Electronic Dispersion Compensation Electronic Dispersion Compensation for optical communication systemsfor optical communication systems

NEC Labs AmericaNEC Labs America

July 12July 12thth, 2006, 2006

Techniques for EDCTechniques for EDC

FFE/DFEFFE/DFE Single Side Band (SSB) with MicrostripeSingle Side Band (SSB) with Microstripe MLSEMLSE Volterra SeriesVolterra Series Pre-distortion (including line-coding)Pre-distortion (including line-coding) HybridsHybrids

FFE and DFEFFE and DFE

Standard techniques for equalization of linear Standard techniques for equalization of linear channelschannels

Easiest to implement, but worst performance Easiest to implement, but worst performance compared to other techniques in linear systemscompared to other techniques in linear systems

Performance further degraded with nonlinear Performance further degraded with nonlinear systems such as the optical channelsystems such as the optical channel

DLDL(ps/nm)(ps/nm) OSNROSNR(dB)(dB) CriterionCriterion AuthorAuthor RemarksRemarks

22402240 22.722.7 BER=1e-9BER=1e-9 Watts Watts (UCL)(UCL)

NRZ, 5-tap FFE + 2-NRZ, 5-tap FFE + 2-stage DFE, optimized stage DFE, optimized for min. BERfor min. BER

Experiments:

SSB transmissionSSB transmission

SSB preserves phase information, making SSB preserves phase information, making the whole system linearthe whole system linear

Compensation achieved by using Compensation achieved by using Microstrip linesMicrostrip lines

DLDL(ps/nm)(ps/nm) OSNROSNR(dB)(dB) CriterionCriterion AuthorAuthor RemarksRemarks

20402040 (High)?(High)? BER=1e-10BER=1e-10 Watts Watts (UCL)(UCL)

NRZ, Optical filter to NRZ, Optical filter to generate SSBgenerate SSB

54405440 (High)? (High)? BER=1e-9BER=1e-9 SiebenSieben

(TRLabs, (TRLabs, Canada)Canada)

NRZ, MZ Modulator NRZ, MZ Modulator to generate SSBto generate SSB

Experiments:

MLSEMLSE Theoretically optimal detector (with infinite states and Theoretically optimal detector (with infinite states and

continuous sampling). Practically, 2 Sa/b is good continuous sampling). Practically, 2 Sa/b is good enough. Memory depends on amount of Dispersionenough. Memory depends on amount of Dispersion

Need correct noise statistics, but usually use Gaussian Need correct noise statistics, but usually use Gaussian approximationapproximation

DLDL(ps/nm)(ps/nm) OSNROSNR(dB)(dB) CriterionCriterion AuthorAuthor RemarksRemarks35703570 1414 BER=1e-3BER=1e-3 Napoli (Italy)Napoli (Italy) NRZ, 2 Sa/b, NRZ, 2 Sa/b,

Memory=4, Gaussian Memory=4, Gaussian noise stat.noise stat.

35003500 1313 BER=3e-4BER=3e-4 Elbers Elbers (CoreOptics)(CoreOptics)

ODB, 2 Sa/b, ODB, 2 Sa/b, Memory=2, ? Noise Memory=2, ? Noise stat.stat.

30003000 1818 BER=1e-3BER=1e-3 Farbert Farbert (CoreOptics(CoreOptics

NRZ, 2 Sa/b, NRZ, 2 Sa/b, Memory=2, ? Noise Memory=2, ? Noise stat.stat.

Experiments:

Volterra SeriesVolterra Series

Taylor series approximation of nonlinear Taylor series approximation of nonlinear systems with memorysystems with memory

FFE/DFE with taps that are coefficients of FFE/DFE with taps that are coefficients of nonlinear terms nonlinear terms

Performance close to MLSE, but hard to Performance close to MLSE, but hard to optimize tap coefficientsoptimize tap coefficients

DLDL(ps/nm)(ps/nm) OSNROSNR(dB(dB))

CriterionCriterion AuthorAuthor RemarksRemarks

45904590 1313 BER=1e-3BER=1e-3 Xia (Kiel, Xia (Kiel, Germany)Germany)

ODB, 4-tap FFE + 1-ODB, 4-tap FFE + 1-stage DFE+ 2stage DFE+ 2ndnd order order nonlinear terms, tap nonlinear terms, tap weights optimized for weights optimized for MMSEMMSE

Experiments:

Pre-distortion (1): Pulse ShapingPre-distortion (1): Pulse Shaping Modulation formats such as duobinary are line coding Modulation formats such as duobinary are line coding

techniques that can be thought of as a kind of Pre-distortiontechniques that can be thought of as a kind of Pre-distortion

DLDL(ps/nm)(ps/nm) CriterionCriterion AuthorAuthor33153315 BER=1e-10BER=1e-10 Price (Alcatel)Price (Alcatel)

35003500 BER=1e-10BER=1e-10 Kuwano ( NTT Japan)Kuwano ( NTT Japan)

33663366 BER=1e-10BER=1e-10 Pierre (Alcatel)Pierre (Alcatel) Note: Dispersion values correspond to no power penalty compared to back-to-backNote: Dispersion values correspond to no power penalty compared to back-to-back

All Duobinary simulations/experiments show optimal system performance at All Duobinary simulations/experiments show optimal system performance at certain values of dispersion, probably because duobinary spectrum partially certain values of dispersion, probably because duobinary spectrum partially cancel the dispersion effectcancel the dispersion effect

Simulations show more complicated line coding further enhance dispersion Simulations show more complicated line coding further enhance dispersion tolerance (Forestieri & Prati, JLT Nov. 2001) tolerance (Forestieri & Prati, JLT Nov. 2001)

Experiments:

Predistortion (2): Inverting the Predistortion (2): Inverting the dispersive Channeldispersive Channel

EDC at transmitter to exactly cancel the channel effects (analogous EDC at transmitter to exactly cancel the channel effects (analogous to Pre-chirping). The non-linearity of photo-detector becomes a non-to Pre-chirping). The non-linearity of photo-detector becomes a non-issueissue

Requires knowledge of the channel. Not a problem for CD since its Requires knowledge of the channel. Not a problem for CD since its relatively static. For PMD, might not be practical since it requires relatively static. For PMD, might not be practical since it requires regular channel feedbackregular channel feedback

DLDL(ps/nm)(ps/nm) OSNROSNR(dB)(dB) CriterionCriterion AuthorAuthor6000060000 1010 BER=1e-3BER=1e-3 McNicol McNicol

(Nortel)(Nortel)

8243382433 10.510.5 BER=3e-3BER=3e-3 McGhan McGhan (Nortel)(Nortel)

Experiments:

Hybrids: Pre-distortion and Hybrids: Pre-distortion and electronic processing at receiverelectronic processing at receiver

Most common form of hybrid investigated is Duobinary modulation Most common form of hybrid investigated is Duobinary modulation with FFE/DFE/MLSE in IM/DD channels. With Duobinary with FFE/DFE/MLSE in IM/DD channels. With Duobinary modulation, FFE/DFE at receiver didn’t help while MLSE still modulation, FFE/DFE at receiver didn’t help while MLSE still provides benefits.provides benefits.

• In coherent systems with nonlinear effects, Savory (UCL, Elec. Lett. In coherent systems with nonlinear effects, Savory (UCL, Elec. Lett. March 2006) showed through simulations that half pre-distortion – March 2006) showed through simulations that half pre-distortion – half receiver EDC optimizes performancehalf receiver EDC optimizes performance

DLDL(ps/nm)(ps/nm) OSNROSNR CriterionCriterion AuthorAuthor RemarksRemarks35003500 1313 BER=3e-4BER=3e-4 Elbers Elbers

(CoreOptics)(CoreOptics)ODB, MLSE with 2 Sa/b, ODB, MLSE with 2 Sa/b, Memory=2, ? Noise stat.Memory=2, ? Noise stat.

43124312 1313 BER=1e-3BER=1e-3 Gnauck (Bell Gnauck (Bell Labs)Labs)

ODB, MLSE with 2 Sa/b, ODB, MLSE with 2 Sa/b, Memory=2, ? Noise stat.Memory=2, ? Noise stat.

Experiments: