Dielectric loaded gratings (DLGs) comprised of polymer gratings lying on a thin gold film are used to couple light at telecommunication frequencies in and out of plasmonic waveguides featuring sub-micron cross-sections. The grating couplers are found to be efficient and easy to implement to perform direct fiber-to-fiber telecommunication characterizations of dielectric loaded surface plasmon polariton waveguide (DLSPPW) components. By analyzing the dispersion of the plasmonic Bloch modes supported by DLGs as a function of the period and the filling factor of the gratings, efficient couplers comprised of gratings with a filling factor around 0.5 are designed and fabricated by a simple one-step electron beam lithography process. Typical losses in the range of dB per coupler are obtained for gratings designed to operate at normal and 30 -tilted incidence. The performance of the couplers for normal incidence can be further improved by adding a back-reflecting Bragg mirror. We demonstrate the transmission of a 10 Gbits/s signal along a 75 m-long DLSPPW by using DLG couplers for light injection and extraction. A power penalty below below 0.4 dB on the bit-error-rate has been measured over the entire C-band demonstrating the suitability of DLSPPWs for Wavelength-Division-Multiplexed high bit rate traffic and the efficiency of DLG couplers for fiber-to-fiber characterizations of stand alone DLSPPW components.