Reduced scattering-matrix algorithm for high-density plasmonic structures

We describe a method to compute S-matrix interface terms using a selection of eigenmodes. When solving the modal equation, the computation of left and right eigenvectors leads to rectangular eigenmodes matrices. Expressions of S-matrix interface terms are then expressed so as to allow for a significant reduction of the computation cost. The reduction is even further decreased in the case of the B-spline modal method, which deals with sparse matrices. Its convergence is illustrated on a high-density plasmonic structure and compared to a full modal method.