Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization George Ng & Anthony Chan Carusone Dept. of Electrical & Computer Engineering University of Toronto Canada
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 4-Gb/s Multimode Fiber Links Using IIR Equalization 2
Modal Dispersion Mitigation Two dispersion compensation methods Optical Electrical Electrical equalization advantages Low cost Adaptive Robust Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 3
Typical Equalizer - FIR Clockless Low power Guaranteed stability Cannot compensate spectral nulls Restricted to manipulating zeros Only cancels ISI up to length of equalizer 2 Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 4
Typical Equalizer - DFE Compensates spectral nulls without noise enhancement Difficult to meet timing in feedback path at high speeds Difficult timing recovery Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 5
IIR Equalizer Clockless Manipulate both poles and zeros Cancels ISI beyond length of equalizer More noise enhancement than DFE Possibly unstable 2 2 Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 6
System Simulation IIR equalization of a 5 m MMF link at 4 Gb/s Comparing the performance of a 3-Tap FIR versus a 3-Tap FF and 2-Tap FB IIR equalizer Both equalizers have T s /2 tap spacing MMF Fiber Channel NRZ Zero Average PRBS Sequence Generator Transmit Filter AWGN Receive Filter IIR Equalizer Eye Diagram Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 7
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 3 m length to 5 m Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 8
IIR Coefficient Optimization IN b OUT IN b OUT b b a b 2 b 2 a 2 b n- b n Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 9
Definition: ISI Penalty.5 Eye Diagram Inner Eye Opening A n.5 Amplitude -.5 - Outer Eye Opening A -.5 5 5 2 25 3 35 4 45 5 Time (ps) ISI Penalty = *log (A /A n ) Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization
Example Channel.7 Amplitude.6.5.4.3.2. 54.8 ps 25 5 75 25 Time (ps) Channel Pulse Response Amplitude.5 -.5-2 3 4 5 Time (ps) Unequalized Channel ISI Penalty = 2.3 db Data Dependent (DD) Jitter pp = 2.4 ps Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization
Equalizer Performance Magnitude 2.5.5 -.5 - -.5 5 5 2 Normalized Delay = T s /2 3-Tap FIR Magnitude 2 - -2 5 5 2 Normalized Delay = T s /2 IIR Equalizer IN.5 OUT.3 -.98 Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 2
Equalizer Performance Amplitude.5.5 -.5 - -.5 2 3 4 5 Time (ps) 3-Tap FIR Equalized ISI Penalty = 3.9 db DD Jitter pp =.4 ps Amplitude.5.5 -.5 - Eye Diagram -.5 2 3 4 5 Time (ps) IIR Equalized ISI Penalty =. db DD Jitter pp = 3.3 ps Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 3
Statistical Analysis ISI Penalty # Fibers 8 7 6 5 4 3 7 um IIR 7 um FIR Total = 8 Fibers 2 -.5.5 -.5.5-2.5 2.5-3.5 3.5-4.5 4.5-5.5 5.5+ ISI Penalty [db] Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 4
Statistical Analysis - Jitter 7 6 7 um IIR 7 um FIR # Fibers 5 4 3 Total = 8 Fibers 2 -.5.5 -.5.5-2.5 2.5-3.5 3.5-4.5 4.5-5.5 5.5+ Data-Dependent Jitter pp [ps] Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 5
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 9% of the 5 m MMF links at 4 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 4-Gb/s Multimode Fiber Links Using IIR Equalization 6
Questions? Electronic Dispersion Compensation of 4-Gb/s Multimode Fiber Links Using IIR Equalization 7