CHARACTERISATION OF CHARACTERISATION OF A NOVEL DUAL-CONTROL TOAD SWITCHA NOVEL DUAL-CONTROL TOAD SWITCH

H Le-Minh, Z Ghassemlooy, and W P NgH Le-Minh, Z Ghassemlooy, and W P Ng

Optical Communications Research GroupOptical Communications Research GroupSchool of Informatics, Engineering & TechnologySchool of Informatics, Engineering & Technology

Northumbria University, Newcastle, UKNorthumbria University, Newcastle, UK

Lancaster, 30/03 – 01/04/2005

OutlinesOutlines

IntroductionIntroduction

All-optical switchesAll-optical switches

TOAD switch: single & dual controlTOAD switch: single & dual control

Numerical modeling of SOANumerical modeling of SOA

Simulation ResultsSimulation Results

ConclusionsConclusions

IntroductionIntroduction

To enhance high-capacity optical networkTo enhance high-capacity optical network

– Multiplexing: DWDM and OTDMMultiplexing: DWDM and OTDM» Higher channel capacity (higher aggregate bit rate)Higher channel capacity (higher aggregate bit rate)

– All optical switching: All optical switching: » Optical transparency: removing O-E-O conversionsOptical transparency: removing O-E-O conversions

Need an ultra-fast all-optical switches

All-Optical SwitchesAll-Optical Switches

Are based on:Are based on:

Nonlinear effect + optical interferometerNonlinear effect + optical interferometer

Configurations:Configurations:» Nonlinear Optical Loop Mirror (NOLM)Nonlinear Optical Loop Mirror (NOLM)

» Terahertz Optical Asymmetric Demultiplexer (TOAD)Terahertz Optical Asymmetric Demultiplexer (TOAD)

» Symmetric Mach-Zehnder (SMZ)Symmetric Mach-Zehnder (SMZ)

» Ultrafast Nonlinear Interferometer (UNI)Ultrafast Nonlinear Interferometer (UNI)

TOAD SwitchTOAD Switch

• Short fibre loop as the optical interferometer: by the CW & CCW data components

Input Data

Reflected D

ata

CW CCW

SOA

a0o 0.707a0o

0.707a90o

Tasym

TOAD switchTOAD switch

• Short fibre loop as the optical interferometer: by the CW & CCW data components

• Semiconductor Optical Amplifier (SOA) induces nonlinearity

ttGtGtGtGtG CCWCWCCWCWTOAD cos24

1

tG

tGt

CW

CCWln2

Input Data

Transmitted Data

CW CCW

SOA

Control pulse (CP) saturates SOA

Switching window width is defined by the Tasym

TOAD switchTOAD switch

• Short fibre loop (1 m) used as the optical interferometer: by the CW & CCW data components

• Semiconductor Optical Amplifier (SOA): induces nonlinearity

Advantages

• Possible to integrate in chip

• Low control pulse (CP) energy

Disadvantages

• Asymmetric switching window

1. High inter-channel crosstalk

2. Distorted signal pulse shape

Input Data Control pulse (CP)

Transmitted Data

CW CCW

SOA

Output

(Transmitted)

Input Switched

TOAD: Asymmetric Switching WindowTOAD: Asymmetric Switching Window

CP

4 3 2 1

1 2 3 4

CW direction

CCW direction

0 x LSOA

LSOA – x

Single CP

1

CW directionNo effected by CP ( fully amplified after exiting SOA

Follows CP ( experience full saturation effect after exiting SOA

Same as pulse (3) if TSOA_recovery >> TSOA

CCW direction

2

3

4

1

This pulse meets CP at x/2 ( experienced saturation effects of SOA segments up to x/2

2Experienced more partial saturation effect than pulse (1)

3Experienced more partial saturation effect than pulses (1), (2)

4

Any pulse following pulse (4) will experience the full saturation effect until SOA carrier density recovers

TOAD: Asymmetric Switching Window –TOAD: Asymmetric Switching Window –contd.contd.

1

CW directionNo effected by CP ( fully amplified after exiting SOA

Follows CP ( experience full saturation effect after exiting SOA

Same as pulse (3) if TSOA_recovery >> TSOA

CCW direction

2

3

4

1

This pulse meets CP at x/2 ( experienced saturation effects of SOA segments up to x/2

2Experienced more partial saturation effect than pulse (1)

3Experienced more partial saturation effect than pulses (1), (2)

4

Any pulse following pulse (4) will experience the full saturation effect until SOA carrier density recovers

Reason: Difference of CW and CCW gain profiles

and not steep

CP

4 3 2 1

1 2 3 4

CW direction

CCW direction

0 x LSOA

LSOA – x

Single CP

GCW(t)

GCCW(t)

Gain

Time

Tasym

SW

TOAD: Symmetric Switching WindowTOAD: Symmetric Switching Window

• Cascading two TOAD switches (Prucnal’02)

• Using dual-control in single TOAD switch

SW1SW2

Input Data

CP CCW

Transmitted Data

CW CCW

SOA

CP

CW

• CPCW and CPCCW are identical

• CPCW and CPCCW are simultaneously applied to the SOA

Therefore, CW and CCW data components will experience the same amplification & saturation effects

(GCW(t) and GCCW(t) are the same but delayed

TOAD: Symmetric Switching Window with Dual TOAD: Symmetric Switching Window with Dual Control PulsesControl Pulses

CW direction

1Pulses before (1) do not meet CPCCW ( experience full amplification

2 Partial saturation by CPCCW

3 More partial saturation by CPCCW

4

If x<LSOA/2, affected by CPCW

( saturated by segments up to LSOA/2

If x>LSOA/2, segments from LSOA/2 to LSOA are further saturated by CPCW and CPCCW

5Pulses after (5) experience full double saturation of SOA when all CPs exit

CCW direction

CPCW

4 3 2

1 3 4 5

CW direction

CCW direction

0 LSOA

1.5LSOA

Dual-CP

CPCCW

1

x LSOA – x

LSOA + x

- x

5

- LSOA/2

2

The effects on CCW data pulses are exactly same as in CW direction!

TOAD: Symmetric Switching Window with Dual TOAD: Symmetric Switching Window with Dual Control PulsesControl Pulses

CW direction

1Pulses before (1) do not meet CPCCW ( experience full amplification

2 Partial saturation by CPCCW

3 More partial saturation by CPCCW

4

If x<LSOA/2, affected by CPCW

( saturated by segments up to LSOA/2

If x>LSOA/2, segments from LSOA/2 to LSOA are further saturated by CPCW and CPCCW

5Pulses after (5) experience full double saturation of SOA when all CPs exit

CCW direction

The effects on CCW data pulses are exactly the same as in CW direction!

CPCW

4 3 2

1 3 4 5

CW direction

CCW direction

0 LSOA

1.5LSOA

Dual-CP

CPCCW

1

x LSOA – x

LSOA + x

- x

5

- LSOA/2

2

Gain

GCW(t)

GCCW(t)Time

SWTasym

Modeling of SOAModeling of SOA

( )( ) ( )( ) ( )

( ) ( ) ( )

11

1

, ,,,

, , ,

m T tot mmem

SOA e SOA p

m m m

g N k t N P k tN k tIN k t t

qV A E

N k t N k t N k t

t--

-

é ùG -ê úD = - - Dê ú

ê úê úë û

= +D

k

k - 1 k +

1

( ) ( ) ( )( )( ) ( ) ( )( )

( ) ( ) ( )

1 1

1 1

, 1, exp 1,

, 1, exp 1,

, , ,

cw m cw m m T

ccw m ccw m m T

tot m cw m ccw m

P k t P k t g N k t N L

P k t P k t g N k t N L

P k t P k t P k t

- -

- -

é ù= - G - - Dê úë û

é ù= + G + - Dê úë û

= +

1. SOA is divided into a number of small segments

2. At each segment, e.g. kth, the arriving powers are from CW & CCW directions

3. The carrier density at each segment is consequently updated by

Simulation Results ISimulation Results I

Dual control: create the steep transitions in the temporal gain profiles ( help to create the steep switching window edges

Gain profiles and switching windows

Simulation Results IISimulation Results II

Carrier density in SOA when single control pulse going through

Time angle

Simulation Results IIISimulation Results III

SOA carrier density with both control pulses propagating within the SOA

Time angle

Single control

Simulation Results IVSimulation Results IV

Dual control: induce less inter-channel crosstalk and less pulse-shape distortion of switched pulse

ConclusionsConclusions

Using dual-control pulses in a TOAD Using dual-control pulses in a TOAD configuration symmetric switching window configuration symmetric switching window profile is obtainedprofile is obtained

Inter-channel crosstalk and distortion of Inter-channel crosstalk and distortion of switched pulse are reducedswitched pulse are reduced

Thank you.Thank you.

Question please?Question please?