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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 Contents • Introduction • All-optical Switches • Symmetric Mach Zehnder Switch (SMZ) • Simulation Results • Conclusions 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 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran All-optical Switches • Mechanism: Exploiting the destructive interferences introduced by the nonlinearity 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 All-optical Switches contd. I- Nonlinear Optical Loop Mirror (NOLM) Transmission is: Long loop CW CP Tx t 1 cos 2 2 CCW 50:50 Input port Data in Output port Reflected port • If = , then Tx (t) = 1 (i.e.100% transmittance in port 2) Switched data Reflected data • Long fibre loop to induce the nonlinearity (but weak and not easily controllable) • High control pulse (CP) power Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran • Polarisation • Long walk-off time All-optical Switches contd. II- Terahertz Optical Asymmetric Demultiplexer (TOAD) • Introduced by P. Prucnal (1993) • Nonlinearity: Semiconductor Optical SOA Amplifier (SOA) • Low control pulse (CP) power Short fibre loop CW CP • High inter-channel crosstalk • Asymmetrical switching window profile CCW • Synchronisation 50:50 Input port Output port Data in Switched data Reflected port Reflected data Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ Switch • An optical interferometer with two identical arms • Semiconductor Optical Amplifier (SOA) induce nonlinear effect (XPM) on input data signal • Compact, requiring low optical power (i) No control pulses SOA1 OTDM Signal Pulses Output Port 2 3 dBCoupler SOA2 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ Switch – With Control OFDL-1 CP1 E2UA ,in (0) Input signal SOA1 UA LA Eout,1 Eout ( ) Eout ( ) ) UA Eout ( UA E1 (0) C2 Port 1 Tdelay Tdelay C1 C3 LA E2 (/2) C4 LA Eout ( / 2) CP2 Port 2 UA LA Eout,2 Eout (3 / 2) Eout ( / 2) SOA2 E1LA ,in( / 2) OFDL-2 OFDL– Optical fibre delay line PBS – Polarization beam splitter No control pulse is applied Control pulses (CP1 & CP2) are applied UA LA Eout ,1 Eout (0) Eout ( ) 0 UA LA Eout ,1 Eout ( ) Eout ( ) UA LA Eout ,2 Eout ( / 2) Eout ( / 2) UA LA Eout ,2 Eout (3 / 2) Eout ( / 2) 0 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ – Switching Window Switching window profile at output port 1 1 Pin (t ) G1 (t ) G2 (t ) 2 G1 (t ) G2 (t ) cos( ) 8 1 Pout , 2 (t ) Pin (t ) G1 (t ) G2 (t ) 2 G1 (t ) G2 (t ) cos( ) 8 Pout ,1 (t ) 0.5LEF lnG1 / G2 (LEF: SOA linewidth enhancement factor) W1 (t ) 0.25G1 (t ) G2 (t ) 2 G1 (t )G2 (t ). cos( (t )) Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran 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. SMZ switching window 25 20 SMZ gain 15 10 5 0 40 CP1=CP2 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran 45 50 55 60 Time (ps) 65 70 75 SMZ – With Unequal Control Power • Make CP2 < CP1 to minimize the recovery gain difference. • Reduction ratio: R(dB) = CP1(dB) – CP2(dB) CP1 > CP2 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ - Simulation Model Data pulse train Optical receiver Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ - Simulation Parameters Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMA - Simulation Results Inter-channel crosstalk CXTdB 10log10 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Pdesired channel Pundesired channels SMZ - Simulation Results CP1 = CP2 Eye diagram (@ BER 10-9) Crosstalk Data at output port 1 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 Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran SMZ – BER Simulation Results R = 0 dB –35.5 dBm Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran R = 0.6 dB –37.2 dBm 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 Acknowledgments • This research project is sponsored by the Northumbria University, Newcastle upon Tyne, UK Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran Thank you. Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran