Recent advances in all-optical signal processing using semiconductor optical amplifiers

National telecommunication networks now routinely use optical fibre for data transmission, with signal processing tasks such as clock recovery, regeneration, demultiplexing and routing being performed electronically. Future very high speed networks with single channel rates of 100 Gbit/s or more require these tasks to be performed with minimal complexity, and one approach is to employ all-optical signal processing using a single high speed gate capable of operating at ~100 Gbit/s. Interest in semiconductor optical amplifiers (SOAs) to act as such a gate were renewed by the development of the TOAD (Terahertz Optical Asymmetric Demultiplexer) and the demonstration of switching rates far in excess of the SOA´s natural recovery rate. Over the past five years very high speed switching and wavelength conversion in various interferometers has been demonstrated. All the interferometers rely primarily on the band-filling nonlinearity for their operation, where the switching pulses transfer electrons from the conduction to valence bands of the SOA via stimulated emission and alter the gain and hence the refractive index. This band filling non-linearity can allow switching operation at very high speeds since only partial recovery of the gain is necessary for a π phase shift to recover on very short time-scales (~lOps). The experiments to be described uses a UNI (Ultrafast Nonlinear Interferometer). This is a derivative of the TOAD, and operates on similar principles