Selective mode excitation in GaAs Multi-Mode Interference MMI Device using Bragg grating

In this paper, the mode coupling between a single-mode waveguide and a Multi-Mode Interference (MMI) waveguide is analyzed under two conditions. First, mode coupling efficiency vs. the distance between two waveguides is calculated while only direct phase matching condition between various modes is in effect. In the second case a Bragg grating is introduced between the waveguides and we show that the two conditions, i.e. Bragg grating assisted phase matching and direct phase matching between different modes, compete to dominate the mode coupling behavior. We show that by adjusting Bragg grating period and waveguide distance, we can pre-dominantly transfer power to any mode of MMI. However power coupling to other MMI modes cannot be entirely eliminated.