1. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Crosstalk suppression in an all-optical symmetric Mach-Zehnder (SMZ) switch employing un-equal control pulses Hoa Le Minh, Fary Z Ghassemlooy and Wai Pang Ng Optical Communications Research Group Northumbria Communications Research Lab Northumbria University, U.K. International Symposium on Telecommunications, Sep. 10-12, 2005, Shiraz, Iran

2. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Contents Introduction All-optical Switches Symmetric Mach Zehnder Switch (SMZ) Simulation Results Conclusions

3. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Introduction Ultra-high capacity optical network relies on: –Multiplexing: DWDM and OTDM Higher aggregate bit rate –Optical transparency: Removing Opt.-Elec.-Opt. conversions (bottleneck) in routing, demultpelxing and processing tasks The need ultra-fast all-optical switches

4. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran All-optical Switches Mechanism: Exploiting the destructive interferences introduced by the non- linearity element (based on XPM) to switch/demultiplex target data Configurations: –Loop based Nonlinear Optical Loop Mirror (NOLM) Semiconductor Laser Amplifier in a Loop Mirror (SLALOM) Terahertz Optical Asymmetric Demultiplexer (TOAD) –Others Ultrafast Nonlinear Interferometer (UNI) Symmetric Mach-Zehnder (SMZ) …

5. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran All-optical Switches contd. I- Nonlinear Optical Loop Mirror (NOLM) CP 50:50 CWCCW Input portOutput port Reflected port Data in Reflected data Switched data Long loop Long fibre loop to induce the nonlinearity (but weak and not easily controllable) High control pulse (CP) power If  = , then T x (t) = 1 (i.e.100% transmittance in port 2) Transmission is: Polarisation Long walk-off time

6. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran All-optical Switches contd. II- Terahertz Optical Asymmetric Demultiplexer (TOAD) CP SOA 50:50 CWCCW Input portOutput port Reflected port Short fibre loop Data in Reflected data Switched data Introduced by P. Prucnal (1993) Nonlinearity: Semiconductor Optical Amplifier (SOA) Low control pulse (CP) power High inter-channel crosstalk Asymmetrical switching window profile Synchronisation

7. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ Switch An optical interferometer with two identical arms Semiconductor Optical Amplifier (SOA) induce non- linear effect (XPM) on input data signal Compact, requiring low optical power 3 dBCoupler OTDM Signal Pulses SOA1 SOA2 Output Port 2 (i) No control pulses

8. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ Switch – With Control No control pulse is applied Control pulses (CP1 & CP2) are applied

9. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ – Switching Window Switching window profile at output port 1 (  LEF : SOA linewidth enhancement factor)

10. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ - Switching Window CP1=CP2 Recovery region Problem –The switching window W 1 (t) will not completely close due to the difference of G 1 (t) and G 2 (t) in the recovery region. This is due to CP1 = CP2 thus setting both SOAs at the same initial saturation levels.

11. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ – With Unequal Control Power CP1 > CP2 Make CP2 < CP1 to minimize the recovery gain difference. Reduction ratio: R(dB) = CP1(dB) – CP2(dB)

12. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ - Simulation Model Optical receiver Data pulse train

13. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ - Simulation Parameters

14. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMA - Simulation Results Inter-channel crosstalk

15. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ - Simulation Results CP1 = CP2 Data at output port 1 Eye diagram (@ BER 10 -9 ) Crosstalk

16. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMA - Simulation Results CP2 < CP1 R = 0.6 dB, Reduced interchannel crosstalk Improved eye opening,  improved bit error rate

17. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ – BER Simulation Results –35.5 dBm R = 0 dB –37.2 dBm R = 0.6 dB

18. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Conclusions Proposed SMZ switch with unequal control pulse powers with improved recovery gain profile. Simulation model confirmed: –Improved crosstalk characteristic –Improved optical receiver sensitivity up to 1.7 dB at BER = 10 -9 –Reduced total control signal power

19. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Acknowledgments This research project is sponsored by the Northumbria University, Newcastle upon Tyne, UK

20. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Thank you.