23-09-2008, 12:56 AM
Definition
With in today's Internet data is transported using wavelength division multiplexed (WDM) optical fiber transmission system that carry 32-80 wavelengths modulated at 2.5gb/s and 10gb/s per wavelength. Today's largest routers and electronic switching systems need to handle close to 1tb/s to redirect incoming data from deployed WDM links. Mean while next generation commercial systems will be capable of single fiber transmission supporting hundreds of wavelength at 10Gb/s and world experiments have demonstrated 10Tb/shutdown transmission.
The ability to direct packets through the network when single fiber transmission capacities approach this magnitude may require electronics to run at rates that outstrip Moor's law. The bandwidth mismatch between fiber transmission systems and electronics router will becomes more complex when we consider that future routers and switches will potentially terminate hundreds of wavelength, and increase in bit rate per wavelength will head out of beyond 40gb/s to 160gb/s. even with significance advances in electronic processor speed, electronics memory access time only improve at the rate of approximately 5% per year, an important data point since memory plays a key role in how packets are buffered and directed through a router.
Additionally opto-electronic interfaces dominate the power dissipations, footprint and cost of these systems, and do not scale well as the port count and bit rate increase. Hence it is not difficult to see that the process of moving a massive number of packets through the multiple layers of electronics in a router can lead to congestion and exceed the performance of electronics and the ability to efficiently handle the dissipated power.
In this article we review the state of art in optical packet switching and more specifically the role optical signal processing plays in performing key functions. It describe how all-optical wavelength converters can be implemented as optical signal processors for packet switching, in terms of their processing functions, wavelength agile steering capabilities, and signal regeneration capabilities. Examples of how wavelength converters based processors can be used to implement asynchronous packet switching functions are reviewed. Two classes of wavelength converters will be touched on: monolithically integrated semiconductor optical amplifiers (SOA) based and nonlinear fiber based.
