The invention concerns a multimode optical fiber, with a graded-index core co-doped with at least fluorine F and germanium GeO2 and a refractive index profile with at least two α-values. According to the invention, the concentration of fluorine F at the core center ([F]r=0) is between 0 and 3 wt % and the concentration of fluorine F at the core outer radius ([F]r=a) is between 0.5 wt % and 5.5 wt %, with [F]r=a−[F]r=>0.4 wt %. For wavelengths comprised between 850 nm and 1100 nm, said multimode optical fiber has an overfilled launch bandwidth (OFL-BW) greater than 3500 MHz·km and a calculated effective modal bandwidth (EMBc) greater than 4700 MHz·km over a continuous operating wavelength range greater than 150 nm.