Document

Report
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 ) 
  0.5LEF lnG1 / G2 
(LEF: SOA linewidth enhancement factor)

W1 (t )  0.25G1 (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

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