Wavelength-flattened directional couplers: A geometrical approach

A new approach to design a wavelength-insensitive optical power splitter is presented. First, a coupled-mode theory is cast in operatorial form. This allows us to solve the equivalent of coupled differential equations as simple limits. The operators are then represented on a generalized Poincaré sphere, and the resulting graphical tool is applied to different structures, giving a clear interpretation of previous results in literature as well as hints on how to find improved solutions.