Efficient and broadband guided wave one-way mode-order conversion with theoretical and numerical analysis

In this article, an efficient method of asymmetric conversion of guided modes is investigated. From a basic excitation consisting of (mainly) the lowest-order mode of the input multimode strip waveguide, we achieve a conversion efficiency of [similar] 60% on average, in the forward propagation case, while the backward propagation is suppressed below 10%. The analytical formulation is based on electromagnetic wave theory with orthogonality relations. Affirmative results between the theoretical and numerical findings based on time and frequency domain analysis are observed. The results of this study will increase the ease of implementing an optical isolator if the breaking time-reversal symmetry could be achieved by nonlinear optics or magneto-optic configurations.