Devices that perform all-optical signal processing are of interest in optical computing and optical communications. Two devices that have demonstrated such capabilities are the nonlinear directional coupler (NLDC) and the nonlinear Mach-Zehnder interferometer (NLMZ). In these devices the output intensity depends on the input intensity via the intensity-dependent refractive indices of the substrate and guide region, and the interference between the two channel waveguides. The reported performance of these devices to date has been rather inefficient. To optimize these devices, we have developed a theoretical model of the behavior when the substrate or the guide region is nonlinear, including both the reactive and dissipative terms as well as resonance effects. The software has been written using these models such that the user can vary guide and material parameters and achieve an optimum performance. We discuss and compare various materials and guide parameters that lead to optimized NLDC and NLMZ.