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A concentrator is a switch in which the number of input fibers is strictly greater than the number of output fibers. Thus, a concentrator drops some input signals and switches each of the remaining signals to output fibers on possibly different wavelengths. If the switching is done in the electronic domain, it is called an electronic concentrator or simply a concentrator. If the switching is performed in all-optical domain, then it is called an all-optical lightpath concentrator or simply lightpath concentrator. With the advancement of wavelength division multiplexing (WDM) technology, there has been an exponential growth in the size of interconnects, their complexity, the number of necessary optical-electrical-optical (O/E/O) converters, and their cost. There is a large mismatch between the capacity and speed of optical transmission compared with electronic transmission which results in a bottleneck of the electronic switches and concentrators in WDM networks. This mismatch motivates design of all-optical switches and lightpath concentrators which can keep data in the optical domain, eliminating the need for costly and inefficient O/E/O conversions. There are several practical deployments of optical networks where it is necessary to switch signals from N fibers to M fibers, where N > M [1]. For example, the function of a hub in metro networks is to collect N lightpaths from several regional hubs and transfer them to M lightpaths in the backbone network. Thus, a hub is a lightpath concentrator [1]. Lightpath concentrators have also been used in the design of all-optical switch architectures [2], [3], [4]. With the advancement of WDM technologies, there has been a need for cost effective WDM interconnects. WDM crossconnects typically have separate stages for space and wavelength switching. These designs are expensive, and the switching costs increase significantly with the increase in the number of lightpaths carried by the fiber. A new paradigm for WDM interconnect design is evolving in which space and wavelength switching is performed simultaneously and seamlessly [2], [3]. This design for WDM crossconnects eliminates the need for separate wavelength conversion stages. In this paper, we present a design of an all-optical lightpath concentrator based on wavelength exchanging optical crossbars (WOC) and WDM Crossbar Switches [2], [3]. The design of an all-optical lightpath concentrator presented in this paper makes use of WOC properties and can similarly achieve a balance between wavelength switching and conversion costs and does not require a separate wavelength conversion stage. |
