A design method to achieve wide wavelength-flattened responses in the directional coupler-type optical power splitters

A simple design method to achieve wide flattened bandwidths in the directional coupler-type light power splitters is presented, which is applicable both to the three- and two-guide couplers. Couplers with variable differences along the guide axis in the propagation constant between the waveguides are investigated, and the optimum profiles of the variation of the propagation-constant difference are designed for desired given wavelength responses. Designed examples for the three- and two-port splitting operations in the three-guide coupler and for two-port splitting operations in the two-guide coupler are demonstrated, in which the detuning of the propagation constant is assumed to be given by the electrooptic effect in the LiNbO/sub 3/ used as the substrate.