Lithium niobate devices in switching and multiplexing

Abstract

Integrated-optics devices in lithium niobate have reached a significant maturity in recent years, and several complex devices have been demonstrated. In addition to performing modulation of light in fibre-optic transmission systems, lithium niobate devices currently offer the only components for photonic switching. Thus lithium niobate devices can be used as spatial, temporal and wavelength switches in high-speed and low-speed systems. In these systems electronic signals control the lithium niobate switches, which process the optical information and which are optically interfaced to optical fibres. Hence I am not concerned with all-optical switching. Examples of applications are multiplexing and demultiplexing of high-speed data streams, bit-by-bit or word-by-word switching in, for example, time-space-time stages or in access couplers in high-speed bus systems. Switch arrays, generally operating at lower speeds (below 1 GHz), can be used for network rearrangement, digital crossconnect, protection switching and generally in situations where the frequency and code transparency of the devices can be used to advantage. The status of lithium niobate devices for switching is reviewed, and performance limitations (including those imposed by polarization properties) and trade-offs are discussed, emphasizing time- and space-switching devices and applications.