ISUPT 2013October 22, 2013

Ultrahigh‐speed Nyquist Pulse Transmission and 3M (Multi)

Technology

Ultrahigh‐speed Nyquist Pulse Transmission and 3M (Multi)

Technology

Masataka Nakazawa

Research Institute of Electrical CommunicationTohoku University

2-1-1 Katahira, Aoba-ku, Sendai-shi, 980-8577 Japan

OutlineOutline

(1) Technological overview of optical communication infrastructure

(2) Ultrafast and high spectral efficiency optical transmission

• 1024~2048 QAM transmission• Optical Nyquist pulse TDM transmission

(3) Multi-core fibers for SDM transmission• Mode-coupling measurements along an MCF using

a 7 channel OTDR

(4) Summary

Technological overview of optical ｆiber ｔｒansmissionTechnological overview of optical ｆiber ｔｒansmission

100M

Lin

k C

apac

ity

/ fib

er(s

) [

bp

s]

1.6G2.4G

1980 1990 2000

400M

10GTDM

Moore’s Law

2010 2020

100T

1G

1P

1E

1T

1G

1P

1E

1T

40G

WDM

10Gx80

EDFA

120

100

80

60

40

20

0

Inte

rnet

tra

ffic　

[Gb

it/s

]

Year1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Increase in Internet Traffic in Japan

1st InnovationEDFA, WDM

2nd Innovation•Multi-level coherent transmission

•Multi-core fiber•Multi-mode control

1 Tbit/s@2009

40% increase per year

100G

Optical power limitationBandwidth limitation of

optical amplifiers

Physical dimensions for modulation and multiplexingPhysical dimensions for modulation and multiplexing

WDM: Wavelength Division MultiplexingSDM: Space Division Multiplexing

Quadrature

Time

SDM

By courtesy of P. Winzer

First “M”: Multi-level modulationFirst “M”: Multi-level modulation

QAM (Quadrature Amplitude Modulation):

Two carriers with the same frequency are amplitude-modulated independently.

The phase of the two carriers is 90 deg. shifted each other.

2N QAM processes N bits in a single channel, so it has N timesspectral efficiency compared with OOK.

Constellation map for 16 (=24) QAM

0000 0100 10001100

0101 1101 10010001

11110011 0111 1011

01100010 1110 1010

rθ

同位相(I)

直交位相(Q)

In-phase (I)

Quadrature-phase (Q)

0 1

With OOK

In-phase (I)

Quadrature-phase (Q)

Challenges to 1024 and 2048 QAMChallenges to 1024 and 2048 QAM

Constellation of back-to-back signal

1024 QAM

2048 QAM

SNR requirement for FEC limit (BER = 2x10-3)

512 QAM:Eb/N0=21 dB → SNR=30.5 dB (1 Symbol =9 bit)

1024 QAM:Eb/N0=24 dB → SNR=34 dB (1 Symbol =10 bit)

2048 QAM:Eb/N0=27 dB → SNR=37.4 dB (1 Symbol =11 bit)

10 15 20 25 3010

-6

10-5

10-4

10-3

10-2

10-1

512QAM

2048 QAM

1024QAM

Eb /N0 [dB]

FEC threshold

2048 = 211

= 48 x 48 – 256= 2304 – 64 x 4

-100

-80

-60

-40

-20

0

-3 -2 -1 0 1 2 3

Po

we

r [d

Bm

]

RF frequency [GHz]

PCEDFA

IQ Mod.

(fOFS=2.03 GHz)OFS

Optical Filter (3.5 nm)

12Gsample/s

PC AttAmplifier

PC

IQ Mod.

OFS

3 Gsymbol/s 1024 QAM signal・Nyquist raised cos. filter (roll off = 0.35)・Pre-equalization with FDE(FFT size = 16384, Frequency resolution = 0.73 MHz)

PBC

XY

PC

PD

Synthesizer

FeedbackCircuit

LocalOscillator

DBM

(Tunable Fiber Laser)

PC

PC fsyn=2.03 GHz

90°Optical Hybrid75 km SLA

Digital Signal Processor

Etalon

Att Prec

A/DB-PD X

Y

Optical filter (0.7 nm)A/DB-PD

A/DB-PD A/DB-PD

90°

90°PCRaman

Pump-1 dBm

PC: Polarization ControllerOFS: Optical Frequency ShifterPBC: Polarization Beam CombinerSSMF: Standard Single-mode FiberDBM: Double Balanced MixerB-PD: Balanced Photo-Detector

Att

75 km SLA

Raman Pump -1 dBm

fQAM signal

2.03 GHz

Inte

nsi

ty

Pilot signal

C2H2 FrequencyStabilized Fiber Laser

Arbitrary WaveformGenerator

LO

Demodulation Bandwidth= 4.05 GHz

40 Gsample/s

・Linewidth: 4 kHz

・Linewidth: 4 kHz

Back propagation

(Step size : 9.375 km)

Y. Koizumi et al., Opt. Exp., 20, 12508 (2012)

Polarization-multiplexed 3 Gsymbol/s, 1024 QAM (60 Gbit/s) coherent optical transmission systemPolarization-multiplexed 3 Gsymbol/s, 1024 QAM (60 Gbit/s) coherent optical transmission system

-30 -25 -20 -15 -10

Back-to-back (X)Back-to-back (Y)After 150km transmission (X)After 150km transmission (Y)

10-5

10-4

10-3

10-2

10-1

BER

Received Power [dBm]

Back-to-back

After 150 km transmission

BER characteristics

FEC threshold

Experimental results for 60 Gbit/s 1024 QAM transmissionExperimental results for 60 Gbit/s 1024 QAM transmission

BE

R

60 Gbit/s

4.05 GHz x 1.07 = ≒ 13.8 bit/s/Hz

Spectral efficiency (single-channel)

Roll-off factor = 0.35Signal bandwidth: 3 Gsymbol/s x (1+) = 4.05 GHz

Trend in high speed, high capacity coherent transmission

Trend in high speed, high capacity coherent transmission

High-speed transmissionOTDM/ETDM

Spectrally efficient transmissionMulti-level modulation

Driving force for high-speedoptical networking100 Gbit/s Ethernet

Driving force for ultra-efficient/large capacity FTTH

OOK, DPSK, DQPSK

M-PSK, QAM, OFDM

Frequency

Time

OTDM/RZ-QAM

RZ-OTDM

QAM

Realization of high-speed, high spectral efficiency transmission

OpticalNyquist pulse transmission

= 0

= 1 = 0.5

Proposal of optical Nyquist pulse and its TDMProposal of optical Nyquist pulse and its TDM

= 0

= 1 = 0.5

Nyquist filter has a sinc-function-like impulse response with zero crossing at every symbol period Intersymbol interference (ISI) can be suppressed even in smaller bandwidth

Tf

Tf

TfT

Tf

fR

2

1||,0

2

1||

2

1,)1||2(

2sin1

2

12

1||0,1

)(

T: Symbol period: roll-off factor

Interleaving of Nyquist pulseOptical Nyquist pulse (Impulse response of Nyquist filter)

2)/2(1

)/cos(

/

)/sin()(

Tt

Tt

Tt

Tttr

Nyquist filter

Nyquistfilter

Baseband data signal(QPSK, QAM, …)

f f+fs +2fs-fs-2fs+fs-fs

tt

1/fs

t

11, 0 | |

2

1 1 1( ) 1 sin (2 | | 1) , | |

2 2 2 2

10, | |

2

fT

H f T f fT T

fT

Transferfunction:

Bandwidth limited data signal(not a “pulse”)

ffc Pulse

shaper

ffc+Nfs

fc-Nfs

t

Transform-limited optical pulses (Gaussian, sech, …)

Optical Nyquist “pulse”

2

sin( / ) cos( / )( )

/ 1 (2 / )

t T t Tr t

t T t T

11, 0 | |

2

1 1 1( ) 1 sin (2 | | 1) , | |

2 2 2 2

10, | |

2

fT

R f T f fT T

fT

Waveform:

Spectrum:

Comparision between Nyquist filtering and optical Nyquist pulses

Comparision between Nyquist filtering and optical Nyquist pulses

K. Kasai et al., OECC 2007 PDP and IEICE Electron. Express vol. 5, 6 (2008).

M. Nakazawa et al., Opt. Express vol. 20, 1129 (2012).

6.25 ps

DemultiplexerMultiplexer

Optical Fiber

MultiplexedOTDM signal

Time

25 ps

Ultrahigh-speed OTDM transmission using optical Nyquist pulses[1]

Ultrahigh-speed OTDM transmission using optical Nyquist pulses[1]

[1] M. Nakazawa et al., Opt. Express, 20, 1129 (2012).

40G 160G40G

40G

40G

40G

40G

40G

40G

Optical Nyquist pulse train

No

rmal

ized

po

wer

3.125 ps

No

rmal

ized

po

wer

160 Gbaud OTDM waveform

No

rmal

ized

po

wer

40 GHz optical Nyquist pulse( = 0.5)

Demultiplexed signal

Ultrafast optical sampling

1540 nm1.6 ps

MUX

PC EDFADemod.

EDFA

PDATT

DI

Prec40 GHzMLFL

PLL EDFA

OpticalDelay PC 15 nm

CLK

1563 nm800 fs

CLK

EDFA

HNL-DFF2 km

40 GHz

1 nm

EDFA

2 nm

40 GHzMLFL

ErrorDetector

40 GHzPPG

40 Gbit/s215-1 PRBS

Q

Q

40 G 640 Gbaud

10 nm

HNLF 100m

PC

PC

PC

EDFA

SMF50 km

PC

x7

DPSK Modulator

IDF25 km

640 Gbit/s DPSK transmitter

525 km transmission link

40 Gbit/s DPSKrecieverDFF

500 m640 G 40 Gbit/sDEMUX

EDFA 15 nm

Pulseshaper

PC PBS//

⊥

Pulseshaper

EDFA

OpticalDelay

OpticalNyquist pulse generator

10 nm

640 G 1.28 Tbit/s polarization-multiplexed

NOLM

1.28 Tbit/s/ch - 525 km polarization-multiplexed DPSK transmission with 640 Gbaud optical Nyquist pulse

1.28 Tbit/s/ch - 525 km polarization-multiplexed DPSK transmission with 640 Gbaud optical Nyquist pulse

MLFL: Mode-Locked Fiber LaserHNL-DFF: Highly NonLinear-Dispersion Flattened FiberCLK: Clock RecoveryPPG: Pulse Pattern GeneratorIDF: Inverse Dispersion Fiber

DI: Delay InterferometerATT: Optical attenuatorPD: Balanced Photo DetectorNOLM: Nonlinear Optical Loop Mirror

K. Harako et al., Opt. Express, 21, 21603 (2013).

Optical Nyquist pulse for 640 Gbaud transmissionOptical Nyquist pulse for 640 Gbaud transmission

Optical Nyquist pulse waveform and spectrum

-90

-80

-70

-60

-50

-40

-30

-20

-10

1530 1540 1550

Power [dBm]

Wavelength [nm]

0

5

10

15

20

25

Power [

mW]

Time [ps]1.56 ps/div

Growth of depolarization-induced crosstalk

0

0.02

0.04

0.06

0.08

0.1

0 100 200 300 400 500 600

Crosstalk

Transmission Distance [km]

4 dB

Gauss

Nyquist

L2 fitting

For 640 Gbaud• Due to narrower spectral width of the

Nyquist pulse, the growth rate of the depolarization-induced crosstalk is much lower than a Gaussian pulse.

• Crosstalk was 4 dB lower than that of a Gaussian pulse after 525 km propagation.

1.28 Tbit/s/ch-525 km polarization-multiplexed transmission experiments

1.28 Tbit/s/ch-525 km polarization-multiplexed transmission experiments

-32 -30 -28 -26 -24 -22 -20 -18

Bit Error Rate

Received Optical Power [dBm]

10-10

10-3

10-4

10-5

10-6

10-7

10-8

10-9 Single-pol

Pol-MUX

Back to

back

Optical Nyquist pulse Gaussian pulse

-32 -30 -28 -26 -24 -22 -20 -18

Bit Error Rate

Received Optical Power [dBm]

10-4

10-5

10-6

10-7

10-8

10-9

10-10

10-3

Back to

back Single-pol

Pol-MUX

1530 1540 1550 1560

10dB/div

Wavelength [nm]

Gauss (600 fs) signal

crosstalk

1525 1535 1545 1555

10dB/div

Wavelength [nm]

Nyquist (640 Gabud)

crosstalksignal

Spectral efficiency: 1.28 Tbit/s960 GHz x 1.07( = 0.5)

= 1.25 bit/s/Hz for DPSK (Typical SE is 0.5 bit/s/Hz for DPSK)

225 m150 m200 mCladding diameter

12719# of cores

H. Takara et al. (NTT, Fujikura, Hokkaido Univ., DTU), ECOC2012, Th3.C.1.

T. Hayashi et al. (Sumitomo), OFC2011, OWJ3, PDPC2.

J. Sakaguchi et al. (NICT, Furukawa, Optoquest), OFC2012, PDP5C.1.

Reference

0.199 dB/km0.18 dB/km0.23 dB/kmLoss

-55~-49 dB/km- 92 dB/km- 42 dB/kmCrosstalk

80 m2

45 m

88 m272 m2Aeff

37 m35 mCore pitch

Multi-core fibers for SDM transmissionMulti-core fibers for SDM transmission

Space-division multiplexed transmission using MCFSpace-division multiplexed transmission using MCF

D. Qian et al. (NEC America, Corning, etc.), FiO2012, FW6C.3.

H. Takara et al. (NTT, Fujikura, DTU, Hokkaido Univ.), ECOC2012, Th3.C.1.Ref.

3 km52 kmDistance

Spatial optical coupling

1.05 Pbit/s (195 Gbit/s x 385 WDM x [12 core (PDM-32 QAM) + 2 mode (PDM-QPSK)])

Fan in/fan out deviceMCF coupling

1.01 Pbit/s (456 Gbit/s PDM-32QAM x 222 WDM x 12 core)

Total Bit rate

Mode coupling measurement along MCF using multi-channel OTDR[1]

Mode coupling measurement along MCF using multi-channel OTDR[1]

12

34

56

7

Time

Optical pulse

Pulse width:

Input power: P0

Pbs1Pbsm

MCF

Fiber length

Backscattered power

Pbs1

Pbs2 Pbs3

Pbsm / Pbs1

KSlope: 2h1,m

Local mode coupling due to structural imperfection

Fiber length

)(

)(

1,1

1,1111

mmmmm

mm

PPhPdz

dP

PPhPdz

dP

Mode coupling between core 1 and core m:

KLhP

Pm

bs

bsmm ,1

1,1 2

From Pbsm/Pbs1, mode coupling coefficient h1,m and its longitudinal variation can be measured[2] .

[1] M. Nakazawa et al., Opt. Exp., 20,12530 (2012), [2] M. Nakazawa et al., JOSAA, 1, 285 (1984).

Mode coupling measurement resultsMode coupling measurement results

Original backscattered signals

Mode coupling ratio from center to outer cores

0.20 dB/km

(Input: Center core)

Mode coupling coefficient

2.9 kmLength

217 mCladding

diameter

46 mCore pitch

MCF under test

M. Nakazawa et al., OFC2012, OTh3I.3

Mode-division-multiplexed transmission using MIMOMode-division-multiplexed transmission using MIMO

Q

kk tntxhty

1

)()()(Receivedsignal

x(t): Input signal, n(t)：Noise, Q：Number of modes

Distortion in mode k: kcjkkk eah

(1) SISO (Single Input Single Output) (One Tx, One Rx)

ak: Loss of mode kk: Group delay of mode kk: Coupling ratio to mode k

(2) MIMO (Multiple Input Multiple Output) (M Tx, N Rx)

hijk: Distortion when transmitted from Tx j to Rx i via mode k

Received signal at Rx i

)()()( ttt nHxy Matrix representation Estimate H from x(t) and y(t)

NitntxHtntxhtyM

jijij

M

j

Q

kijijki 1,)()()()()(

11 1

Tx 1

Tx 2

Tx M

Rx 1

Rx 2

Rx N

。。。

。。。

Mode 1

Mode 2 Mode ｋ

Mode multiplexer / demultiplexerMode multiplexer / demultiplexer

Free space opticswith phase plates[1]

Fiber coupler[2]

LCOS(Liquid Crystal on Silicon)[3]

[1] S. Randel et al., Opt. Exp. 19, 16697 (2011).[2] N. Hanzawa et al., OFC2011, OWA4.[3] C. Koebele et al., Opt. Exp. 19, 16593 (2011).

Mode-division-multiplexed transmission experimentsMode-division-multiplexed transmission experiments

5 modes x 100 Gbit/s - 40 km PDM-QPSK transmission using LP01 + LP11a + LP11b + LP21a + LP21b (2x2 MIMO + 4x4 MIMO + 4x4 MIMO)[1]

6 modes x 40 Gbit/s - 130 km PDM-QPSK transmission using LP01+LP11a+ LP11b+ LP21a+ LP21b+ LP02 (12x12 MIMO)[2]

[1] C. Koebele et al. (ALU), ECOC2011, Th.13.C.3.[2] R. Ryf et al. (ALU), FiO2012, FW6C.4.

SummarySummary

Recent advances toward the realization of an ultrahigh SE and ultrahigh-capacity SDM transmission are presented with a special focus on the following novel technologies:

1. Ultramulti-level coherent transmission up to 1024 levels

2. Ultrafast coherent pulse transmission with OTDM RZ/QAM

3. Nyquist pulse transmission

4. MCF characterization with longitudinal mode-coupling measurement

Fiber capacity at a Pbit/s level is expected to be achieved with SDM by taking full advantage of the high spectral efficiency and high spatial density in MCF.