Lightpath Concentration by Circulation An Nxc3x97M lightpath concentrator is an optical component for concentrating lightpaths from N incoming fibers to M outgoing fibers where Nu003eM. In this paper, we propose a novel design of lightpath concentrators that gives significantly better performancecomplexity tradeoff than the existing design. The proposed design uses 2xc3x972 switch elements to form rings which connect the inputs to the outputs. The incoming lightpaths are circulated along these rings in order to reach the available outputs. We demonstrate that: i) the proposed design gives significantly smaller blocking probability than the existing design when both designs have about the same complexity, and ii) the proposed design has significantly smaller complexity than the existing design when both designs have about the same blocking probability.

Wavelength conversion in shortestpath alloptical networks We consider alloptical networks with shortestpath routing that use wavelengthdivision multiplexing and employ wavelength conversion at specific nodes in order to maximize their capacity usage. We present efficient algorithms for deciding whether a placement of wavelength converters allows the network to run at maximum capacity, and for finding an optimal wavelength assignment when such a placement of converters is known. Our algorithms apply to both undirected and directed networks. Furthermore, we show that the problem of finding an optimal placement of converters is MAX SNPhard in both undirected and directed networks. Finally, we give a lineartime algorithm for finding an optimal placement of converters in undirected trianglefree networks, and show that the problem remains (mathcalNP)hard in bidirected trianglefree planar networks.