An optical fiber includes a silica-based glass portion having an outer diameter of less than about 120 μm. The glass portion comprises a core, an inner cladding and a low index ring. The core comprises 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, a radial thickness of less than about 40 μm 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 0.1%. The low index ring surrounds the inner cladding and comprises boron and fluorine, a radial thickness of less than about 20 μm, an index of refraction n3 and a third relative refractive index percent Δ3% relative to pure silica glass, wherein Δ2%>Δ3% and Δ3% is less than −0.5%.