Millimeter and submillimeter wave dielectric waveguides are receiving increasing attention for high capacity communication links due to the low transmission loss over a large bandwidth. In this paper, a new single-side multi-mode coupler for efficient excitation of two fundamental and polarization-orthogonal modes of a rectangular dielectric waveguide is pre- sented. This technique doubles the available bandwidth of the waveguide without sacrificing the performance The effect of bending the waveguide is also investigated. Finally, the proposed multi-mode coupler is used to feed a high gain dual-polarized dielectric rod antenna. This also doubles the available wireless capacity of conventional singlepolarized rod antennas.