The wideband multimode co-doped optical fiber has a silica core co-doped with GeO2 and Al2O3. The GeO2 concentration is maximum at the fiber centerline and monotonically decreases radially out to the core radius. The Al2O3 concentration is minimum at the centerline and monotonically increases radially out to maximum concentration at the core radius. The cladding has an inner cladding region of relative refractive index Δ2, an intermediate cladding region having a relative refractive index Δ3, and an outer cladding region having a relative refractive index Δ4, wherein Δ3