H. Le-Minh, Z. Ghassemlooy, W.P. Ng. and R. Ngah

Optical Communication Research Group

School of Engineering & Technology

Northumbria University, Newcastle, UK

http://soe.unn.ac.uk/ocr/

TOAD Switch

with Symmetric Switching Window

London Communications Symposium 2004, Sept. 13th – 14th

Outlines

Introduction

All-optical switches

TOAD switch

Simulation Results

Conclusions

Introduction

How to enhance high-capacity optical network?

Introduction

How to enhance high-capacity optical network?

Multiplexing Wavelength Division Multiplexing (WDM) Time Division Multiplexing (TDM)

Introduction

How to enhance high-capacity optical network?

Multiplexing Wavelength Division Multiplexing (WDM) Time Division Multiplexing (TDM)

Removing the O/E/O conversions bottleneck

Introduction

How to enhance high-capacity optical network?

Multiplexing Wavelength Division Multiplexing (WDM) Time Division Multiplexing (TDM)

Removing the O/E/O conversions bottleneck

All optical processing

Introduction

How to enhance high-capacity optical network?

Multiplexing Wavelength Division Multiplexing (WDM) Time Division Multiplexing (TDM)

Removing the O/E/O conversions bottleneck

All optical processing: e.g. OTDM + all-optical switch

All-optical Switches

Mechanism:Exploiting the combination of destructive interferences introduced by nonlinearity element to switch/demultiplex target data

All-optical Switches

Mechanism:Exploiting the combination of destructive interferences introduced by nonlinearity element to switch/demultiplex target data

Configurations: Loop

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) …

All-optical Switches

Mechanism:Exploiting the combination of destructive interferences introduced by nonlinearity element to switch/demultiplex target data

Configurations: Loop

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) …

All-optical Switches: NOLM

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

• Non-integrated capability

• High control pulse (CP) energy

All-optical Switches: TOAD

Terahertz Optical Asymmetric Demultiplexer (TOAD)

CP

SOA

50:50

CW CCW

Input port Output port

Reflected port

Fibreloop

Data in

Reflected data

Switched data

• Introduced by P. Prucnal (1993)

• Only Semiconductor Optical Amplifier (SOA) induces nonlinearity

• Possible to integrate in chip

• Low control pulse (CP) energy

• High inter-channel crosstalk

• Asymmetrical switching window profile

All-optical Switches: TOAD

Terahertz Optical Asymmetric Demultiplexer (TOAD)

CP

SOA

50:50

CW CCW

Input port Output port

Reflected port

Fibreloop

Data in

Reflected data

Switched data

• Introduced by P. Prucnal (1993)

• Only Semiconductor Optical Amplifier (SOA) induces nonlinearity

• Possible to integrate in chip

• Low control pulse (CP) energy

• High inter-channel crosstalk

• Asymmetrical switching window profile

TOAD: Switching Window Profile

It mainly depends on the gains and phase as:

ttGtGtGtGtG CCWCWCCWCWTOAD cos24

1

tG

tGt

CW

CCWln2

• GCW(t) and GCCW(t) are the temporal gain-profiles of CW and CCW data components

• (t) is the temporal phase difference between CW and CCW components

• is the linewidth enhancement factor

TOAD: Single Control Pulse

Effects data CW and CCW components passing through SOACase 1: No CP

SOA

CW

CCW

Data propagating in SOA experience partial-gain amplification

Partly amplified

CP

SOA

50:50

CW CCW

Input port Output port

Reflected port

Fibreloop

Data in

Reflected data

Switched data

TOAD: Single Control Pulse

SOA

CW

CCW

SOA

CW

CCW

Data propagating in SOA experience partial-gain amplification

After passing full-length SOA, data experience full-gain amplification

Partly amplified Fully amplified

Effects data CW and CCW components passing through SOACase 1: No CP

TOAD: Single Control Pulse

Case 2: With CP applied to the SOA in CW direction

SOA

CW

CCW

Partly amplified

Fully amplified

TOAD: Single Control Pulse

SOA

CW

CCW

SOA

CW

CCW

Data will experience full-gain amplification prior to CP being applied

Case 2: With CP applied to the SOA in CW direction

Partly amplified

Fully amplified

Co-propagating saturation (Will experience full saturation when data exits SOA)Counter-propagating saturation (Will not experience full saturation when data exits SOA)

TOAD: Single Control Pulse

SOA

CW

CCW

SOA

CW

CCW

Data will experience full-gain amplification prior to CP being applied

Data seeing saturated part of SOA will experience partial saturation

Case 2: With CP applied to the SOA in CW direction

Partly amplified

Fully amplified

Co-propagating saturation (Will experience full saturation when data exits SOA)Counter-propagating saturation (Will not experience full saturation when data exits SOA)

TOAD: Single Control Pulse

SOA

CW

CCW

SOA

CW

CCW

Data well before entering of CP to SOA will experience full-gain amplification

Data seeing saturated part of SOA will experience partial saturation

More saturation

Case 2: With CP applied to the SOA in CW direction

Partly amplified

Fully amplified

Co-propagating saturation (Will experience full saturation when data exits SOA)Counter-propagating saturation (Will not experience full saturation when data exits SOA)

TOAD: Single Control Pulse

Case 3: CP exited the SOA

SOA

CW

CCW

Fully amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation Part of transitional

period 2TSOA is partly saturated

TOAD: Single Control Pulse

SOA

CW

CCW

Part of transitional period 2TSOA is partly saturated

Full saturation

Case 3: CP exited the SOA

Fully amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

TOAD: Single Control Pulse

SOA

CW

CCW

Different effects on CW & CCW

Different transitional effects on CW & CCW

Case 3: CP exited the SOA

Fully amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

TOAD: Single Control Pulse

SOA

CW

CCW

2TSOA

Case 3: CP exited the SOA

Fully amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

Dependent on the SOA length

TOAD: Single Control Pulse

SOA

CW

CCW

Case 3: CP exited the SOA

2TSOA

TOAD: Single Control Pulse

SOA

CW

CCW

Issues:

Triangle CW & CCW gain-profiles. Thus Asymmetric switching window!

2TSOA

Case 3: CP exited the SOA

TOAD: Dual Control Pulses

Both control pulses simultaneously excite SOA from both directions.

• Lower inter-channel crosstalk

• Symmetrical switching window profile

CP1

SOA

50:50

CW CCW

Input port Output port

Reflected port

Fibre loop

Data in

Reflected data

Switched data

CP2

TOAD: Dual Control Pulses

Case 1: CP1 and CP2 entering SOA

SOA

CW

CCW

CP1

CP2

Partly amplifiedFully amplified

TOAD: Dual Control Pulses

SOA

CW

CCW

CP1

CP2

CCW data counter-propagate with CP1 will receive partial saturation

CCW data co-propagate with CP2 will receive full saturation

Case 1: CP1 and CP2 entering SOA

SOA

CW

CCW

CP1

CP2

Partly amplifiedFully amplified

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

Similar effects on CW

Case 1: CP1 and CP2 entering SOA

SOA

CW

CCW

CP1

CP2

Similar effects on CW & CCW

SOA

CW

CCW

CP1

CP2

Partly amplifiedFully amplified

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

SOA

CW

CCW

CP1

CP2

Case 2: CP1 and CP2 passing each other within the SOA

At the kth segment of the SOA, where CP2 arrives

Fully amplified

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

At the kth segment of the SOA, where CP2 arrives

• CP1 saturates the kth segment and leaves

• The segment-gain begins recovering after CP1 exited

• With the arrival of CP2, the kth segment is forced into saturation

Case 2: CP1 and CP2 passing each other within the SOA

SOA

CW

CCW

CP1

CP2

Fully amplified

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

SOA

CW

CCW

CP1

CP2

Case 2: CP1 and CP2 passing each other within the SOA

SOA

CW

CCW

CP1

CP2

Fully amplified

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

Segment kth may have more gain saturation

Case 2: CP1 and CP2 passing each other within the SOA

SOA

CW

CCW

CP1

CP2

SOA

CW

CCW

CP1

CP2

Fully amplified

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

SOA

CW

CCW

CP1

CP2

Part of TSOA CCW has partial saturation

(A)

CW or CCW gain- profile

Time

(A)

(B)

(C)

G0

(D) GSAT

Case 3: CP1 and CP2 exit the SOA

Fullly amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

Part of TSOA CCW has partial saturation

(A)

CW or CCW gain- profile

Time

(A)

(B)

(C)

G0

(D) GSAT

Case 3: CP1 and CP2 exit the SOA

SOA

CW

CCW

CP1

CP2

Part of TSOA CCW has partial saturation + deeper saturation

(C)

Fullly amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

Part of TSOA CCW has partial saturation

(A)

Part of TSOA CCW has partial saturation + deeper saturation

(C)

Steep transitionalregion (B)

CW or CCW gain- profile

Time

(A)

(B)

(C)

G0

(D) GSAT

Case 3: CP1 and CP2 exit the SOA

SOA

CW

CCW

CP1

CP2

Fullly amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

Steep transitionalregion (B)

CW or CCW gain- profile

Time

(A)

(B)

(C)

G0

(D) GSAT

Case 3: CP1 and CP2 exit the SOA

SOA

CW

CCW

CP1

CP2

Then full saturation

(D)

Part of TSOA CCW has partial saturation + deeper saturation

(C)

Part of TSOA CCW has partial saturation

(A)

Fullly amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

TOAD: Dual Control Pulses

Steep CW & CCW gain-profiles Symmetric switching window

CW & CCW gain- profiles

Time

Case 3: CP1 and CP2 exit the SOA

SOA

CW

CCW

CP1

CP2

Fullly amplifiedFully saturated

Co-propagating saturationCounter-propagating saturation

Simulation Results

Main parameters

Parameters Values

SOA length 500 m

SOA spontaneous lifetime 100 ps

SOA confinement factor 0.3

SOA transparent carrier density 1024 m-3

SOA line-width enhancement 4

SOA active area 3x10-13 m2

SOA differential gain 2x10-20 m2

Number of SOA segments 100

Control pulse width (FWHM) 1 ps

Single control pulse power (PCP) 1 W

Dual control pulse power (PCP1= PCP2)

0.5 W per CP

Asymmetric SOA placement Tasym 2 ps

Simulation Results: Switching window

Improved switching window by using dual control pulses

Gain profiles and corresponding TOAD switching window

Simulation Results: Multiple Switching Windows

Dual control pulses Constant CP power Variable Tasym

TSOA = 6ps

Need optimum power of CPs for each switching interval

Simulation Results: Imperfect dual controls

Different power ratio of CP2/CP1

Tasym = 2ps

Impairment of CP1’s and CP2’s power Asymmetric switching window

Simulation Results: Imperfect dual controls

Impairment of CP1’s and CP2’s arrivals

Severely bad switching window profiles

CP2 arrives late in comparison with CP1

Tasym = 2ps TSOA = 6ps

Conclusions: TOAD with dual controls

Achieved narrow and symmetric switching window, which will result in reduced crosstalk.

The switching window is independent of the SOA length, and only depends on the SOA offset

Promising all-optical switch for future ultra-fast photonic networks

Acknowledgments

The authors would like to thank the Northumbria University for sponsoring this research

Thanks also for my supervisor team for guiding the research and contributing helpful discussions

Thank you

Thank you!

References

[1] J. P. Sokoloff, P. R. Prucnal, I. Glesk, and M. Kane, “A Terahertz optical asymmetric demultiplexer (TOAD)”, IEEE Photon. Technol. Lett., 5 (7), pp.787-790, 1993

[2] M. Eiselt, W. Pieper, and H. G. Weber, ”SLALOM: Semiconductor Laser Amplifier in a Loop Mirror”, IEEE J. Light. Tech. 13 (10), pp. 2099-2112, 1995

[3] G. Swift, Z. Ghassemlooy, A. K. Ray, and J. R. Travis, “Modelling of semiconductor laser amplifier for the terahertz optical asymmetric demultiplexer”, IEE Proc. Circ. Devi. Syst. 145 (2), pp. 61-65, 1998