A compact optical system for coupling high-power laser radiation (Nd:YAG) to optical fibers is described. Graded-index optics (GRIN rod) have been used because of their characteristics, such as small dimensions, plane and parallel faces with focus near the exit face, which make them suitable for fiber components. A special coupling unit to connect the microlens with the fiber has been designed, thus obtaining a very compact and stable element. The insertion of a conventional lens at the laser exit has been provided to obtain a better coupling efficiency and to increase misalignment tolerances of the GRIN rod-fiber component. A theoretical approach and an analysis by means of an optical design program, together with details on experimental characterization of the coupling systems with a low-power laser (He-Ne) and high-power laser (Nd:YAG), are reported.