Analysis of step discontinuities in rectangular MMI coupler by beam propagation method

There are many numerical approaches have been developed to analyze general dielectric waveguides. Compared with other numerical techniques, the beam propagation method (BPM) is the most popular and powerful numerical technique for modeling of guided wave photonic devices and most commercial software for such modeling are based on it. To date numerous algorithms for BPM have been proposed and successfully applied to a very wide class of dielectric optical waveguide structures. In this paper, we have analyzed the Multimode interference (MMI) coupler by Beam Propagation Method (BPM) having a step discontinuity between thin planar slab waveguide with wide thick planar slab waveguide. The effect of the waveguide width on the performance of MMI coupler has been analyzed. It has been found that power transmission is asymmetric with waveguide width variation. The relation between the amount of allowed modes with power transmission has been predicted along with pulse propagation through MMI coupler.