Hoa Le Minh, Fary Z Ghassemlooy and Wai Pang Ng Optical Communications Research Group

1. 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 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

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

3. 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 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

4. 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) • … Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

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

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

7. SOA1 OTDM Signal Pulses Output Port 2 3 dBCoupler SOA2 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 (i) No control pulses Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

8. OFDL - 1 CP1 UA E ( 0 ) UA LA = p + p E E ( ) E ( ) SOA1 2 , in out , 1 out out UA p E ( ) out Input UA E ( 0 ) signal 1 C Port 1 2 T T delay delay C Port 2 3 C C p LA 1 E ( / 2 ) 4 2 LA p E ( / 2 ) = UA p + LA p E E ( 3 / 2 ) E ( / 2 ) out CP2 out , 2 out out SOA2 LA p E ( / 2 ) 1 , in OFDL - 2 PBS – Polarization beam splitter OFDL – Optical fibre delay line Control pulses (CP1 & CP2) are applied No control pulse is applied SMZ Switch – With Control Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

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

10. Recovery region CP1=CP2 SMZ - Switching Window • Problem • The switching window W1(t) will not completely close due to the difference of G1(t) and G2(t) in the recovery region. This is due to CP1 = CP2 thus setting both SOAs at the same initial saturation levels. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

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

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

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

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

15. Crosstalk SMZ - Simulation ResultsCP1 = CP2 Data at output port 1 Eye diagram (@ BER 10-9) Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

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

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

18. 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 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran

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

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