Improved Analysis of the Coupling of Optical Waves into Multimode Waveguides Using Overlap Integrals

The optical multimode interconnection technology has become important due to increasing data rates in modern multi-processor systems. In this context, the coupling of optical waves into multimode waveguides has to be analyzed. Ray optical methods are preferred, but are not applicable for all geometries. As full-wave analysis using the mode matching technique is very extensive, we present a simple method based on overlap integrals, to calculate the coupling efficiency of impingingoptical waves. Our approach neglects reflected waves. The corresponding error is corrected by applying a transmission factor, which is that of a plane wave irradiating a dielectric half space. We verify our approach at a planar slab waveguide and a cylindrical fiber, as their mode spectra are well known. The mode matching technique is applied as reference method and the impinging wave is a Gaussian beam with varying angles of incidence and lateral displacements.