An optical fiber includes a core, an inner cladding and a low index ring of silica-based glass. The core comprises silica-based glass, an index of refraction n1, and a relative refractive index percent Δ1% relative to pure silica glass. The inner cladding surrounds the core and comprises an index of refraction n2 and a relative refractive index percent Δ2% relative to pure silica glass, wherein Δ1%>Δ2% and the difference between Δ1% and Δ2% is greater than about 0.1%. The low index ring surrounds the inner cladding and comprises silica glass co-doped with boron and fluorine, a radial thickness of less than about 20 μm, an index of refraction n3 and a third relative refractive index percent change Δ3% relative to pure silica glass, wherein Δ2%>Δ3% and Δ3% is less than about −1.0%.