We propose in this paper the joint use of WDM and Optical Time Division Multiplexing (OTDM) technologies, which offers an interesting opportunity of splitting the bandwidth of a lightpath into a number of subchannels, using a bit-level Time Division Multiplexing (TDM) scheme directly in the optical domain. The key idea is to split the large bandwidth offered by the optical components by means of a TDM scheme, thereby reusing the same wavelength to transport information from a given source to more than one destination node. D logical links are multiplexed using a bit-level, fixed TDM scheme, and then transmitted from the source node using the same wavelength that is optically routed toward all destination nodes. D represents the TDM degree of multiplexing. We call this TDM lightpath a “Super-Lightpath”. Given a physical and a logical topology, the use of Super-Lightpaths affects only the Routing and Wavelength Assignment (RWA) problem, because the same logical topology can be overlayed by using point-to-point lightpaths carrying one logical link, or using point-to-multipoint Super-Lightpaths, each one carrying more than one logical link, multiplexed by means of TDM. Note that the optimal routing of a Super-Lightpath assumes to find a minimum cost tree rooted in the source node, that reaches every destination in the same Super-Lightpath. This indeed implies the capability of splitting in the optical layer an incoming lightpath into many outgoing lightpaths. In this paper, however, we do not consider this opportunity, and suppose that a lightpath cannot be split in a node, but either terminated or routed to the next node, hence it traces a linear path in the physical topology.

© 2002 Optical Society of America

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