Abstract: In this paper we present an essentially analytic method for solving four layer planar optical waveguides by using the asymptotic theory which expands the propagation constant into asymptotic series in terms of a small parameter. This method itself is exact and can approach any accuracy desired. However, tha numerical results for a crystal[fiber-optic polarizer show that the second order solution is accurate enough.

Key words: planar optical waveguides, optical waveguides