Post on 29-Aug-2020
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 3
Modal Dispersion Mitigation
• Two dispersion compensation methods– Optical– Electrical
• Electrical equalization advantages– Low cost– Adaptive– Robust
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 4
Typical Equalizer - FIR
ClocklessLow powerGuaranteed stabilityCannot compensate spectral nullsRestricted to manipulating zerosOnly cancels ISI up to length of equalizer
τ
τ
2
1
0
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 5
Typical Equalizer - DFE
Compensates spectral nulls without noise enhancementDifficult to meet timing in feedback path at high speedsDifficult timing recovery
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 6
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 7
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 8
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 9
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 10
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)
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 11
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 12
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 13
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 14
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 15
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 16
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
Electronic Dispersion Compensation of 40-Gb/s Multimode Fiber Links Using IIR Equalization 17
Questions?