Homodyne Ultra-Dense WDM PONs: Can They be Affordable?

Homodyne Ultra dense WDM-PONs: can they beaffordable in access?

Josep PratJosep M. Fabrega

Ronald Freund

Universitat Politecnica de Catalunya - BarcelonaTechFraunhofer Institute for Telecommunications - Heinrich Hertz Institut

[email protected]

June 10, 2010

J. Prat, J. M. Fabrega, R. Freund (UPC-HHI) Homodyne UD-WDM PONs June 2010 1 / 27

Outline

Introduction

Transceiver architectures

Case studies

Conclusions


Introduction

I Novel multimedia applicationsI Voice over IPI Video on demandI HDTV

I User bit rate demand expected to be increasingI Nielsen law: bandwidth per user increments in a 50 % per yearI In 2020 each user would demand an average bandwidth of 1 Gb/s


FTTH roadmap and tendencies in PONs

Actual tendencies:I PON standardization bodies pushing towards high capacity

systems by increasing the aggregate bit rate (10 Gb/s)I ONU operates at a very high bit rate in the opto-electronics

transceivers just to use a small fraction of it (≈ 3 %)

High power consumption!New philosophy proposed, exploiting the pure WDM dimension


Towards this new philosopy

Advantages DrawbacksIM-DD

I Simplicity I sensitivityI optical filters selectivity

Coherent

I Use of advanced modulation formatsI Electrical filtering for channel selectionI Detection amplitude, phase and polarizationI Linear transformation optical⇒ electricalI Increase of sensitivity

I Image frequency (heterodyne)I Phase noise (Homodyne)


How to minimize this phase error?

I OPLLs: Several architectures proposedI Decision driven [1]I Costas [2]I Balanced [3]I Subcarrier modulated [4]

I Phase diversity with zero IF receiverI Analog mutiple differential detection [5]I Digital phase estimation:

I Wiener filter [6, 7]I Regenerative frequency dividers [8]I Viterbi & Viterbi [9, 10]

But many of them are not the cheap solutions we search for!

New solutions have to be proposed


How to minimize this phase error?

I OPLLs: Several architectures proposedI Decision driven [1]I Costas [2]I Balanced [3]I Subcarrier modulated [4]

I Phase diversity with zero IF receiverI Analog mutiple differential detection [5]I Digital phase estimation:

I Wiener filter [6, 7]I Regenerative frequency dividers [8]I Viterbi & Viterbi [9, 10]

But many of them are not the cheap solutions we search for!New solutions have to be proposed


Lock-In amplified OPLL

I Low-cost PLL based on balanced OPLL [3]

I Compared to other oPLL architectures:I Costas [2]I Balanced [3]

I Subcarrier modulated [4]I 10 ns loop delay (eq. 20 cm of fiber)

Linewidth tolerance BER 10−9 Linewidth tolerance BER 10−3

Balanced 420 kHz 1.2 MHzCostas 1.15 MHz 2.65 MHzSCM 1.35 MHz 2.75 MHz

Lock-In amplified 675 kHz 3.1 MHz

Lock-In amplifier OPLL is a competitive low-cost solution!


Lock-In amplified OPLL

I Low-cost PLL based on balanced OPLL [3]

I Compared to other oPLL architectures:I Costas [2]I Balanced [3]

I Subcarrier modulated [4]I 10 ns loop delay (eq. 20 cm of fiber)

Linewidth tolerance BER 10−9 Linewidth tolerance BER 10−3

Balanced 420 kHz 1.2 MHzCostas 1.15 MHz 2.65 MHzSCM 1.35 MHz 2.75 MHz

Lock-In amplified 675 kHz 3.1 MHz

Lock-In amplifier OPLL is a competitive low-cost solution!J. Prat, J. M. Fabrega, R. Freund (UPC-HHI) Homodyne UD-WDM PONs June 2010 7 / 27

Time switched phase diversity

I Phase diversity by switching from I to Q component at each bitI Less components duplicity than standard phase diversity (lower cost)I 3 dB penalty respect to an ideal system

I Linewidth tolerance for 10−3 BER-floor: 1.8 % of bitrate [11]

I 3 GHz channel spacing for 1 dB penalty at BER of 10−9 [12]I A similar structure has been recently integrated in InP substrate [13]I A more simple structure is achieved when driving the laser directly [14]

Time-switched phase diversity provides high performances at low cost


Outline

Introduction


Case studies

Conclusions


Summary of the performances

Phase noise

Technique Linewidth Penalty Required key Complexitytolerance component

Decision-drive loop 5 MHz 0 dB 90◦ hybrid HighCostas loop 4.9 MHz 0 dB 90◦ hybrid Medium/High

Subcarrier loop 5.1 MHz 0 dB 90◦ hybrid HighBalanced loop 2.4 MHz 2 dB Optical coupler LowLock-In loop 6.4 MHz 1 dB Optical coupler Low

Full phase diversity 5% bitrate 0 dB 90◦ hybrid MediumTime-switch (Scrambler) 1.8% bitrate 4 dB Phase modulator Medium

Time-switch (Direct drive) 3.4% bitrate 4 dB High-chirp laser Low

Penalty is respect to an ideal system whereas tolerance is for a BER-floor of 10−3

Three main approaches: Optical phase locked loop, full phase diversity and time-switched diversity

Polarization mismatch

Local control Polarization diversity Polarization switchingPenalty 0 dB 0 dB 3 dB

Key component Polarization actuator Pol. beam splitter Pol. scrambler/switchResponse time 1 ms – 1 s < 10 µs < 10 µs

Complexity High Med./high Low (if placed at CO)

Several transceiver architectures are going to be discussed in the following slides:I The targeted modulation format is DPSK/BPSK, although other multilevel modulations can be usedI Channel selection is performed by tuning the local laser to the right wavelength and filtered by the electrical filters


Operation specifications

I Bitrate fixed at 1 Gb/s, to directly transmit the common EPONprotocol over fiber

I Downstream modulation format to be used is PSK, because of itsgood trade-off between performances and simplicity

I Upstream modulation formatI PSK preferredI IM can be also used with an asymmetrical up/down data rate to not

to penalize optical power budgetI Digital and analog signal processing adopted against impairmentsI Assume a double fiber network, avoiding Rayleigh backscattering


Transceiver architectures proposedA

B

C

D

E

F

G

H

I

I Architectures A, C, E and G are intended for BPSK modulationI DPSK modulation format has to be used in architectures B, D, F, and II Polarization is managed at OLT for architectures A, B, E, F, G, H and II In transceivers C and D a PBS used for achieving polarization diversity

I For digital approaches (A, C, E, G), Inside digital I and Q post-processing several basic operations are performed:I phase estimationI frequency estimation and controlI data estimation

I polarization switching combinationJ. Prat, J. M. Fabrega, R. Freund (UPC-HHI) Homodyne UD-WDM PONs June 2010 12 / 27

Transceiver comparison

Arch. Phase handling Polarization handling Processing Sens. penalty Linewidth tolerance CostA 90◦ hybrid Switch at CO Digital 3 dB 5 MHz Med./HighB 90◦ hybrid Switch at CO Analog 4 dB 5 MHz Med./HighC 90◦ hybrid PBS Digital 0 dB 5 MHz Very highD 90◦ hybrid PBS Analog 1 dB 5 MHz Very highE Switch (Scr.) Switch at CO Digital 6 dB 1.8 MHz MediumF Switch (Scr.) Switch at CO Analog 7 dB 1.8 MHz MediumG Switch (Dir.) Switch at CO Digital 6 dB 3.4 MHz LowH Switch (Dir.) Switch at CO Analog 7 dB 3.4 MHz LowI OPLL Switch at CO Analog 4 dB 675 kHz Low

I Architecture with 90◦ hybrids a PBS and DSP (C):I No additional penalty with respect to an ideal systemI Achieves high linewidth toleranceI It is costly because it implies the duplication of many components needed

I Its cost can be low if novel fabrication techniques are used [15]

I Direct-drive time-switching (G):I High penalty (6 dB)I High linewidth toleranceI Reduced complexity and cost

I Requires a fully engineered laser capable to be phase modulated

I OPLL approach (I):I Low complexityI Lower linewidth tolerance (675 kHz)I Delay associated to the optical path length

I Local laser should be embedded with the optical reception front-end


Outline

Introduction


Case studies

Conclusions


Case studies

Two cases of future deployment were tested in the laboratory:

I Subband WDM tree PON, featuring wavelength grooming [16]

I Ring-tree ultra-dense WDM-PON, with transparent remote nodes [17]

Both networks are based on the ultra-dense WDM concept, aiming to giveservice to a high number of users (around 1000), at very high speed (1 Gb/s)


Subband WDM tree PON

I 4 GHz channel spacing and 1 Gb/s data rateI 32 channels accommodated in an ITU-T G.694.1

100-GHz D-WDM channelI Serve 40 x 32 = 1280 users⇒ more than 1 Tb/sI 25 km fiber spool simulated the access trunk fiberI Losses at the AWG were measured to be 6.47 dBI 1:32 power splitter, adding 16 dB lossesI Total network losses were measured to be 27.67 dBI 9 dBm optical output power at CO

I −38.7 dBm of sensitivity (BER=10−9)I Power budget calculated to be 47.7 dB


Ring-tree ultra-dense WDM PON

I Totally passive and transparentI Simple and resilient architecture


Experimental evaluation

I Network designed to offer connectivity to 1024 users

I 4-node configuration

I 8 secondary trees with 1:128 splitting factor

I 4 GHz channel spacing

I Three different cases were investigated: RN1, RN2 and RN4


Results and discussion

BER = 10−9 BER = 10−3

RN1 RN2 RN4 RN1 RN2 RN4Sensitivity −43 dBm −41.3 dBm - −49.1 dBm −49.3 dBm −49.1 dBm

Link Losses 39.4 dB 41 dB 44.2 dB 39.4 dB 41 dB 44.2 dBPower Budget 42.9 dB 41.2 dB - 49 dB 49.2 dB 49 dB

I In normal operation (BER = 10−9), the maximum power budget reached is 41.2 dB arriving to RN2I In resilient mode FEC codes are used to overcome the possible fiber cutI Using FEC codes BER = 10−3 is operable and RN4 can be reached, featuring a power budget of 49 dB


Outline

Introduction


Case studies

Conclusions


Conclusions

I The overall goal of this study was to find whether homodynetransceivers are affordable or not for upgrading the currentstandard PONs

I It was found that they are more power and bandwidth efficientI Several transceiver architectures have been proposed and

discussedI Trade-off between performances and cost is difficult to overcomeI Time-switched diversity transceiver has been implemented

I Upgrading of PON architectures has been discussed forimplementing full ultra-dense WDM networks

I Laboratory testbeds have been developed for two network conceptsI The proposed topologies have been demonstrated to be feasible,

achieving transmission of up to 1 Gb/s in links higher than 25 km


Future lines

Some improvements to be achieved, resulting in a step forward:I Compact coherent transceiver

I State of polarization mismatch between local oscillator andreceived signal

I Careful design of the modulation formats to be usedI Full bidirectionality over a single fiber

I Rayleigh backscatteringI Light reflections

I Spectrum managementI Spectral efficiency maximizationI Wavelength monitoring, control and stabilization


Thank you!!Time for questions...


Bibliography I

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[2] S. Norimatsu, K. Iwashita, and K. Sato.Psk optical homodyne detection using external cavity laser diodes in costas loop.IEEE Photonics Technology Letters, 2(5), 1990.

[3] L. G. Kazovsky.Balanced phase-locked loops for optical homodyne receivers: performance analysis, design considerations, and laserlinewidth requirements.IEEE / OSA Journal of Lightwave Technology, 4:182, 1986.

[4] S. Camatel, V. Ferrero, and P. Poggiolini.2-psk homodyne receiver based on a decision driven architecture and a sub-carrier optical pll.In Proceedings of the Conference on Optical Fiber Communication and the National Fiber Optic Engineers Conference,2006 (OFC/NFOEC 2006), Anaheim (CA), March 2006.

[5] Y. H. Cheng, T. Okoshi, and O. Ishida.Performance analysis and experiment of a homodyne receiver insensitive to both polarization and phase fluctuations.IEEE / OSA Journal of Lightwave Technology, 7:368–374, 1989.

[6] M. G. Taylor.Phase estimation methods for optical coherent detection using digital signal processing.IEEE / OSA Journal of Lightwave Technology, 27:901–913, 2009.

[7] M. G. Taylor.Accurate digital phase estimation process for coherent detection using a parallel digital processor.In Proceedings of 31th European Conference on Optical Communications (ECOC 2005), Glasgow (Scotland), September2005.


Bibliography II

[8] R. Noe.Phase noise-tolerant synchronous qpsk/bpsk baseband-type intradyne receiver concept with feedforward carrier recovery.IEEE / OSA Journal of Lightwave Technology, 23(2), 2005.

[9] D. Van den Borne, C. R. S. Fludger, T. Duthel, T. Wuth, E. D. Schmidt, C. Schulien, E. Gottwald, G. D. Khoe, andH. de Waardt.Carrier phase estimation for coherent equalization of 43-gb/s polmuxnrz-dqpsk transmission with 10.7-gb/s nrz neighbours.In Proceedings of 33th European Conference on Optical Communications (ECOC 2007), Berlin (Germany), September2007.

[10] M. Seimetz.Laser linewidth limitations for optical systems with high-order modulation employing feed forward digital carrier phaseestimation.In Proceedings of the Conference on Optical Fiber Communication and the National Fiber Optic Engineers Conference,2008 (OFC/NFOEC 2008), San Diego (CA), March 2008.

[11] J. M. Fabrega and J. Prat.Homodyne receiver prototype with time-switching phase diversity and feedforward analog processing.OSA Optics Letters, 32(5), 2007.

[12] J. M. Fabrega and J. Prat.Experimental investigation of channel crosstalk in a time-switched phase diversity optical homodyne receiver.OSA Optics Letters, 34(4), 2009.

[13] A. Ramaswamy, L. A. Johansson, J. Klamkin, C. Sheldon, H. F. Chou, M. J. Rodwel, L. A. Coldren, and J. E. Bowers.Coherent receiver based on a broadband phase-lock loop.In Proceedings of the Conference on Optical Fiber Communication and the National Fiber Optic Engineers Conference,2007 (OFC/NFOEC 2007), Anaheim (CA), March 2007.

[14] J. M. Fabrega and J. Prat.Simple low-cost homodyne receiver.In Proceedings of 33th European Conference on Optical Communications (ECOC 2007), Berlin (Germany), September2007.


Bibliography III

[15] N. Keil, H. Yao, C. Zawadzki, W. Doldissen, W. Schlaak, M. Mohrle, and D. Schmidt.Polymer as integration platform for low-cost devices in future optical networks.In Proceedings NOC06, Berlin (Germany), July 2006.

[16] C. Bock, J. M. Fabrega, and J. Prat.Ultra-dense wdm pon based on homodyne detection and local oscillator reuse for upstream transmission.In Proceedings of 32th European Conference on Optical Communications (ECOC 2006), Cannes (France), September2006.

[17] J. M. Fabrega and J. Prat.Ultra-dense, transparent and resilient ring-tree access network using coupler-based remote nodes and homodynetransceivers.In Proceedings of International Conference on Transparent Optical Networks ICTON’09, Ponta Delgada (Azores, Portugal),July 2009.


Homodyne Ultra-Dense WDM PONs: Can They be Affordable?

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