All-optical router with PPM header processing in high speed photonic packet switching networks

Le Minh, Hoa (2007) All-optical router with PPM header processing in high speed photonic packet switching networks. Doctoral thesis, Northumbria University.

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Abstract

Rapidly growing internet traffic volume is the major driving force behind the development of optically-transparent and ultra high-capacity photonic packet-switching networks. In such networks, the packet routing decision at each router is made by sequentially correlating an incoming packet header address with addresses in all entries of the router's look-up routing table. The routing task is achieved in the optical domain using all-optical logic gates and optical correlator technologies which have been predominantly replacing the existing low-speed electronic processing devices. Nevertheless when a network is expanded, a larger routing table is required thus exponentially increasing header processing time, which results in the increases in routing latency and complexity. This research aims to significantly reduce the size of the routing table and the number of optical devices required in a router by mapping both the packet header address and the look-up routing table entries into the pulse-position-modulation format, where more than one address could be located in a single entry of a new pulse-position routing table. By simply carrying out a single correlation of the packet header address with pulse- position routing table entries, the router can instantly obtain the routing decision, thus significantly reducing the processing time and neglecting the gain recovery time in existing optical logic gates. The structure of the pulse-position routing table also offers flexibility in the transmission mode including unicast, multicast or broadcast embedded in the optical (physical) layer. In the thesis, a new router based on the pulse-position¬modulation scheme will be introduced. Essential router modules including high on-off contrast-ratio clock extraction, pulse position routing table, header processing and optical switch are proposed and analysed. In addition, the thesis investigates and improves the switching window profile and residual crosstalk performance of the all- optical Mach-Zelmder switches as a building block for the implementation of the above router modules. A number of new variants of Mach-Zehnder-based switches are also introduced to enhance switching inter-output contrast ratio and reduce the complexity in multiple-channel OTDM demultiplexing.

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