EXPERIMENTAL IMPLEMENTATIONS OF MULTIWAVELENGTH PHOTONIC PACKET SWITCHES - Military Communications Conference, 1995. MILCOM '95, Conference Record, IEEE

Photonic packet switches offer the high speed, data rate and format transparency, and flexibility required by future computer communications and cell-based telecommunications networks. We review experimental progress in Multiwavelength photonic packet switches with an emphasis on all-optical guided wave systems. The term all-optical implies that the data portion of a packet remains in optical format from the source to the destination. While the data remains all-optical, both optical and optoelectronic techniques have been used to process packet routing functions based on extremely simple routing protocols. An overview of the design issues for all-optical photonic packet switching is given and contrasted to electronic packet switch implementations. Low level functions that have been experimentally implemented include routing, contention resolution, synchronization, and header regeneration. System level demonstrations, including centralized photonic switching and distributed all-optical multihop networks, will be reviewed. Introduction In fu tu re f ibe r -op t i c packet switched communications networks, the high transmission link data rates as well as the large number of packets transmitted per second will place severe demands on the aggregate network bandwidth. For packet-based applications (e.g. computer communications, ATMbased telecommunications), packets or cells are individually routed and the switch reconfiguration speed is of prime importance, Although electronic technology can achieve high switching speeds, it is not well matched to the transmission bandwidths of fiber-optic links. Photonic switches provide both the high switching speeds and a transmission bandwidth compatible with the fiber link bandwidth. Perhaps more important, photonic packet switches open the possibility for new network architectures that are transparent to the packet data rate and format, extending the success of point-topoint links to the switched network level. In this paper we review progress towards the realization of photonic packet switches that have the functionality required to build complete switching networks. A complete review of this subject is given in [ 11. Design and implementation issues are very different from their electronic counterparts and new approaches in switch architecture and protocol design are required. Current progress towards experimental implementation of "all-optical'' photonic packet switches is examined. The term all-optical implies that the data portion of a packet is maintained in optical format from the source to the destination. However, the control portion of the packet may or may not be optoelectronically regenerated at each switch depending on the control technique used. optical and optoelectronic approaches to routing control are discussed. Data-Rate and Format Transparency Photonic switch research over the past ten years has focused on how to best utilize the wide available bandwidth to increase performance or fill requirements difficult to perform with electronic switching. One example is the capability of photonic switches in conjunction with optical fibers to maintain data in alloptical format from the source to final destination. This characteristic allows the simultaneous transport of multiple data rates (data-rate transparency) and multiple formats (format transparency). Photonic packet switches are characterized as elastic-buffered or passivebuffered. Here, the term passive-buffered implies that only passive delay lines are used, typically fiber loops. Functionality and Design Principles can be summarized by the five low-level functions: