In this paper we outline a simple procedure to obtain an equivalent z-invariant waveguide for a given graded index segmented
waveguide. In particular, the proposed model is shown to predict accurately the modal spot size and the effective indices of the
fundamental and the first higher order modes of a planar parabolic-index segmented waveguide over the entire range of duty
cycles. The result should be useful in simplifying the analysis of general graded index segmented waveguides.