24 Gbit/s Synthesis of BPSK signals via Direct 24 Gbit/s Synthesis of BPSK signals via Direct Modulation of Fabry-Perot Lasers under Injection

Lockingg

R. SlavíkR. Slavík11, , J. KakandeJ. Kakande22, R. Phelan, R. Phelan33, J. O’Carroll, J. O’Carroll33, B. Kelly, B. Kelly33, , and D. J. Richardsonand D. J. Richardson11

1. Optoelectronics Research Centre, University of Southampton, Southampton, UK

yy

2. Bell Labs, Alcatel-Lucent, Holmdel, NJ, USA3. Eblana Photonics Ltd., Dublin, Ireland

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Phase and amplitude encoded signalsPhase and amplitude encoded signals

QQBinary (BPSK)

QQuadruple (QPSK): Eight PSK (8-PSK):

M-level Phase-Shift-Keyed (M-PSK):

11

I

01

Q

10

Q 010110

111I

001

011Q

I

1000 101100

000

Quadrature-Amplitude Modulation (QAM):p ( )

1101

QQuadruple (4 QAM): 16-QAM:

Q

I

1000

I

2Advantage:  Higher spectral efficiency.

Generation of PhaseGeneration of Phase--modulation and QAMmodulation and QAMd t

CW laser

-+

BPSK data-data

MZ amplitude modulator

Single modulator generatesBPSK:

I data

-+ QPSK

QPSK

MZ amplitude modulator

CW laser

+

Q data-+90 deg

phase shiftphase shift

I data16 QAM

Dual‐nested (IQ)modulator for any format:

CW laser

I data

-+

Q data+

16 QAM

16 QAM

3

CW laser Q data-+90 deg

phase shift

QAM modulation penetrates Long haul and Metro and is expected to move

Our MotivationOur Motivation QAM modulation penetrates Long haul and Metro and is expected to move 

also into Access IF the cost is dramatically reduced.

C t h th t t l d l t dd l it d d t Current approach that uses external modulators add complexity and do not 

allow significant cost reduction. 

S h i f QAM f l i l bi RF h h di IQ Synthesis of QAM from multiple binary RF streams rather than direct IQ 

modulation reduces requirements on linearity and power of high‐speed RF 

circuitscircuits.

Our ApproachOur ApproachStep 1: Direct laser current modulation.

Step 2: Optical injection locking for chirp suppression and single‐frequency  

4

operation.

Step 3: Coherent addition for multiplexing and carrier suppression.

Direct laser current modulationDirect laser current modulation

High-contrast(huge chirp)

Low-contrast(for reducing the chirp)

‘1'

( g )

Q

‘1'

Q

‘0'

1I ‘0' I

Produces chirped OOK (on‐off keyed) signal.

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Cannot be multiplexed coherently with other signal.

Optical Injection Locking for chirp removalOptical Injection Locking for chirp removalRF d t

Master laserCW Slave laser

RF data

optical injection

O

W/o Injection Locking With Injection Locking(chirp-free)

OUT

‘1'

Q

(chirp free)

Injection Locking

Q

‘0' IInjection Locking

‘0'

I‘1'1

2

Chirp is removed  two points in constellation are obtained.

6

p p

Slave phase locked to the master  they can interfere together.

Wavelength Wavelength tunabilitytunability and singleand single--mode mode operation of FP laser via injection lockingoperation of FP laser via injection lockingoperation of FP laser via injection lockingoperation of FP laser via injection locking

We use Fabry‐Perot rather than single‐frequency slave lasers – injection locking can suppress the non‐injected modesg pp j

Master laserCW Slave laser

RF data

optical injection

CW

OUT

, , : Temperature-tuned

-20

0

, , : Temperature tuned

dBm

(a) Free running

-20

0

r, dB

m

(b) Injection-locked

-60

-40

Pow

er,

1520 1530 1540 1550 1560 1570

-60

-40P

ower

7

1520 1530 1540 1550 1560 1570

Wavelength, nm

1520 1530 1540 1550 1560 1570Wavelength, nm

R. Slavík et al, OFC PDP, 2013.

Coherent addition for carrier suppressionCoherent addition for carrier suppressionBy removing the carrier from OOK we get BPSK:By removing the carrier from OOK, we get BPSK:

OOK CW BPSKPrinciple:

-30

-20 InjectionLocked

dB 9 dBOOK CW BPSK

+ = -60

-50

-40

Pow

er,

No InjectionLocking

Carriersuppressed

1546.0 1546.1 1546.2 1546.3 1546.4 1546.5-70

Wavelength, nm

oc g

Master laser(CW) 2x2

Slave laser(OOK)

Binary dataCW

CW

( ) 2x2 (OOK)

Mi

OOK

CW

PS

BPSK

8

MirrorAtten.

PSCW

Coherent addition for multiplexing: QPSKCoherent addition for multiplexing: QPSKTwo BPSK phase locked to the same master are phase locked between 

them and thus can be combined to get one QPSK:

Slave laser 1(OOK)

Binarydata 1

OOK

Master laser(CW)

CW

2x2

CW

Slave laser 2(OOK)OOK

(CW)

QPSK

Binarydata 2

Phaseshifter

OUTPUTMirrorAtten.Phase

shifterOUTPUT

OOK 1

+ =1st: OOK 2

=2nd:

+CW QPSK

Principle:

9

+ = =+

Scaling: 16 QAM and beyondScaling: 16 QAM and beyond

Slave 1+2 Slave 3+4

16 QAM:

Slave 1+2 Slave 3+4

=+ =1st:

+2nd: 16 QAM

=

d

+

CW6 Q

+

Can be further scaled to 64 QAM and further

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Can be further scaled to 64 QAM and further.

Binary PSK: first demonstrationBinary PSK: first demonstration

Master laser2 2

Slave laser

Binary dataCW

CW

(CW) 2x2 (OOK)

Mirror

OOK

CW

Phasehif

BPSK

OUTPUT

MirrorAtten.

shifterCW

11R. Slavík et al, OFC 2013.

Wavelength Wavelength tunabilitytunability –– over 30 nm and over 30 nm and at up to 24 at up to 24 GbaudGbaudat up to 24 at up to 24 GbaudGbaud

Baud rate

1530 nm 1546 nm 1560 nm

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Experiment: Quadrature PSKExperiment: Quadrature PSK

Slave 1

PhaseRF Phase

shifter

2-m delayCurrent drivers 1&2 Transmitter 10 Gbit/s

2^31-1 PRBSDual output 1.2 V p-p

Bias TBias T

Slave 2Temp. drivers 1&2

shifter

1 2

3DetFeedback controller

Mirror

OSAElectrical pathOptical path

DLI OscilloscopeMaster18 dBm

Phase shifterFeedback controller Homodyne

receiverDet.

DLI Oscilloscope

3

2

R)

40

-30

-20

ensi

ty, d

Bes

.)

Two injection-locked lasers combined The above plus CW to remove the carrier

(QPSK modulation) 9 dB carrier suppression

6

5

4

-log(

BE

R

70

-60

-50

-40w

er s

pect

ral d

(0.0

1 nm

r e

Single slave w/oInjection locking(free running)

13-23 -22 -21 -20 -19 -18 -17 -16 -15

7

Power into the coherent receiver, dBm1546.0 1546.1 1546.2 1546.3 1546.4 1546.5-70

Pow

Wavelength, nm

R. Slavík et al, OFC 2013.

Various baud rates performanceVarious baud rates performanceBaud rate Propagatio EVM, amplitude,Baud rate Propagatio

n distance, km

EVM, amplitude, phase errors

14 0 19%, 13%, 8 deg14 0 19%, 13%, 8 deg

75 20%, 13%, 9 deg75 , , g

20 0 27%, 19%, 11 deg20 0

75 28%, 19%, 12 deg75

24 0 35%, 25%, 15 deg

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R. Slavík et al, OFC PDP, 2013.

Results: 16 QAM emulationResults: 16 QAM emulation16 QAM generation using 4 lasers (as shown earlier)

Slave 1+2 Slave 3+4

=+ =

2nd:

+

CW16 QAM

16 QAM generation using 4 lasers (as shown earlier):

=1st:

+ +

Slave 1 2-bitsQPSK

(a) BPSK-to-QPSK

QPSK and 16 QAM emulation by using half the number of lasers:

Slave 1delay

90 degphase shift

QPSK

(b) QPSK-to-16QAM

Slave 1+22-bitsdelay

6 dBatten.

(b) QPSK-to-16QAM

1515 Gbaud (60 Gbit/s) with EVM of 13%, amplitude error of 10%, and phase error of 9 deg. R. Slavík et al, OFC PDP, 2013.

Towards Photonic IntegrationTowards Photonic IntegrationQPSK example: We are in the process of designing a proof‐of‐principle 

PIC that we plan to manufacture within ePIXnet EU platform.

RF #114 or 28 Gbaud

RF #214 or 28 Gbaud

PD

PS

PS Laser 1

Input2 x 2

2 x 2

HRng

SOA

PDLaser 2

Output

2 x 2

2 x 1PS Mirror

R coatingAR coatin

Outline schematic of the PIC (input is an external CW laser, PS=phase shifter,

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( p , p ,PD = slow sub-MHz photodiode, SOA=semiconductor optical amplifier).

Modulation bandwidth limitationsModulation bandwidth limitationsInjection Locking can significantly enhance the modulation 

bandwidth (pictures/results taken from Lau et al, OE 2008): 

‐ Up to 80 GHz 3‐dB bandwidth demonstrated, promising in 

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p , p gprinciple operation up to 160 Gbaud.

Our new scheme for QAM synthesis from binary RF data streams can be tuned30

Summary/DiscussionSummary/Discussion

over 30 nm.

Operation demonstrated up to 24 Gbaud (QPSK) and 15 Gbaud (16 QAM)demonstrated.

EVMs for 16 QAM, QPSK and BPSK were similar, showing straightforwardscalability of this scheme to even higher modulation formats.

Injection locking can significantly enhance the laser modulation bandwidth,e.g. up to 80 GHz, promising operation of our scheme up to 160 Gbaud.

Fully suited for photonic integration.

Sponsors: EPSRC (Transforming the Future Internet: The Photonics Hyperhighway) and personal Fellowship of R S

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Sponsors: EPSRC (Transforming the Future Internet: The Photonics Hyperhighway) and personal Fellowship of R.S.