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.