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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

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



optical header recognition
Copy of headerOptical Header Recognition

Reading the fifth header bit

Address Bits

Control Bits

Copy of header delayed by 4 bits

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

  • 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.