Optical routing with liquid crystal arrays.

This paper outlines two ways in which liquid crystal devices can be used as optical switches in telecommunications networks. This has become a very important area of research as electronic switches are becoming bottleneck in both circuit switched and packet switched networks. These two applications have been highlighted as they require radically different switching techniques, yet liquid crystals an be used in both as the reconfigurable element(1). The first application is in circuit switching, where optical loss, crosstalk and polarisation dependence are all critical parameters, whereas reconfiguration time is not. For this application a reconfigurable hologram written in phase with liquid crystal modulators is used to diffract optical beams in an optically transparent switch fabric. This technique does not suit packet switching as a much faster reconfiguration rate is required and loss and crosstalk are not critical. Hence a shutter based crossbar is used as a packet switch using a liquid crystal which can be reconfigured in 1msec. A hybrid electronic/optical approach is also taken as this allows a much more scalable packet switch to be built.