Mode conversion and radiation loss caused by refractive-index fluctuations in an asymmetric slab waveguide

The purpose of this paper is to show how much power is converted from an incident TE 0 mode to other guided and radiation modes due to random fluctuations of the refractive index in the core region of an asymmetric slab waveguide. Power conversion is calculated by using a perturbation technique with the assumption that the perturbed field can be expanded in terms of higher guided modes together with radiation modes (air and substrate modes). Curves are presented for mode conversion and radiation loss as a function of thickness of the core region, inhomogeneity scale of the refractive index, and refractive-index difference between the core and substrate. It is shown that the radiated power depends greatly on the refractive-index inhomogeneities, and it exceeds the power of guided mode conversion at short correlation length of the medium fluctuations.