Lateral confinement in generalized strip-loaded optical waveguides

Abstract

Mode structure in strip-loaded waveguides is studied using an eigenvalue method based on a two-dimensional Fourier analysis. Modified guides where the loading strip is displaced above the core by an additional layer of cladding are considered as a general case. Lateral confinement is found to depend largely on the extent to which the field decays over the strip, and generally worsens as vertical confinement (in the direction perpendicular to the layers of the guide) improves. Conditions that degrade lateral confinement include a large difference in refractive index between core and cladding, a core wide relative to operating wavelength, and large separation between strip and core. Lateral confinement does not vary monotonically with vertical confinement, moreover, but instead may be maximized over a specific range of the guide’s refractive indices.