Single mode optical fibers with a chlorine doped core and a cladding having a fluorine doped trench region are disclosed. The optical fiber includes a chlorine doped silica core having a core alpha α≥10, a core radius r1 and maximum refractive index delta Δ1max % and a Cl concentration≥0.9 wt %. The optical fiber also has a cladding surrounding the core, the cladding having an inner and an outer cladding. The inner cladding has first and second cladding regions. The optical fiber has mode field diameter at 1310 nm of larger than 9 microns, a cable cutoff wavelength of ≤1260 nm, a zero dispersion wavelength λ0, where 1300 nm≤λ0≤1324 nm, and bend loss at 1550 nm for a 20 mm mandrel of less than 0.5 dB/turn.