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Photonics in Switching

Photonics in Switching. Switching Element Technologies. Wojciech Kabacinski Poznan University of Technology Wojciech.Kabacinski@et.put.poznan.pl. Optical switching.

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Photonics in Switching

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  1. Photonics in Switching Switching Element Technologies Wojciech Kabacinski Poznan University of Technology Wojciech.Kabacinski@et.put.poznan.pl

  2. Optical switching • Optical switching, called also photonic switching, enables optical signals to be switched directly from inputs to outputs without conversion to electronic form. • Used in • optical cross-connect systems installed in emerging automated switched optical transport networks (AOTN), • switching nodes using packet, burstand ATM switching.

  3. Capacity and switching time requirements Capacity [number of ports] 10 000 Optical BurstSwitching OXC 1 000 Photonic PacketSwitching 100 OADM 10 Protection 1 10 ns 1 ms 1 ms 1 s Switching time

  4. Switching elements - requirements Number of ports 10 000 Liquid crystal 3DMEMS holo-graphic 1 000 100 Electro-optic High-speed3D MEMS Bubble 2DMEMS 2D MEMS 10 1 10 ns 1 ms 1 ms 1 s Switching time

  5. Switch Technologies and Switching Types (1) • To construct optical switching elements two different technologiesare being used: • guided lightwave based switches – they use fibers or waveguides for transmitting and switching lightwaves, • free-space switches – lightwaves.

  6. Switch Technologies and Switching Types (2) • Each category can be further divided into different classes, depending on the physical phenomena used to switch lightwaves between inputs and outputs. • electro-optic switches – they use an electro-optic effect of a material, i.e. changes of the refractive index due to the application of an electric filed, • acousto-optic switches – they use an acousto-optic effect of a material, i.e. changes of the refractive index due to the application of acoustic waves,

  7. Switch Technologies and Switching Types (3) • thermo-optic switches – they use an thermo-optic effect of a material, i.e. changes of the refractive index due to changes of temperature, • MEMS switches – they use micro-electro-mechanical systems to move fibers, micro-mirrors or prisms, • liquid-crystal switches – they use properties of liquid-crystal materials, where the refractive index is determined by molecular alignment controlled by electric fields, • switches based on optical semiconductor amplifiers.

  8. Classification • Free space switches • Electromechanical (MEMS) • mirrors, prisms • Electro-optic • Liquid crystal switches • Waveguide switches • Electromechanical (MEMS) • moving fibers • Electro-optic • Guided-wave switches, Laser-diode switches, SOA • Thermo-optic • bubble switches

  9. Different implementations and capacities of MEMS switches (1) on-off switch 2 × 2 switch

  10. Different implementations and capacities of MEMS switches (2) 1 × N switches with moving fibers, lenses, and mirrors

  11. Different implementations and capacities of MEMS switches (3) N × N switch

  12. MEMS - 12 switch with moving fibers S N N S 40mm Moving fiber N S f 2,5mm f 3mm University of Tokyo and TDK

  13. MEMS - 12 switch with moving fibers Hewlett-Packard

  14. MEMS 3D switches 2D switches

  15. Lucent and Bell Labs Switch Input and output fibers Moving mirrors

  16. MEMS Control Waveguides Movingmirror

  17. MEMS Output 1 Control voltage Input 2 Mirror Input 1 Output 2

  18. Liquid Crystal Switches Control voltage V1 Electrodes Liquid crystal Glass Fibers

  19. Liquid Crystal Switches Control voltage V2 Electrodes Liquid crystal Glass Fibers

  20. Liquid Crystal Switches Control voltage Fibers Liquid crystal Polarization spliter

  21. Liquid Crystal Switches Control voltage Fibers Liquid crystal Polarization spliter

  22. Bubble Switches Waveguide crossover Row withliquid Silicon plate (SiO2) Waveguide H1, H2, H3, H4:microheaters(under the plate)

  23. Bubble Switches

  24. Laser-Diode Switches Laser-diode amplifiers 3 dB OA Input 1 Output 1 OA Output 2 OA Input 2 OA

  25. Guided-Wave Switches The titanium diffused lithium-niobate (Ti:LiNbO3) directional coupler NiLbO3 substrate Electrodes Waveguides d w L Cross state Bar state Output 1 Input 1 Output 1 Input 1 Input 2 Output 2 Input 2 Output 2

  26. Switching Network Characteristics • Losses • Crosstalk • Number of switching elements • Number of waveguide crossovers • Multicasting • Combinatorial properties • strict-sense nonblocking • wide-sense nonblocking • rearrangeable • blocking • Other characteristics • Number of drivers and voltage requirements • Number of substrates • Switching speed

  27. Switching fabric parameters • A capacity of an optical switch is limited by technology constrains. • To construct switches of greater capacity, many switches are connected between themselves and form a switching fabric. • Many parameters has to be taken into account when designing a switching fabric. Important characteristics used in evaluating optical switching fabrics are: • attenuation and • signal-to-noise ratio (SNR).

  28. Attenuation • Attenuation of light passing through the switching network has several components, but the primary design criterion is the insertion loss in directional couplers.It varies depending on semiconductor technology (generally about 0.5 dB).

  29. Signal-to-noise ratio (SNR) • The SNR is a measure of the optical crosstalk that occurs when two signals interact with each other. These signals can usually interact when they are going trough the directional coupler or waveguide crossover. However,the directional coupler is traditionally regarded as the major reason for the crosstalk.

  30. Crosstalk in the directional coupler Attenuation: IL = PIN/POUT IL [dB] = PIN [dB] – POUT [dB] Crosstalk: Pnoise= kPIN/IL POUT = PIN /IL SNR = 10log10(PIN /Pnoise) = 10log10(1/k) = |X| The value |X| is usually about 20 dB (k = 0.01), and is called the “extinction ratio”

  31. Fiber crossovers • Number of crossovers – fibre crossovers introduce additional signal attenuation and crosstalk.

  32. Cost of switching fabrics • The number of switching elements is a measure of the networks’ cost. • Number of drivers – in some architectures one driver may control more than one switching element.

  33. Combinatorial properties of switching fabrics (1) • The strict-sense nonblocking • There is a possibility to connect any free input with any free output regardless the switching fabric’s state and the way of choosing resources. • The wide-sense nonblocking • There is a possibility to connect any free input with any free output regardless the switching fabric’s state, but we have to use the special control algorithm to choose resources.

  34. Combinatorial properties of switching fabrics (2) • The rearrangeable nonblocking • There is possible to connect any free input and any free output but special control algorithm has to be used and one or more of existing connections may have to be rerouted. • The repackable nonblocking • Similarly like in rearrangeable switching fabrics but rerouting is done after disconnection of one ofexisting connection. • Blocking • Sometimes it is impossible to connect free input with free output because of the current state of the switching fabric.

  35. Hardware complexity vs. control complexity • Strict-sense nonbloncking (SSNB) • Wide-sense nonblocking (WSNB) • Rearrangeable (RRNB) • Repackable (RPNB) • Blocking

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