In future telecommunication systems, efforts will be made to exhaust the almost unlimited transmission capacity of optical fibers by applying optical frequency-division-multiplexing (OFDM) techniques. The switching elements of such networks must be able to process OFDM signals as well as time-division-multiplexing (TDM) signals. The extent to which optical signal processing can be brought into use instead of present-day electronic signal processing in such switching elements is examined. Several experiments involving OFDM technologies are described which are intended to underline the significance of those technologies for future telecommunication networks. Various techniques for and experiments on the optical switching of signals in the frequency, space, and time domain are described. Experiments dealing with optical signal regeneration are described.>