All optical header recognition
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All-Optical Header Recognition. M. Dagenais Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA e-mail: [email protected] Outline. Introduction Description of on-going work on optical header recognition Challenges and Opportunities

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All-Optical Header Recognition

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All optical header recognition

All-Optical Header Recognition

M. Dagenais

Department of Electrical and Computer Engineering,

University of Maryland, College Park, MD 20742, USA

e-mail: [email protected]



  • Introduction

  • Description of on-going work on optical header recognition

  • Challenges and Opportunities

  • Conclusion

Functionality of a packet switch

Functionality of a Packet Switch

  • Routing

    • Reading destination address in packet header

    • Comparing destination address with local look-up table addresses

    • Setting up switch for payload switching

  • Flow Control and Contention Resolution

  • Accurate Synchronization between different modules within the switch

  • Header Regeneration/Reinsertion

  • Our ultimate goals for optical packet header recognition

    Our Ultimate Goals for Optical Packet/Header Recognition

    • Technology scalable from 10 Gb/s to 160 Gb/s

    • 32 bit headers

    • Packets switchable on 1 ns time scale

    • Look-up table at network nodes containing up to 65,000 (2 bytes) addresses

    • Reprogrammable nodes

    Present goals of the project

    Present Goals of the Project

    • All-optical header recognition up to 160 Gb/s

    • 3 out of a 8-bit headers are used for destination address

    • Use successively one bit of header for steering packet in 1 x 2 space switches located at each level of a tree structure

    • Demonstrate header recognition (payload already pre-separated)

    Research goals

    Research Goals

    • Implement packet routing in a network

    • Propose and demonstrate robust all- optical header recognition

    • Demonstrate a tree-based packet switched network operating up to 160Gb/s

    Tree structure for header recognition optical packet switch

    Tree Structure for Header Recognition: Optical Packet Switch

    Slot 1 (clock bit)


    Slot 8 (clock bit)


    Slot 1





    Slot 8







    address bit

    Decision is made at each stage by taking the autocorrelation of header with a properly delayed copy of itself and thresholding the result









    process 1

    address bit
















    address bit



    Non interferometric 1 x 2 space switch

    Control Signals





    Non-Interferometric 1 x 2 Space Switch

    Optical header recognition

    Copy of header

    Optical Header Recognition

    Reading the fifth header bit

    Address Bits

    Control Bits

    Copy of header delayed by 4 bits

    Output of the optical and gate when the 5th bit is 1 for 10gb s data rate

    Output of the optical AND gate when the 5th bit is 1 for 10Gb/s data rate

    Required properties

    Required Properties

    • Must provide considerable speed advantage and ability to simplify the circuit design

    • Switching energies should be similar to those of electronics or potentially less

    • Should have capability for integration

    • Should be scalable with the system bit rate and with transmission protocol

    • Should be polarization independent

    • Can be cascaded in several stages

    Differential mach zehnder gate

    Differential Mach-Zehnder Gate

    • Numerical models show potential for >500 GB/s

    • Achieved up to 336 Gb/s w/ integrated device

    • Achieved ~200 fs switching time at 10 GHz Rep. Rate

    • < 200 fJ switching energy

    • Requires two SOA’s

    • Not limited by carrier lifetime due to dual control pulses (differential mode) but limited by control pulse resolution

    Full header recognition using a single and gate time domain

    Guard time

    Header 2

    Payload 2

    Payload 1

    10 ns

    100 ns

    2 ns

    Packet Schematic

    Full header recognition using a single AND gate: time domain

    Full header recognition using a single and gate wavelength domain

    Full header recognition using a single AND gate: wavelength domain

    Programmable switch

    Mach-Zehnder Gate


    Challenges and opportunities node requirements for 32 bit header recognition at 160 gb s

    Challenges and Opportunities: Node Requirements for 32-bit Header Recognition at 160 Gb/s

    • Optical delay chips:

      • Required delays: 6ps X 32 = 192 ps  6 cm

        Solution: low loss passive waveguides on a chip: silica-on-silicon

  • Optical AND gate

    • Solution: Differential Mach-Zehnder gate switch

  • Serial-to-parallel converter

    • Time domain: combination of time delays, optical AND gate, and fast electronics

    • Wavelength domain: combination of time delays, arrayed-waveguide-gratings (AWG), SOAs, super-continuum fiber, and optical AND gate.

  • Tree network: optical packet switch

    • Integrated chip composed of “passive” (no gain) switches and active switches (with gain)

      Solution: Electro-absorption switches in a tree-structure integrated with SOAs to compensate for losses

  • Switch Programmability

    • Need to combine different packet switch output outcomes into several outputs in a programmable way

  • Packaging requirements

    • Hybrid integration required: delay chip based on silica-on-silicon; optical AND gate and amplification based on InP and electronics based on CMOS

      Solution: Silica-on-silicon optical bench

  • Conclusion


    • Application of ultrafast TDM technologies to photonic packet switching and optical header recognition was presented

    • Photonic header processing has the potential of being scaled up and even beyond 500 Gb/s (1.5 Tb/s demultiplexing already demonstrated).

    • The differential Mach-Zehnder gate is the most promising technology for implementing logic functions, given that it is ultra-fast (500 Gb/s possible) and requires low switching energy (< 200 fJ),

    • The use of a tree architecture allows flexibility. In particular, it can read all the possible headers. In addition, it allows the switch to be programmable.

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