The invention relates to a laser oscillator comprising an amplifying optical fiber (MA) inserted in a resonant cavity so as to act as an active medium, and pumping means (DL, CP) causing a population inversion in said amplifying optical fiber, characterized in that said amplifying optical fiber comprises at least two cores (C1, C2) optically coupled to each other in a common cladding (G), and in that the shapes, sizes, refractive indices and the relative arrangement of said cores are chosen so that super-modes are supported, at least one (SMI) of which super-modes has, in an emission spectral band of said laser oscillator, a normal chromatic dispersion.