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 n.sub.1, and a relative refractive index percent .DELTA..sub.1% relative to pure silica glass. The inner cladding surrounds the core and comprises an index of refraction n.sub.2 and a relative refractive index percent .DELTA..sub.2% relative to pure silica glass, wherein .DELTA..sub.1%>.DELTA..sub.2% and the difference between .DELTA..sub.1% and .DELTA..sub.2% 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 .mu.m, an index of refraction n.sub.3 and a third relative refractive index percent change .DELTA..sub.3% relative to pure silica glass, wherein .DELTA..sub.2%>.DELTA..sub.3% and .DELTA..sub.3% is less than about -1.0%.