In this paper, a semi-analytical method has been proposed for the full-wave modal analysis of optical waveguides. In the first step, the dielectric wa veguide is periodically repeated in one transverse coordinate direction with an arbitrary period. The resulting periodic structure is analyzed for determination of various mode properties. If the period assumes large values, the modes of the periodic structure approach those of the original waveguide. As it will be demonstrated, the full-wave modal analysis of the aforementioned periodic structure can be performed by extraction of natural frequencies of an equivalent network of ideal coupled transmission lines
