Design of ridge waveguide couplers with carrier injection using discrete spectral index method

It is shown that the design of ridge waveguide couplers with a uniformly layered refractive index profile can be extended to include the nonuniformity arising within an active layer as a result of carrier injection. This is analysed using the spectral index method combined with a degenerate perturbation approach. The simplicity of this approach makes it possible to solve design problems in which the correct mixing of the fields beneath the ridges is an essential feature of the modelling, and necessary for accuracy of design.