An optical fiber includes (i) a chlorine doped silica based core having a core alpha (Coreα)≥4, a radius r1, and a maximum refractive index delta Δ1max % and (ii) a cladding surrounding the core. The cladding surrounding the core includes a) a first inner cladding region adjacent to and in contact with the core and having a refractive index delta Δ2, a radius r2, and a minimum refractive index delta Δ2min such that Δ2min