A wideband dynamic numerical model of a tapered buried ridge stripe semiconductor optical amplifier is described. The model is based on a carrier density rate equation and a set of travelling-wave equations describing the amplified signal fields and spontaneous emission photon rates. These equations are solved in time and space using a computationally efficient numerical algorithm. The model is used to predict the switching properties of an optical gate. A simple equivalent circuit model of the gate, including package parasitics, is derived that can be used in conventional electrical circuit simulation tools.