All-Optical Regeneration of Phase-Encoded Signals in ... · 2-1. DPSK Regenerator Using a...

1WC3.2 Matsumoto / 27

M. Matsumoto

Graduate School of EngineeringOsaka University

2010 IEEE Photonics Society Summer Topical Meetingon Nonlinear Fiber Optics

July 19-21, 2010

All-Optical Regeneration of Phase-EncodedSignals in Transmission Systems


Outline

◆ Introduction

◆ Summary

◆ (D)BPSK signal regeneration

◆ (D)QPSK signal regeneration

◆ Discussion


Introduction Demand for cost-effective high-capacity transmission is increasing.

◆ Higher symbol rates are beingused.

◆ Advanced modulation formats having high spectral efficiencyare being introduced.

and/or , ...

time

Re

Im

Transmission distance is limited by noise accumulation togetherwith nonlinear and linear signal impairments.

Long-distance systems may need signal regenerators.

TX RX TX RX TX RX

It is desired that some or all of the electrical regenerators arereplaced by all-optical regenerators.


Introduction

Issues

All-optical regenerators

higher-speed operation lower-power consumption less format-dependent operation

are expected.

◆ Regeneration of signals in advanced modulation formats(QPSK, 8PSK, QAM,....) is yet to be explored.

◆ Regenerators accept only signals meeting predeterminedconditions (pulse width, chirp,...).

◆ DEMUX/MUX are needed in general for regeneration ofWDM signals.


Regeneration of PSK signals

Regeneration of PSK signals needs regeneration of amplitudeand phase or two quadrature components (two dimensions).

Regeneration of OOK signals is simple.

Pout

Pin

1. Phase-preserving amplitude regeneration2. Phase and amplitude regeneration using PSK to OOK

demodulation and amplitude regeneration3. Phase and amplitude regeneration using saturated phase-

sensitive amplifier4. Noise averaging between adjacent symbols

Schemes of (D)BPSK signal regeneration


1. Phase-Preserving Amplitude Regeneration

phase-preservingamplitude regeneration

transmission overnonlinear fiber (SPM)

Phase noise after the transmission over nonlinear fiber is reduced.

Saturation of four-wave mixing in fiber M.Matsumoto, PTL17,1055(2005) Asymmetric NOLM A.G.Striegler et al.,PTL17,639(2005), K.Cvecek et al.,PTL19,146(2007) Semiconductor saturable absorber Q.T.Le et al.,PTL22,887(2010)


2. Phase and Amplitude Regeneration UsingAmplitude-Only Regenerator

Phase modulation

Amplitude modulation

Amplituderegenerator

Amplitude information is transformed back to phaseinformation.

Demodulation using delay interferometer

Coherent demodulation

(Amplitude noise is removed.)

DPSK OOK

BPSK

OOKLocalOscillator


2-1. DPSK Regenerator Using a Straight-LinePhase Modulator

2R amplituderegenerator

All-optical phase modulator

input output

1-bit DI

CR / Opticalpulse source

λs λs+ Δλ

Clock recovery / Optical pulse source

1-bit delayinterferometer

x N

λ'sλ's

HNLF

HNLF

Phase modulator

Amplitude regenerator

Strength of the 2R amplitude regenerator > 6.5dB

M. Matsumoto, PTL17, 213 (2007).


Experimental Setup

• 10Gb/s DPSK signal regeneration

• Two-stage Mamyshev regenerator in bidirectional configuration is used.

• Mode-locked semiconductor laser (MLLD) is used as a clock source.

• XPM-based all-optical phase modulation is used.

HNLF1: D=-0.35ps/nm/km γ ~12/W/km L=1.8km

M. Matsumoto and H. Sakaguchi, OE16, 11169 (2008)M. Matsumoto and Y. Morioka, OE17, 6913 (2009)


Experimental Result

Waveforms in the regenerator

input signal (A) OOK signal after DI (B)

OOK signal after 2R (C) output signal (D)

HNLF: D=2.2ps/nm/km γ ~12/W/km L=2.4km

Δλ=4.5nm, walkoff time =24ps


Transmission Experiment

DPSKTX

DPSK signalregenerator

DPSKRXATT1

DDM fiber (DSF) 40km SMF (50km)+DCF

Ps

ATT2

Transmission experiment at 10Gb/s

Signal before the regenerator is degraded either by nonlinearity(when Ps is large) or by ASE (when ATT1 is large).


Experimental Result

Signal before regeneration is degraded by nonlinearity.

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

0.0001

0.001

0.01

-40 -35 -30 -25 -20 -15

BE

R

received power Prec (dBm)

after 2nd span

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

0.0001

0.001

0.01

-40 -35 -30 -25

BE

R

received power Prec (dBm)

after 1st span

regenerator not insertedregenerator inserted

-- Ps=8dBm-- 9.5dBm-- 11dBm

regenerator not insertedregenerator inserted

-- ATT2=8dB-- 14dB-- 18dB

Ps=9.5dBm


2-2. DPSK Regenerator Using a Mach-ZehnderInterferometer Modulator

• Complementary OOK signals drive all-optical modulators in MZI.

• All-optical modulators in MZI can be either phase or amplitudemodulators.

outputCR / Opticalpulse source

All-optical modulator


1-bit DI

DPSK

OOK

OOK

!

Ain exp(" in )

!

Aout exp("out )

I. Kang et al.,Th4.3.3,ECOC2005 (2005)P. Vorreau et al.,PTL18, 1970 (2006)Ch. Kouloumentas et al.,OMT5, OFC2010 (2010)


Requirements for the ModulatorsAdditional 2R regenerators are needed either before or after the DIfor suppression of both phase and amplitude noise.

outputCR / Opticalpulse source

Phase modulator

Phase modulator

1-bit DI

Phase-preserving2R regenerator

2R regenerator

2R regenerator

(Strength of the amplitude regenerator > 0.46 dB)

Amplitude modulators instead of phase modulators can be used.

Saturation behavior of the modulators may make the 2R amplituderegenerators unnecessary.

R. Elschner et al., OL32, 112 (2007)R. Elschner et al.,ThP3, 2007LEOS Annual Meeting (2007)

J. Wang et al., OE17, 22639 (2009).


Logic Alteration and its Recovery

Dcn dn=cn ⊕ dn-1

DPSK regenerator using DI forDPSK --> OOK demodulation

bn=an ⊕ an-1D

=

bk ・・・ 0 1 1 0 1 0 1 1 1 0 1

0 π π 0 π 0 π π π 0 π（phase ）（phase

time

ak ・・・ 0 0 1 0 0 1 1 0 1 0 0 1

0 0 π 0 0 π π 0 π 0 0 π ）

time

Demodulation by DI alters data logic.(Phase difference absolute phase)

The logic alteration can be recovered by pre/post-coding.

I. Kang et al.,Th4.3.3,ECOC2005 (2005)P. Vorreau et al.,PTL18, 1970 (2006)


2-3. BPSK Regenerator Using Coherent DemodulationDemodulation from DPSK to OOK by DI may be replaced bycoherent demodulation.

2R

phasemodulator

input output


Localoscillator

Coherent demodulation can be similarlyused in the MZI-based regenerator.

Required strength of 2R may be halved.Logic of the signal is preserved.◆ Phase-locked local oscillator is needed.

1-bit DI2R

phasemodulator

input output



3. BPSK Regenerator Using Phase-Sensitive Amplifier

Degenerate nonlinear interferometer

Two-pump degenerate FWM

3dBcouplerEs Ep

Es,out

signal

pump1 pump2

ω

!

Es,out

= µEs,in

+ "Es,in

#

!

µ2

" #2

= 1( )

Phase-sensitive gain

in small-signal condition

Extraction of one quadrature component

K. Croussore et al.,OL29, 2357 (2004)K. Croussore et al.,OE14, 2085 (2006)

A. Bogris and D. Syvridis, PTL18, 2144 (2006)K. Croussore and G. Li, JSTQE14, 648 (2008)

C. J. McKinstrie and S. Radic, OE12, 4973 (2004)M. E. Marhic and C. -H. Hsia, Quantum Opt.3, 341 (1991)


Phase and Amplitude Regeneration

x G

x 1/GPhase-sensitive

gain

Phase-sensitive gainand its saturation


Recent ExperimentOFC 2010PDPC3

ωp1ωs

ω

2ωs −ωp1

ωp1ωs

ωpump seedgenerationin HNLF1

injectionlocking of

LD

ωp1

ωs

ωp2 PSAin HNLF2


Regeneration of (D)QPSK signals

1. Phase-preserving amplitude regeneration2. Phase and amplitude regeneration using PSK to OOK

demodulation and amplitude regeneration3. Phase and amplitude regeneration using saturated phase-

sensitive amplifier

Schemes of (D)QPSK signal regeneration

regenerator


(D)QPSK Regenerator Using Amplitude Regenerators

1. Regenerator using straight-line phase modulators

2. Regenerator using MZI

2Rregeneratorinput

output

phasemodulator

0 / π 0 / π/2

CR / Opticalpulse sourceθDI=π/4

θDI=-π/4

2Rregenerator

phasemodulator

input

output

CR/Pulsesource





2R

2R

2R

2R

θDI = π/4

θDI = -π/4π/2


(D)QPSK Regenerator Using Amplitude Regenerators

• Required strength of 2R amplitude regenerators is larger thanthat of DPSK regenerators.

Delay interferometers (DIs) are not operated at their maximain output power vs phase difference response.

Suppression of input phase noise is weaker.

• Logic alteration can be recovered by suitable pre/post coding atterminals.

• Coherent demodulation instead of DI demodulation can beused. (X. Yi et al., JLT28,587 (2010))


Numerical Simulation

2Rregeneratorinput

output

phasemodulator

0 / π 0 / π/2

CR / Opticalpulse sourceθDI=π/4

θDI=-π/4

2Rregenerator

phasemodulator

All-optical modulators using XPM in HNLF

Cascaded Mamyshev-type 2R amplitude regenerators

80Gsymbol/s (160Gbit/s)2.5ps RZ-DQPSK

M. Matsumoto, OE18, 10 (2010)


Numerical Simulation

-2

-1

0

1

2

-2 -1 0 1 2

Ima

gin

ary

pa

rt [

mW

1/2

]

Real part [mW1/2

]

(a)

-1.5

0

1.5

-1.5 0 1.5Im

ag

ina

ry p

art

[m

W1

/2]

Real part [mW1/2

]

(b)

-2

-1

0

1

2

-2 -1 0 1 2

Ima

gin

ary

pa

rt [

mW

1/2

]

Real part [mW1/2

]

(c)

-1.5

0

1.5

-1.5 0 1.5

Ima

gin

ary

pa

rt [

mW

1/2

]

Real part [mW1/2

]

(d)

input OSNR26 dB/0.1nm

24 dB/0.1nm

0

2

4

6

8

10

20 22 24 26 28 30 32sta

nd

ard

de

via

tio

n o

f p

ha

se

flu

ctu

atio

n (

de

g)

OSNR (dB/0.1nm)

!

"# ,input

!

"# ,output

simulation using1024 symbols


QPSK Regenerator Using Phase-Sensitive AmplifiersSaturatedphase-sensitivegain in twoquadratures

Coherentaddition

Z. Zheng et al., OC281, 2755(2008)

Phase-sensitive gain for extraction ofindividual quadrature components

+ phase-preserving multi-levelamplitude regeneration

QAM regeneration


Issues

1. Regenerators accept only predetermined-shaped pulses.

For wide acceptance of all-optical regenerators in practical systems,several issues must be addressed:

Optical dispersion compensation will be needed before theregenerator.

In some types of regenerators, pulse overlap beforeregenerators leads to inter-symbol interference.

Such ISI may be mitigated by signal processing at thereceiver such as Maximum Likelihood Sequence Estimation,while the regenerator performance is mostly retained.

Cooperative use of• all-optical regeneration and otheroptical compensation methods• electrical signal processing at terminals.

will be a future research topic.


SummaryRegeneration of phase-encoded signals has been discussed.

1. (D)BPSK-signal regeneration•Phase-preserving amplitude regenerator•Phase and amplitude regenerator using (D)BPSK to OOKdemodulation•Phase and amplitude regenerator using phase-sensitiveamplifier

2. (D)QPSK-signal regeneration•Simulation of 160Gb/s DQPSK signal regeneration usingfiber-based amplitude regenerator.

3. Issues in using all-optical regenerators in real systems

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