This paper discusses experimental results of optical characterization of low-loss, robust, high-speed optical link basing on step index (SI) polymeric multimode waveguides. In order to enhance the bandwidth of optical waveguides tuning of numerical aperture by material adoption has been implemented. However, trade-off between tolerance requirements, bandwidth and design rules have to be found. In this paper experimental performance evaluation of SI polymeric waveguides by insertion loss measurement, near- and far-field analysis and optical transmission measurements at high data rates will be investigated. The measurement results will be finally analyzed in order to derive design rules for onboard optical interconnects with multi Gbit/s × m performance.