An optical phase-shifting component is used for shifting the phase and modifying the intensity of the light beam injected into the fiber (MMF2). The component is inserted upstream or downstream of, or at an intermediate position in, the fiber. The component uses two mirrors and multiple beam paths between the mirrors. An optical phase-shifting structure (e.g., a reflective phase mask with a structured surface, which can be a mirror) is effective at each reflection of the beam and gradually splits the beam into faster and slower propagation modes. The faster modes are subjected to one or more reflections more than the slower modes and are thereby decelerated. The fast and slow modes are combined again and are then transmitted in a multimode fiber in which the modes have different propagation speeds. The difference in the propagation speeds is thus at least partly compensated.