Split-step time-domain analysis of optical waveguide devices composed of a directional coupler and gratings

An extended split-step time-domain model for composite coupling structures is reported. Time-dependent coupled-wave equations are solved by splitting of the operators for phase accumulation, forward directional coupling, and reverse Bragg reflection. Through an analysis of an add-drop filter based on a grating-written directional-coupler structure, the proposed modeling method is shown to be an order of magnitude more efficient than the previous methods.