Self Coherent Detection &Reflective Modulation for

Optical Access Networks (FTTH)

Amos Agmon, Moshe NazarathyTechnion, Israel Institute of Technology

Talk given at Optical Engineering 2014Netanya, Israel

Acknowledgement: Piano+ EU Multi-National Program:Project OTONES (8 academic + industrial partners in Israel, Germany & UK )

also funded by the Israeli Chief Scientist Office

Outline

• Motivation and system design guidelines• Introduction: Optical Detection and

Motivation to Self-coherent detection• Reflective Modulation• Combining Down-Stream(DS) & Up-stream

(US)• OTONES Network design• Conclusions

2

Power dissipation of Information and Communication Equipment*

3

Shared Network Equipment~ 1 W/user

Access Network andHome Gateway:~ 10 W/user

Home Devices:~ 100 W/user

Customer Premises

* Interview with P. Vetter, Bell Labs, Sep-2010, http://www.youtube.com/watch?v=-M-9v7OdtFY

Motivation & Design Guidelines• Access Networks required to increase data throughputs

while reducing power dissipation• Designing an access-network (FTTH) allowing for low-

complexity, power-efficient Optical Network Units (ONU=Customer Premises Equipment)– Laserless, colorless low complexity ONUs– Low rate signal processing– ≥1 Gbps ONU peak Down-Stream (DS) throughput– FSAN Class B+ ODN (29 dB loss budget per Optical Distribution

Network (ODN))– Split ratio ≥ 1:64

4

5

Intro. : Optical Transmission

6

( )Id t

( )Qd t

c

( )ID

2W

c

( )QjD

2W

c

( ( ))

( )I QDjD

D

2W

0

( )

( ) ( )I Q

D

D jD

W

@ c

90 0

MZM I

MZM Q

CW Laser

doubling data throughputby means of simultaneous transmission of I & Q

Intro. : Optical Detection

7

( )Id t

( )Qd t

cos 2 ct

sin 2 ct

( )Id t

( )Qd t@ c

90 0

MZM I

MZM Q

CW Laser

LPF

LPF

Intro. : Optical Detection

8

PD

( )i t

@ c

90 0

MZM I

MZM Q

CW Laser

= LPF 2

( )Qd t

( )Id t

Intro. : Optical Detection

9

22( ) ( ) 2 Re ( ) ( )( ) LP LPcj ts t h t s t e h ti t

2*

22 * *2 2

1 12 ( ) ( ) ( )2 2

1 ( ) ( ) 2 ( ) ( ) ( )2

LP

LP

c c

c c c c

j t j t

j t j t j t j t

s t e s t e h t

s t e s t e s t e s t e h t

2( ) ( )i t s t

( )s t ( )s t

( )S

W

= LPF 2( )i t ( )i t

0

( ) ( )

( )QID jD

D

W

Intro. : Limits of Direct Detection

10

( )Qd t

2( ) ( )i t d t

( )Id t

2( )Id t

2( )Qd t

( )Q tj d

2( )Id t

0

2W

0 2W

Undetectable I-Q Mixture

2( ) ( )i t d t

PD@ c

90 0

MZM I

MZM Q

CW Laser

Solution: Coherent (heterodyne) Det.

11

( )Qd t

PD

( )Id t

2( ) ( )i t s t

c IFf c

( )S

0

( )D

W

0IFf

( )( ) ( )IFS D fL

2( ) ( )i t s t

2( ) IFj tL d t e

2L

LO

0 IFfWWIFf

2( )d t

22 2 Re (( )) IFj td ed tL tL

* ( ) IFj tL d t e 2Re

@ c

90 0

MZM I

MZM Q

CW Laser

c IFf LO

EXPENSIVE

SOLUTION

Coherent Det. drawbacks

• Complex and expensive: Tunable laser required

• Prone to frequency drifts and Phase noise, highly stable lasers required for large constellations

• Phase noise is enhanced by EqualizationCurrently, Coherent Det. is prohibitive for mass deployed communication links

12

Self Coherent Tx

13

LO mixed at Tx output:

0IFf

( ) ( )IFS D f

( )L

@ cCW

I-Q MZM

CW @ c IFf

3dB coupler locked pair

Tx

2( ) IFj tL d t e

Self Coherent Advantages

• Reduced Rx complexity: Single Photo-Diode, Laserless, colorless

• Tx Remains simple: Generating a locked pair is not hard

• Phase noise immunity: Both for Laser PN & Non-linear Self Phase Modulation (SPM)!

14

2( ) ( )i t s t

( ) ( )j t j te e

2L 2( )d t

22 ( ) ( )( ) 2 Re ( ) IF j jj t t tL d t L d t e e e

*( ) ( )2Re ( ) IFjj t jt teL d t e e PN canceled out!

Self Coherent - Summary

• Spectral efficiency of Coherent Detection• Allows for Linear equalization (CD, PMD

mitigation)• Laser coherency (Linewidth) does not effect Rx

performance→ Low quality laser may be used• Simple Tx & Rx

15

Up-Stream: Reflective Modulation forLaserless Optical Network Unit (ONU)

16

DS Self Coh. Rx

US Tx

ONU

US Carriersource

3 dB coupler

US Tx

Self Coh. Tx

US Rx

Uni-directional Reflective Modulation

17

c W 2c W 3c W c

P

W 2W 3W0

Ue

U

c W 2c W 3c W c

Reflective TxtoRx

I-Q MZM

PBSXy

900

pol rot( )Iu t

( )Qu t

USDS

Bi-directional Reflective Modulation

18

W 2W 3W0

Ue

DP

c W 2c W 3c W c

U UxD

c W 2c W 3c W c

D+RBSP+RBS

c W 2c W 3c W cReflective Tx

toRx

I-Q MZM

PBSXy

900

pol rot( )Iu t

( )Qu t

USDS

Bi-directional Reflective Modulation

19

W 2W 3W0

Ue

DP

c W 2c W 3c W c 4c W

OpticalSSB

Reflective TxtoRx

I-Q MZM

PBSXy

900

pol rot( )Iu t

( )Qu t

USDS U UxD

c W 2c W 3c W c 4c W

c W 2c W 3c W c 4c W

URBS UxDRBS

Pslot

Uslot

Dslot

Gslot

PUDG pattern

OTONES network

• A new bi-directional access network designed from the ground up at the system, sub-system and component levels– low-cost– power-efficient– long-reach– spectral-efficiency

• Applying Self-coherent det. & reflective modulation• 1 Gbps (peak) per user, low rate ADC (<500 MSamp/s)• Total Throughput:

– Class I: 10G/10G over 12.5 GHz – 40 dB reach - lowest-cost– Class II: 20G/20G over 25 GHz – 38.5 dB reach - mid-cost– Class III: 40G/40G over 50 GHz – 35 dB reach - highest cost

20

Remote HU

BRem

ote HUB1 N

1:64Passivesplitter

(De)IL(De)IL

WDMWDM

RemoteNODES

ONU64

ONU2

ONU1

ONU64

ONU2

ONU1

OLT

Feederfiber

DS

US

DS Tx-s

US Rx-s

21N

21N

ODN

12.GHz-off-grid WDM

ODN

@OLT: US Symbol SNR=18.5 dB

@ONUDS Symbol

SNR=18.5 dB

/

8DSPdBm

11 (37 )dB Km

(min Symbol SNR for 16QAM=16.5 dB)

↓(a)↑(e)

↓(b)

1 2

↑(c)

WDM

WDM

EDFAs+Circulators

US OSNR@ Photo-Diode=19 dB

DS OSNR = 17.1 dB

Pslot

Uslot

Dslot

Gslot

Pslot

Uslot

Dslot

Gslot

@ O

LT

@ H

UB

f

25 GHz DS OFDM SPECTRUM

DS

DS

(a)

(b)

seed

seed

SPECTRAL DESIGN

SLICE 2

SLICE 1

ON

U R

x DS optical signal@ONU PD

Plantarchitecture ofOTONESlong-reachPON:

11 dBfeederfiber

optical filtering+OA

Class B+ ODNs:29 dB

Loss budget

11 dB feeder+ 29 dB ODN=40 dB loss budget(Class I)

Backward-compatible w/ existing ODN PON Plantand may even co-exist with (X)GPON, TWDM, etc. 21

OTONES ONU

90 degPOL.ROT.

Si PIC

Y

X-POL(rotatedY-POL)

OTONES ONU

Var.SPLIT

Q I

SOA

X

SMF FIBER IN/OUT

X-POL

DiscreteOpticalComp.

PBS

Y-POLRx

X-POLRxTIA TIA

TRANSCEIVER DSP

SSBMod.

Packet SW.+ User I/F ONUASIC

analogdigital

OF

IQ MODBi-Directional

Postamp.

LPF

Postamp.

LPF

Drvamp

I-ADC Q-ADC I-ADC Q-ADCI-DAC Q-DAC

Drvamp

10nm thin-film OBPF

VGA VGAVar.GainAmp.

PD PD

Data in/out

Signal here contains asingle-slice

A patent app was filed early in 2010

X-POLREMODY-POLREMOD

22

MIXED-SIGNAL ASIC

thin-film optical filteridentical for all ONUs“colorless” ONU !(no tunable or variableparameters filter in ONU)

Laserless reflective ONU !US re-mod of DS lightby coherent 16-QAMidentical on both X,Y polarizations

Pslot

Uslot

Dslot

Gslot

Pslot

Uslot

Dslot

Gslot

@ O

LT

@Re

mot

e- H

UB

ON

U T

x

MO

D=MIXER

@ R

emot

e-HU

B@

OLT

P U D G P U D G

DS

repe

at

f

25 GHz DS OFDM SPECTRUM

Electricalmodulation signal (US OFDM Info)

DS optical signal @ ONU INPUT to IQ US Modulator

Light @ IQ Mod OUT(re-modulated US)

DS

DS

US

US

(a)

(b)

(c)

(d)

(e)

(a)

seed

seed

SPECTRAL DESIGN

SLICE 2

SLICE 1 filter profile

remodulation

US

DS

SLICE 1

SLICE 1 SLICE 2O

NU

Rx DS optical signal

@ONU PD

X

90 degPOL.ROT.

Si PIC

Y

X-POL(rotatedY-POL)

OTONES ONU

Var.SPLIT

Q I

SOA

X

SMF FIBER IN/OUT

X-POL

DiscreteOpticalComp.

PBS

Y-POLRx

X-POLRxTIA TIA

TRANSCEIVER DSP

SSBMod.

Packet SW.+ User I/F ONUASIC

analogdigital

OF

IQ MODBi-Directional

Postamp.

LPF

Postamp.

LPF

Drvamp

I-ADC Q-ADC I-ADC Q-ADCI-DAC Q-DAC

Drvamp

10nm thin-film OBPF, identical for all ONUs

(practically “colorless”)

VGA VGAVar.GainAmp.

PD PD

Data in/out

Signal here contains asingle-slice

23

ADC/DAC: 156 MHz 417MS/s

narrowband filter anddetect just one stream

ENERGY EFFICIENT

MIXED-SIGNALONU ASIC

Spectral Design

elD U

eln nnD U

elP U

P U

P D

elU

U

DSDET

OTONES simulation resultsDS @ OLT output

DS @Remote Hub output, RHS slice filtered down

ONU PD output, electrical

P DD D

P P2P D

US @ OLT input

eln nnD U

desiredremodspurious

ONU DS 16-QAM constellation after max-ratio polarization-diversity combining

SNR=18.5 dB

OLT US16-QAM constellation after max-ratio polarization-diversity combining

SNR=18.5 dB

24

Ideal 16-QAM SNR=16.5 dB at BER=10-3 2 dB margin

• Bi-directional Network simulation using a Matlab-Simulink Model were performed at the Technion

• ONU Photonic Integrated Circuit (PIC) – Developed at Karlsruhe Institute of Technology (KIT), Germany, Expected May-’14

• ONU Digital Rx implemented at Technion-IIT, on a Xilinx Virtex-6 chip

• OLT Digital Rx, Optical SSB modulator – Implemented at Technion-IIT, expected during Apr-’14

• Proof of concept experiments – planned during Q2 ‘14

OTONES Network Prototype is currently under implementation

25PIC mask – courtesy of Philipp Schindler, KIT, Germany

Conclusions

• Self Coherent Detection – Cost effective scheme for spectral efficient low cost optical links

• Reflective Modulation – Cost effective scheme for bi-directional transmission in access networks

• Both techniques may be applied in future optical access networks (FTTH)

26

that’s it

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