x 96 10G x 64 10G x 32 10G x 16

40Gb/s System Based

40G x 88 40G x 64

40G x 176

100G x 100

100Gb/s System Based

beyond-100Gb/s 400G

1st Generation (WDM)

5G

1T 5th Gen.

(Super Channel) O

ptic

al

Reg

ener

ator

2.5G x 16

'96 '94

2.5G x 8

5G

Opt

ical

Am

plifi

er

Tun.

DC

M

Tun.

Las

er

You are here

Evolution of Capacity and Technologies

NEC Proprietary

Transmission Distance (km)

Capacity/fp

3,000km 6,000km 9,000km

5Tbps

10Tbps

20Tbps

12,000km

Technology Trend for 100G and Beyond

100G DP-BPSK [legacy cable] 100GHz spacing

100G DP-QPSK 50GHz spacing

Multi-carrier (Super-channel) 400G DP-16QAM

400G/1T DP-QPSK Superchannel

Technologies • SD LDPC FEC • Higher order modulation • Nyquist/ Super-channels • NL compensation • Advanced Fiber


▐ Introduction



▐ Summary

Outline

NEC Proprietary

Submarine cable

Repeater

Line terminal equipment

Branching unit Power feeding

equipment

Components for Submarine Cable System

NEC Proprietary

Advanced Components for 100G Submarine System

Equipment Applied Key Technologies

SLTE Multi-level modulation (BPSK, QPSK, 16QAM) Polarization multiplexing and demultiplexing Digital coherent detection Digital compensation for linear effect (CD, PMD) Error Correction (LDPC based soft decision FEC)

Cable Low loss and Large Effective Area fiber Uncompensated dispersion map

Repeater Er-doped fiber amplifier (same as 10G/40G system) Increased output power Flat and wide gain characteristics

NEC Proprietary

Digital-Coherent Technology

►Unmatched sensitivity ►Hybrid Mixer Chip by PLC

►Tunable lasers ►Narrow linewidth

Coherent Receiver ►Digital Adaptive Impairment Compensation

► Polarization-mode dispersion ► Ultra-large Chromatic dispersion compensation

►Digital polarization demultiplexing (increased SE) ►Advanced SD-FEC

LSI digital signal processing

CDC Pol-Demux Phase recovery

DSP stages (100GbE)

Mixer

AD

C Digital

Signal Processing

01110010000101101001011

SD-FEC

11010111010101110011001

00010001111011001110010

01111100010011110011111

V1 V2 V3 V4 V5 V6 V7

C1 C2 C3

Modulation Format

Channel Spacing

SE [b/s/Hz]

Carriers Optical

Spectrum Constellation Map

100G DP-QPSK

50GHz 2 1 50GHz

X-pol Y-pol

Im Im

Re Re

X-pol

Y-pol

NEC Proprietary

LDPC Decoding Process

LDPC based Soft Decision FEC

▐ First generation: Reed-Solomon (RS) FEC

▐ Second generation: Concatenated hard-decision FEC

▐ Third generation: Soft-decision FEC with iterative decoding (Large NCG > 10dB)

Bit

Err

or R

ate

Required OSNR

Target BER

Coding Gain

+0.98 -0.89 -1.19 +0.95 -0.56 -1.04 +0.84 -0.68 +0.99 +1.23 -1.04 +0.92 +1.23

+1 -1 -1 +1 -1 -1 +1 -1 +1 +1 -1 +1 +1

Log-likelihood ratio(LLR) calculation

Converged LLRs

V1 V2 V3 V4 V5 V6 V7

C1 C2 C3

NEC Proprietary

DP-QPSK: High Capacity and Long Reach

▐ Short-medium reach upgrades and transoceanic new builds ▐ Dual polarization + Quadrature phase keying provides high

spectral efficiency [2 bit/Hz/s - 2.67 b/s/Hz] ▐ Ultra-large dispersion compensation capabilities in the DSP

processor (up to 12,000km)

DP-QPSK

6 7 8 9

10 11 12 13

6000 7000 8000 9000 10000 11000 Distance (km)

Q v

alue

(dB

)

Uncompensated Link

[ps/

nm]

[km]

Uncompensated [Large core fiber]

NEC Proprietary

DP-BPSK: Robustness against Fiber Nonlinearity

BPSK provides maximum robustness against phase noise

DP-BPSK DP-QPSK

4

6

8

10

12

14

-8 -6 -4 -2 0 2 4 Channel Power [dBm]

Q [d

B]

▐ Ultimate performance for transoceanic 100G upgrades ▐ Dual polarization + Binary phase keying provides strongest

tolerance to nonlinear effects in D+/D- submarine links DP-BPSK

Dispersion Compensation

Channels travel at same speed

Large XPM

Severe Phase-noise

NEC Proprietary

Fiber Technology C

apac

ity/R

each

SMF [0.5 dB/km]

DSF [0.3 dB/km]

DMF [0.2 dB/km]

D+ [0.16 dB/km] EDFA

Digital Coherent

Single channel

DWDM

80s 10s 90s 00s

10G DWDM 2.5G DWDM

5G

40G DWDM

100G DWDM

NZ-DSF [0.2 dB/km]

NEC Proprietary

Repeater Technology

20s 10s 90s 00s

7dBm [5-10nm]

12dBm [>20nm]

15dBm [>30nm]

5dBm [2-5nm]

1480nm Pumps 980nm Pumps

18dBm [>35nm]

Analog

Digital Coherent

OOK DPSK

40G DWDM 100G DWDM 400G/1T DP-QPSK Nyquist QAM

>20dBm [>40nm]

10G DWDM 5G~2.5G WDM


▐ Introduction



▐ Summary

Outline

NEC Proprietary

Repeater Bandwidth [nm]

FEC-NCG

Fiber Core Area [µm2]

Fiber Cores

CD-PMD SPM XPM

Spectral Efficiency Impairments Compensated

1

2

3

2

4

8

16

1 3 5 7

80

100

120

140

40

60

80

11 11.5 12

C C+L Raman

100G DP-QPSK, SSMF, C-EDFA

120

Multi-level Modulation

Key Technologies for Increasing Fiber Capacity

NEC Proprietary

30.3 km Type II fiber

20LDs50 GHz

IQ Mod

50 GHz

AWG3

IQ Mod

AWG4

IQ Mod

20LDs

AWG2

IQ Mod

OSA

PCWaveShaper

LO

PM-EDFA

ADC&

Off-lineDSP

Processing

30.3 km Type I fiber

× 7

SW

10:90

WaveShaper

PC

AWG1

10:90

OSA

Data1 LDPC

Data2 LDPC

Data3 LDPC

Data4 LDPC

12.5GHzF.S. PolMux

PolMux

12.5 GH

z IL

OTF190°

Hybrid

(a)

(b)

(c)

LSPC

2000 4000 6000 8000 100004

4.55

5.56

6.57

7.58

8.59

9.5

Transmission Distance (km)

Q (d

B)

CDCNLC

Error free transmission for 40 Channels Q versus distance

40×117.6 Gb/s PDM-16QAM OFDM Transmission over 10,181 km with Soft-Decision LDPC Coding

and Nonlinearity Compensation

Spectral Efficiency 1: Higher Order QAM

1545 1547 1549 1551 1553 15552

3

4

5

6

wavelength (nm)

Q (d

B)

CDCNLC

A B

Im

Re Re

Im QPSK 16QAM

2bit/symbol 4bit/symbol

Re

Im 8QAM

3bit/symbol

Number of bit per symbol can be increased

Baud-rate per channel can be relaxed Spectral efficiency can be increased Digital processing is required in

transmitter

OFC 2012, PDP5.C.4

NEC Proprietary

Current WDM Super-channel Concept

▐ Optical super-channels enable; 400G and beyond signals with practical electronics Reduced channel spacing with digital pulse shaping and other technologies

▐ Next generation equipment will be based on both QAM and super-channel technologies.

Spectral Efficiency 2: Super-channels

NEC Proprietary

Next Generation FEC

1) 40×117.6 Gb/s PDM-16QAM OFDM Transmission over 10,181 km with Soft-Decision LDPC Coding and Nonlinearity Compensation. OFC 2012, PDP5.C.4 2) High Capacity Field Trials of 40.5 Tb/s for LH Distance of 1,822 km and 54.2 Tb/s for Regional Distance of 634 km, OFC 2013, PDP5.A.4

▐ Adaptive overhead for on-demand performance Spectral efficiency is optimized to line

OSNR Latency can be reduced

▐ High performance LDPC Low Q limit < 5dB Still large complexity


Compensation of Fiber Nonlinearity ▐ Optical fiber nonlinearity limits the maximum Q factor after transmission. ▐ Back-propagation algorithm can compensate the fiber nonlinearity. ▐ Approx. 1dB improvement was obtained in 100Gb/s-10,000km transmission.

Analog to

Digital

Digital “Back” Propagation

DSP domain (virtual fiber)

PD PD PD PD

90 degree hybrid Tx

Optical “Forward” Propagation

Physical domain (real fiber)

Data In Data Out

Virtual Link Optical Link

Power (dBm)

Q (d

B) Limited

by OSNR Nonlinearity

(SPM)

0 0.5 1 1.5

9

9.5

10

10.5

Power/channel (dBm)

Q (d

B)

CDCNLC

1dB

NEC Proprietary

-7 -6 -5 -4 -3 -26

6.5

7

7.5

8

8.5

9

Power

Q (d

B) f

rom

BE

R127 Gb/s, L=6455 km

▐ Experimental Tests on Dispersion managed systems with back-propagation NLC algorithm SMF+DCF link DMF link NZ-DSF link

-8 -6 -4 -2 0 27

8

9

10

11

12

Power/channel (dBm)

Q (d

B)

Residual Dispersion ∼ 7400 ps/nm (y-pol)

NEC-BP=OFFNEC-BP=ON

SMF+DCF link DMF link

-10 -9 -8 -7 -6 -5 -4 -3 -2

5

6

7

8

9

10

Power/channel (dBm)

Q (d

B) [

from

BE

R]

CD CompensationNL Compensation

w/o 10G

w 10G

NZ-DSF link

Compensation of Fiber Nonlinearity (Dispersion managed links)

1) Nonlinearity compensation using very-low complexity backward propagation in dispersion managed links. OFC2012, OTh3C4 2) 100G upgrade over legacy submarine dispersion-managed fiber link using fiber nonlinearity compensation and maximum-likelihood…, OFC2012, OTu2A 3) Low Complexity Nonlinearity Compensation for 100G DP-QPSK Transmission over Legacy NZ-DSF Link with OOK channels, ECOC2012, Mo1C5


▐ Multi core fiber Capacity increase in proportion to the

number of core. Multi core EDFA is required for practical

deployment.

Multi core fiber

First demonstration of MC-EDFA-Repeatered SDM Transmission of 40×128-Gb/s PDM-QPSK Signals per Core over 6,160-km 7-core MCF, Opt. Exp, 21,789.

6,100km transmission over 7-core fiber

Space-division Multiplexing by New Fibers


Outline

▐ Introduction



▐ Summary

NEC Proprietary

Summary

▐ Thanks to the advancement in digital coherent 100Gb/s technologies and the transmission optical fiber, the deployment of 100Gb/s is underway in many projects for trans-oceanic submarine cable systems.

▐ The adoption of 100Gb/s DWDM in submarine networks significantly

increases fiber capacity in a cost-effective way.

▐ 100Gb/s technologies can be also applied to legacy systems for efficient capacity upgrades.

▐ Advanced key technologies, including FEC, nonlinearity compensation,

digital multi-level modulation or optical super-channel, will enable larger capacity of submarine cable systems beyond 100Gb/s.

recent advances and trends for digital coherent 100gb/s ... watch and sps... · page 3 . nec...

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