PowerPoint Presentationtcc/NgOFC2007Slides.pdfTitle PowerPoint Presentation Created Date 4/3/2007...

Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links

Using IIR Equalization

George Ng & Anthony Chan CarusoneDept. of Electrical & Computer Engineering

University of TorontoCanada

Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 2

Transmitting Data Over Short Multimode Fiber Links

• Data transmission speed limited by intermodal dispersion

• Intermodal dispersion causes a wide variety of channel responses

• Result: Inter-symbol Interference (ISI) at receiver


Modal Dispersion Mitigation

• Two dispersion compensation methods– Optical– Electrical

• Electrical equalization advantages– Low cost– Adaptive– Robust


Typical Equalizer - FIR

ClocklessLow powerGuaranteed stabilityCannot compensate spectral nullsRestricted to manipulating zerosOnly cancels ISI up to length of equalizer

τ

τ

2

1

0


Typical Equalizer - DFE

Compensates spectral nulls without noise enhancementDifficult to meet timing in feedback path at high speedsDifficult timing recovery


IIR Equalizer

ClocklessManipulate both poles and zerosCancels ISI beyond length of equalizer More noise enhancement than DFEPossibly unstable

τ

τ

2

τ

τ

1

0

2

1


System Simulation

• IIR equalization of a 50 m MMF link at 40 Gb/s

• Comparing the performance of a 3-Tap FIR versus a 3-Tap FF and 2-Tap FB IIR equalizer

• Both equalizers have Ts/2 tap spacing

MMF Fiber Channel

AWGNTransmit

FilterReceive

FilterNRZ Zero AveragePRBS Sequence

Generator

Eye DiagramIIR Equalizer


MMF Fiber Channel Model

• Statistical MMF channel model• Based on restricted launch scheme at

various radial offsets• Model represents the performance of the

worst-case 5% of installed fibers• Model linearly scaled from original 300 m

length to 50 m


IIR Coefficient Optimization

τ

τ

b2

τ

τ

IN OUT

b1

b0

a2

a1

τ

τ

IN OUT

b2

b1

b0

τ

bn

bn-1


Definition: ISI Penalty

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5Eye Diagram

Time (ps)

Am

plitu

deInner Eye Opening An

Outer Eye Opening A0

ISI Penalty = 10*log10(A0/An)


0 25 50 75 100 1250

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Time (ps)

Am

plitu

de

Channel Pulse Response

Example Channel

Unequalized ChannelISI Penalty = 20.3 dBData Dependent (DD) Jitterpp = 21.4 ps

54.8 ps

0 10 20 30 40 50-1

-0.5

0

0.5

1

Time (ps)A

mpl

itude


0 5 10 15 20-1.5

-1

-0.5

0

0.5

1

1.5

2M

agni

tude

Normalized Delay τ = Ts/20 5 10 15 20

-2

-1

0

1

2

Mag

nitu

de

Normalized Delay τ = Ts/2

IIR Equalizer

τ

τ

IN OUT

0.31

-0.98

1.51

3-Tap FIR

Equalizer Performance


Equalizer Performance

3-Tap FIR EqualizedISI Penalty = 3.9 dBDD Jitterpp = 11.4 ps

IIR EqualizedISI Penalty = 1.1 dBDD Jitterpp = 3.3 ps

0 10 20 30 40 50-1.5

-1

-0.5

0

0.5

1

1.5

Time (ps)

Am

plitu

de

0 10 20 30 40 50-1.5

-1

-0.5

0

0.5

1

1.5Eye Diagram

Time (ps)A

mpl

itude


Statistical Analysis – ISI Penalty

0

10

20

30

40

50

60

70

80

0 - 0.5 0.5 - 1.5 1.5 - 2.5 2.5 - 3.5 3.5 - 4.5 4.5 - 5.5 5.5+ISI Penalty [dB]

# Fi

bers

17 um IIR17 um FIR

Total = 108 Fibers


Statistical Analysis - Jitter

Total = 108 Fibers

0

10

20

30

40

50

60

70

0 - 0.5 0.5 - 1.5 1.5 - 2.5 2.5 - 3.5 3.5 - 4.5 4.5 - 5.5 5.5+Data-Dependent Jitterpp [ps]

# Fi

bers

17 um IIR17 um FIR


Conclusion

• Introduced IIR equalizer for intermodal dispersion compensation

• Demonstrated the effectiveness of the IIR equalizer over the FIR equalizer

• Statistical analysis shows that an IIR equalizer equalizes 90% of the 50 m MMF links at 40 Gb/s– < 2.5 dB of ISI penalty for the 5% worst case fibers– < 3.75 ps of data-dependent peak-to-peak jitter


Questions?

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