Theory of pulse propagation in optical directional couplers

Since the existence of intermodal dispersion or coupling coefficient dispersion in an optical directional coupler was highlighted ten years ago, a number of theoretical studies for the understanding of the significance of this dispersion effect on pulse propagation in a directional coupler under various situations have been reported. This paper provides a review of these studies. Both the normal-mode theory and the coupled-mode theory of the coupler are described. The application of the more popular coupled-mode theory to the study of nonlinear pulse switching, soliton interaction, soliton formation, and active couplers is discussed. Experimental works are also described briefly. © World Scientific Publishing Company.