A complete physical approach to position the access waveguides of weakly confined multi-mode interference couplers

Abstract The design of an N × N multi-mode interference coupler with weakly guiding condition is considered. Focus is put on the positioning of access waveguides. The best positions are obtained using eigenvectors overlapping requiring only a modal solver leading to a very short computation time as no propagation is required. Beyond its simplicity, it provides a clear physical understanding of the self-image theory when the multi-mode section is weakly guiding. This method computes in addition the tolerance on the access guide positioning. Results are in excellent agreement with those from literature.