Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
Crosstalk suppression in an all-optical Crosstalk suppression in an all-optical symmetric Mach-Zehnder (SMZ) symmetric Mach-Zehnder (SMZ)
switch employing un-equal control switch employing un-equal control pulsespulses
Hoa Le Minh, Fary Z Ghassemlooy and Wai Pang Ng
Optical Communications Research GroupNorthumbria Communications Research Lab
Northumbria University, U.K.
International Symposium on Telecommunications, Sep. 10-12, 2005, Shiraz, Iran
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
ContentsContents
• Introduction
• All-optical Switches
• Symmetric Mach Zehnder Switch (SMZ)
• Simulation Results
• Conclusions
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
IntroductionIntroduction
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 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
All-optical Switches contd.
I- Nonlinear Optical Loop Mirror (NOLM)
CP
50:50
CW CCW
Input port Output port
Reflected portData 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
2cos1 2 tTx
• If = , then Tx (t) = 1 (i.e.100%
transmittance in port 2)
Transmission is:
• Polarisation • Long walk-off time
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
All-optical Switches contd.
II- Terahertz Optical Asymmetric Demultiplexer (TOAD)
CP
SOA
50:50
CW CCW
Input port Output port
Reflected port
Shortfibreloop
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
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ SwitchSMZ 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
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ Switch – SMZ Switch – With ControlWith Control
0)()0(1, LAout
UAoutout EEE
)2/()2/(2, LAout
UAoutout EEE
No control pulse is applied
)()(1, LAout
UAoutout EEE
0)2/()2/3(2, LAout
UAoutout EEE
Control pulses (CP1 & CP2) are applied
)2/(LAoutE
C2
Input signal
SOA1
SOA2
Port 1
C3 C4 C1
OFDL-1
OFDL-2
Port 2
)()(1, LAout
UAoutout EEE
Tdelay
)0(1UAE
)2/(2 LAE
)0(,2UA
inE
)2/(,1LA
inE
)(UAoutE
)2/()2/3(2, LAout
UAoutout EEE
Tdelay
CP1
CP2
PBS – Polarization beam splitter OFDL– Optical fibre delay line
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ – SMZ – Switching WindowSwitching Window
Switching window profile at output port 1
)cos()()(2)()()(8
1)( 21211, tGtGtGtGtPtP inout
)cos()()(2)()()(8
1)( 21212, tGtGtGtGtPtP inout
))(cos(.)()(2)()(25.0)( 21211 ttGtGtGtGtW ))(cos(.)()(2)()(25.0)( 21211 ttGtGtGtGtW
21 /ln5.0 GGLEF (LEF: SOA linewidth enhancement factor)
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ - SMZ - Switching WindowSwitching Window
40 45 50 55 60 65 70 750
5
10
15
20
25SMZ switching window
Time (ps)
SM
Z g
ain
40 45 50 55 60 65 70 750
5
10
15
20
25SMZ switching window
Time (ps)
SM
Z g
ain
CP1=CP2CP1=CP2
Recovery region
• 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
SMZ – SMZ – With Unequal Control With Unequal Control PowerPower
CP1 > CP2CP1 > CP2
• Make CP2 < CP1 to minimize the recovery gain difference.• Reduction ratio: R(dB) = CP1(dB) – CP2(dB)
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ - SMZ - Simulation ModelSimulation Model
Optical receiver
Data pulse train
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ - SMZ - Simulation ParametersSimulation Parameters
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMA - SMA - Simulation ResultsSimulation Results
Inter-channel crosstalk
channelsundesired
channeldesireddB P
PCXT 10log10
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ - SMZ - Simulation ResultsSimulation Results CP1 = CP1 = CP2CP2
Data at output port 1
Eye diagram (@ BER 10-9)
Crosstalk
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMA - Simulation Results SMA - Simulation Results CP2 < CP2 < CP1CP1
• R = 0.6 dB, • Reduced interchannel crosstalk • Improved eye opening, improved bit error rate
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
SMZ – SMZ – BER Simulation ResultsBER Simulation Results
–35.5 dBm–35.5 dBm
R = 0 dB
–37.2 dBm–37.2 dBm
R = 0.6 dB
Prof. Z. Ghassemlooy, IST2005, Shiraz, Iran
ConclusionsConclusions
• 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.Thank you.
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