There is currently considerable research interest in all-optical signal processing for telecommunication applications.
In this paper it is shown that a range of all-optical signal processing functions may be carried out using passive
waveguides and phase-shifting elements as basic building blocks. Two types of multimode interference (MMI) photonic
circuits, based on silicon-on-insulator (SOI) technology, are discussed in detail. In the first type, phase-shifting elements
are added to the ports of MMI couplers. In the second type, the waveguide structure of the MMI coupler itself is
modified to achieve a range of signal processing functions. Designs are verified using 2D and 3D simulations.