CHARACTERISATION OF A NOVEL DUAL-CONTROL TOAD SWITCH H Le-Minh, Z Ghassemlooy, and W P Ng Optical Communications Research Group School of Informatics, Engineering & Technology Northumbria University, Newcastle, UK Lancaster, 30/03 – 01/04/2005

Outlines Introduction Introduction All-optical switches All-optical switches TOAD switch: single & dual control TOAD switch: single & dual control Numerical modeling of SOA Numerical modeling of SOA Simulation Results Simulation Results Conclusions Conclusions

Introduction To enhance high-capacity optical network To enhance high-capacity optical network –Multiplexing: DWDM and OTDM »Higher channel capacity (higher aggregate bit rate) –All optical switching: »Optical transparency: removing O-E-O conversions Need an ultra-fast all-optical switches

All-Optical Switches Are based on: Are based on: Nonlinear effect + optical interferometer Configurations: Configurations: »Nonlinear Optical Loop Mirror (NOLM) »Terahertz Optical Asymmetric Demultiplexer (TOAD) »Symmetric Mach-Zehnder (SMZ) »Ultrafast Nonlinear Interferometer (UNI)

TOAD Switch Short fibre loop as the optical interferometer: by the CW & CCW data components Input Data Reflected Data CWCCW SOA a0oa0o 0.707a  0 o 0.707a  90 o

T asym TOAD switch Short fibre loop as the optical interferometer: by the CW & CCW data components Semiconductor Optical Amplifier (SOA) induces nonlinearity Input Data Transmitted Data CWCCW SOA Control pulse (CP) saturates SOA Switching window width is defined by the T asym

TOAD 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 CWCCW SOA Output (Transmitted) InputSwitched

TOAD: Asymmetric Switching Window CP CW direction CCW direction 0 x L SOA L SOA – x Single CP 1 CW direction No effected by CP ( fully amplified after exiting SOA Follows CP ( experience full saturation effect after exiting SOA Same as pulse (3) if T SOA_recovery >> T SOA CCW direction 2341 This pulse meets CP at x/2 ( experienced saturation effects of SOA segments up to x/2 2 Experienced more partial saturation effect than pulse (1) 3 Experienced 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 – contd. 1 CW direction No effected by CP ( fully amplified after exiting SOA Follows CP ( experience full saturation effect after exiting SOA Same as pulse (3) if T SOA_recovery >> T SOA CCW direction 2341 This pulse meets CP at x/2 ( experienced saturation effects of SOA segments up to x/2 2 Experienced more partial saturation effect than pulse (1) 3 Experienced 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 CW direction CCW direction 0 x L SOA L SOA – x Single CP G CW (t) G CCW (t) Gain Time T asym SW

TOAD: Symmetric Switching Window Cascading two TOAD switches (Prucnal’02) Using dual-control in single TOAD switch SW1SW2 Input Data CP CCW Transmitted Data CWCCW SOA CP CW CP CW and CP CCW are identical CP CW and CP CCW are simultaneously applied to the SOA Therefore, CW and CCW data components will experience the same amplification & saturation effects ( G CW (t) and G CCW (t) are the same but delayed

TOAD: Symmetric Switching Window with Dual Control Pulses CW direction 1 Pulses before (1) do not meet CP CCW ( experience full amplification 2 Partial saturation by CP CCW 3 More partial saturation by CP CCW 4 If x<L SOA /2, affected by CP CW ( saturated by segments up to L SOA /2 If x>L SOA /2, segments from L SOA /2 to L SOA are further saturated by CP CW and CP CCW 5 Pulses after (5) experience full double saturation of SOA when all CPs exit CCW direction CP CW CW direction CCW direction 0L SOA 1.5  L SOA Dual-CP CP CCW 1 x L SOA – x L SOA + x - x- x 5 - L SOA /2 2 The effects on CCW data pulses are exactly same as in CW direction!

TOAD: Symmetric Switching Window with Dual Control Pulses CW direction 1 Pulses before (1) do not meet CP CCW ( experience full amplification 2 Partial saturation by CP CCW 3 More partial saturation by CP CCW 4 If x<L SOA /2, affected by CP CW ( saturated by segments up to L SOA /2 If x>L SOA /2, segments from L SOA /2 to L SOA are further saturated by CP CW and CP CCW 5 Pulses 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! CP CW CW direction CCW direction 0L SOA 1.5  L SOA Dual-CP CP CCW 1 x L SOA – x L SOA + x - x- x 5 - L SOA /2 2 Gain G CW (t) G CCW (t) Time SW T asym

Modeling of SOA k k - 1 k SOA is divided into a number of small segments 2. At each segment, e.g. k th, the arriving powers are from CW & CCW directions 3. The carrier density at each segment is consequently updated by

Simulation 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 II Carrier density in SOA when single control pulse going through Time angle

Simulation Results III SOA carrier density with both control pulses propagating within the SOA Time angle Single control

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

Conclusions Using dual-control pulses in a TOAD configuration symmetric switching window profile is obtained Using dual-control pulses in a TOAD configuration symmetric switching window profile is obtained Inter-channel crosstalk and distortion of switched pulse are reduced Inter-channel crosstalk and distortion of switched pulse are reduced

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