Analysis of optical directional couplers composed of asymmetrically curved waveguides

The coupled-mode equations describing energy propagation along twin-core single-mode evanescent-wave directional couplers composed of asymmetrically curved cores must be modified from their standard form. By analysing the conformal transformation of a prototypical problem of this type it is shown that a major theoretical assumption of a previously proposed theory and a major consequence of this assumption are in fact correct to a high degree of accuracy. The modified coupled-mode theory results are shown to agree well with those generated using a finite-difference beam propagation method