<title>Large optical switches</title>

Abstract

Abstract Capacity growth in networks requires optical crossconnect switches that canbe assembled incrementally, probably to large ultimate sizes, preferably using identical submodules of small size. Continued strict- sense nonblocking operation must be ensured during expansion, and expandability should haveminimal impact on the initial cost. Large ultimate sizes mandate multistagearchitectures which impose difficulties in the expansion. We discuss the design of optical switching matrices for >lOOxlOO ports using a new modular multistage architecture that focusses on expandability. Summary Wavelength division transmission can result in very large numbers of optical signals convergingon a single location. In opaque network scenarios [1] the internal operations of central offices will becarried out with all the WDM channels converted to separate signals at a single common wavelength.Electronic switching would be permissible, but at present no suitable switches are available. Provided thatsufficiently large optical switches can be built at suitable cost optical crossconnects would be convenient.Optical switching automatically provides signal transparency, and avoids the need for a second transducerstage. However, a multistage architecture will be required to achieve the very large port count ultimatelynecessary as WDM channel counts rise past one hundred.Three primary issues constrain multistage optical switch architectures in this application. First, thenumber of switching devices traversed must be kept small and identical for all paths to avoid loss and thevariation of loss with path. Secondly, switches must be upgradeable in service to larger numbers of ports.Finally, nonbiocking performance is necessary at all times. Unfortunately, in multistage switching it is very