Investigation of Control Pulse Power Effects on Alloptical SMZ Switch Performance

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Investigation of Control Pulse Power Effects on
All-optical SMZ Switch Performance

• H. Le Minh, Z. Ghassemlooy and Wai Pang Ng
• Optical Communications Research Group
• Northumbria University, UK
• http//soe.unn.ac.uk/ocr/

5th International Symposium on Communication
Systems, Networks and Digital Signal Processing
(CSNDSP 2006) Patras (Greece), 19th - 21st July
2006
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Contents

• Introduction
• Overviews of All-optical Switches
• Numerical modelling of SMZ with unequal
  control-pulse powers
• SMZ switch
• Residual Crosstalk Issue
• Unequal control-pulse power scheme
• Simulation results
• Summary

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Introduction All-optical network

• Network transparency ? All-optical core router
• Processing, switching and routing in optical
  domain ? high aggregate throughput
• Optical data packet format is preserved
• Low BER (w/o FEC) and low power penalty of
  switching/routing at each router

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All-optical Switching
1?2
Control path
Case I Without control signals (non-switching
mode) a) Packets are switched to
lower output port b) No signals at
the upper output port (i.e. High
switching extinction ratio)
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All-optical Switching (cont.)
1?2
Control path

• Electrical Switching
• Optical packets have to be converted to
  electrical domain
• Electronically switching speed limitation (lt 40
  Gbits/s)
• All-optical Switching
• Packets remain in optical domain (no error
  addition)
• Ultrafast switching/demultiplexing (up to 160
  Gbits/s)

Case II With control signals (switching mode)
a) Packets are switched to upper
output port b) Control signals set
the ON/OFF of the output ports
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All-optical Switching (cont.)

• Ultrafast all-optical switches (gt 80 Gbits/s) are
  based on
• Optical interferometer Nonlinear Element
• Proposed optical switch configurations
• Nonlinear Optical Loop Mirror (NOLM)
• Terahertz Optical Asymmetric Demultiplexer (TOAD)
• Symmetric Mach-Zehnder (SMZ)
• Ultrafast Nonlinear Interferometer (UNI)

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All-optical Switching (cont.)

• Ultrafast all-optical switches (gt 80 Gbits/s) are
  based on
• Optical interferometer Nonlinear Element
• Proposed optical switch configurations
• Nonlinear Optical Loop Mirror (NOLM)
• Terahertz Optical Asymmetric Demultiplexer (TOAD)
• Symmetric Mach-Zehnder (SMZ)
• Ultrafast Nonlinear Interferometer (UNI)

NOLM Closed loop with a long strong nonlinear
fiber loop (km) Complex and
consuming high optical energy
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All-optical Switching (cont.)

• Ultrafast all-optical switches (gt 80 Gbits/s) are
  based on
• Optical interferometer Nonlinear Element
• Proposed optical switch configurations
• Nonlinear Optical Loop Mirror (NOLM)
• Terahertz Optical Asymmetric Demultiplexer (TOAD)
• Symmetric Mach-Zehnder (SMZ)
• Ultrafast Nonlinear Interferometer (UNI)

TOAD Closed loop with a nonlinear semiconductor
optical amplifier (mm) Complex
but consuming less optical energy
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All-optical Switching (cont.)

• Ultrafast all-optical switches (gt 80 Gbits/s) are
  based on
• Optical interferometer Nonlinear Element
• Proposed optical switch configurations
• Nonlinear Optical Loop Mirror (NOLM)
• Terahertz Optical Asymmetric Demultiplexer (TOAD)
• Symmetric Mach-Zehnder (SMZ)
• Ultrafast Nonlinear Interferometer (UNI)

SMZ Short two-waveguide-arms loop with two
identical SOA (mm) Compact
(integration capability) and consuming much less
optical energy
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All-optical Switching (cont.)

• Ultrafast all-optical switches (gt 80 Gbits/s) are
  based on
• Optical interferometer Nonlinear Element
• Proposed optical switch configurations
• Nonlinear Optical Loop Mirror (NOLM)
• Terahertz Optical Asymmetric Demultiplexer (TOAD)
• Symmetric Mach-Zehnder (SMZ)
• Ultrafast Nonlinear Interferometer (UNI)

UNI Long briefinger fibre with a SOA (mm)
Polarization-dependence issue, consuming low
optical energy as SMZ
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All-optical SMZ Switch
Switching mode a) 2?2 (3-dB)
couplers and optical waveguides
form the constructive/destructive
interferometer b) CP1 and CP2 control
the SOA1 and SOA2 nonlinearities
to change the input signal gain/phase ? Switching
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All-optical SMZ Switch (cont.)
Gain profile of the SOA
(1)
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All-optical SMZ Switch (cont.)
Switching window (SW) gain
(2)
SW width Delay interval between two control
pulses TSW
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Residual Crosstalk in SMZ
SOA recovery region
Switching window
SOA gains
Residual gain Owing to the difference of SOA
gains in recovery region, SW(t) is non zero
outside TSW
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Residual Crosstalk in SMZ (cont.)
Residual Crosstalk
(3)

• Pnt the sum of the output signal power of all
  non-target channels
• Pt the output signal power of the target channel

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Unequal Control-pulse power scheme
a) Equal CPs scheme
b) Unequal CPs scheme
Suppress CXT by overlapping G1 and G2 in gain
recovery region ? PCP1 gt PCP2
? Solving these equations
(4)
R power reduction ratio
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Unequal Control-pulse power scheme (cont.)
Finding the optimum R
Solving (4) to obtain the reduction ratio R
between PCP1 and PCP2
Crosstalk is dependent on the injected CP power
(PCP1) and the reduction ratio R SOA
simulation parameters given in Table 1 in Result
Section
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Simulation Parameters
Table 1 Main parameters
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Simulation Results
Case I Demultiplexing 160-to-10 Gbit/s
Demultiplexing with equal CPs
Demultiplexing with unequal CPs
BER and Power penalty are improved 1dB
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Simulation Results (cont.)
Case I Demultiplexing 160-to-10 Gbit/s
Received power penalty vs. different
demultiplexed OTDM channels (at BER 10-9)
Received power penalty vs. the control power of
PCP1 at R 0 dB and at Ropt

• Power penalty variation among demultiplexed
  channels is small
• Improvement of 1 dB achieved by using optimum
  Ropt

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Simulation Results (cont.)
Case II Demultiplexing at high demltiplexing
rate (160-to-80/160-to-40/160-to-20 Gbit/s)
Improvement
Ropt offers significant reduced power penalty at
high demultiplexing rates
Received power penalties vs. different
demultiplexing rates from an OTDM bit stream of
160 Gb/s
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Simulation Results (cont.)
Case III Switching with wide SW (TSW gt one
channel) and short switching interval (Tint)
Non-overlapping gain recovery region
Overlapping gain recovery region
Switching Extinction ratio (r) is much improved
TSW 4 channels
a) Equal CPs scheme
b) Unequal CPs scheme
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Simulation Results (cont.)
Case III Switching with wide SW (TSW gt one
channel) and short switching interval (Tint)
Unequal CPs r is achieved gt 30 dB
Equal CPs r is small (lt 20 dB)
The extinction ratio (r) vs. the switching
interval (Tint) for various switching window
widths (TSW), at Ropt, and with the bit stream of
160 Gbit/s
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Summary

• Unequal control-pulse power scheme
• Suppression the residual crosstalk by setting
  reduction ratio between control pulses
• BER and received power penalty of SMZ-based
  demultiplexer are reduced in 1 dB
• Switching extinction ratio is enhanced by more
  than 10-dB
• The scheme is effective and simple to implement

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Acknowledgement
Northumbria University for supports and
sponsoring this research
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Thank you.