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Acknowledgements & Support: EPSRC, Intel Research

Performance of Adaptive Electronic Feedforward Equalisers in Double Sideband and Single Sideband Links. Philip Watts, Robert Killey Optical Networks Group Department of Electronic and Electrical Engineering University College London, UK. http://www.ee.ucl.ac.uk/~ong.

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Acknowledgements & Support: EPSRC, Intel Research

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  1. Performance of Adaptive Electronic Feedforward Equalisers in Double Sideband and Single Sideband Links Philip Watts, Robert Killey Optical Networks Group Department of Electronic and Electrical Engineering University College London, UK http://www.ee.ucl.ac.uk/~ong Acknowledgements & Support: EPSRC, Intel Research

  2. Introduction • Introduction to electronic dispersion compensation • 10Gb/s Simulations of EDC performance in optically amplified links • Conventional NRZ + FFE/DFE • Single Sideband + FFE • Summary and Conclusions

  3. Aim of Electronic Compensation Fixed compensation using optical Dispersion Compensation Module (approx 300x300x20mm) Adaptive compensation for several impairments included on a receiver integrated circuit.

  4. Research Question • What is the longest range obtainable with only electronic compensation?

  5. Electronic Compensation Issues • Electronic front end requires 10 - 40GHz bandwidth • Recent advances allow cost effective, low power consumption circuits • Non-linear optical to electrical conversion process limits performance • Loss of electric field phase and polarisation information

  6. |E|2 amplitude frequency phase frequency Non-linear Detection Signal after fibre transmission described by amplitude, phase and polarisation state of electric field I ∝optical power ∝|E|2

  7. Linearisation Techniques • Heterodyne Coherent Detection • Pre-compensation Schemes • Directly control the electric field at the transmitter • Single Side-band Transmission • Direct generation using dual electrode MZ • Optical filtering

  8. Electronic Compensators • Feed-forward Equaliser (FFE) • Linear equalisation • Decision Feedback Equaliser (DFE) • Non-linear equalisation • Maximum Likelihood Sequence Estimation (MLSE) • The optimum receiver • High complexity and power consumption • Microstrip/Coaxial Cable • Only suitable for single sideband/coherent systems

  9. Simulations • 10Gb/s Simulations with Chromatic dispersion as the only distortion • Conventional NRZ • SSB directly generated using dual electrode Mach Zehnder • SSB using optical filtering • Noise dominated by Signal-ASE beating as in optically amplified links • Performance Criterion: OSNR (0.1nm RBW) required for 10-9 BER

  10. Semi-Analytic Model Chromatic Dispersion Calculate ASE Beat Noise Laser Mach-Zehnder Square-Law Detector Fixed Low-Pass Filter Signal Processing Tap Adjust PBRS 27-1 FFE Calculate Best BER

  11. Input from optical detector x1’σ1 x0’σ0 x2’σ2 T/2 T/2 c1 c2 c0 X X X Output to Clock/Data Recovery + Feed-forward Equaliser (FFE) Also known as FIR, transversal or tapped delay line filter Noise model is valid for receiver bandwidths of 9-11GHz approx

  12. FFE Clock Recovery Input from optical detector Output Decision Circuit d0 + x Decision Feedback Equaliser (DFE) • Removes post-cursor ISI by subtracting a proportion of previous decisions from the signal • Feedback is noise free

  13. Conventional NRZ Results 16dB Extinction Ratio, 9GHz Receiver Filter, 16ps/nm.km fibre dispersion

  14. Experimental Results • Coming soon – experimental results showing performance of FFE and DFE in DSB links using Intel integrated circuits

  15. Single Sideband Optical Generation • Create SSB directly using a dual electrode Mach-Zehnder modulator • Transmission over 320km Standard fibre at 10Gb/s using microstrip compensator Refs: Sieben et al, J.Lightwave Tech, Vol.17, No.10, 1999 Watts et al, Electronics Letters Vol.40, No.15, p958

  16. xVπ [y(t) + ŷ(t)] - 0.25Vπ Laser MZ Modulator SSB xVπ [-y(t) + ŷ(t)] + 0.25Vπ Single Sideband Optical Generation

  17. SSB direct generation With 9-tap FFE Uncompensated

  18. SSB direct generation

  19. SSB direct generation

  20. Laser SSB Sideband Filter MOD Single Sideband Optical Generation • Use directly or indirectly modulated transmitter with sideband filter • Transmission over 225km at 10Gb/s using coaxial cable and SiGe transversal electrical filter Refs: Bulow, Buchali, Nicolas, OFC 2001, WDD34-1 Watts, Mikhailov, Bayvel, Killey, London Comms Symposium 2003

  21. SSB using optical filter ‘Ideal’ Compensation 9-tap FFE

  22. Summary of Results DSB MZ-SSB OF-SSB

  23. Conclusions • Range of Single Span Conventional NRZ links can be extended with EDC • To 140km with 9-tap FFE • To 156km with 9-tap FFE + DFE • SSB and FFE allows ranges up to ≈750km for multiple span links

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