Impact of waveguide sidewall roughness on the output uniformity and phase of MMI splitters

In this paper, we develop a model for the effects of waveguide sidewall roughness on the output uniformity and phase of a 3-dB MMI splitter. We achieve this by investigating analytically the effect of sidewall roughness on mode coupling in the MMI section of the splitter using the coupled mode and coupled power equations. Using these equations, the subsequent impact of mode coupling losses on the splitter output uniformity and phase is calculated and results for 1 × 2 and 2 × 2 splitters are presented and compared. Finally, to illustrate the impact of sidewall roughness on the operation of a waveguide device, the response of a Mach Zehnder interferometer comprising 2 × 2 splitters is investigated.