Bend insensitive optical fibers

A optical fiber which is single-mode at 1550 nm comprising a core, an inner cladding and a low index ring, wherein:

• the core comprises silica-based glass, an index of refraction n1, a relative refractive index percent Δ1% relative to pure silica glass, a radius;
• the inner cladding surrounds the core and extends from r1 to a radius r2 such that the inner cladding has a radial thickness of r2-r1, wherein the inner cladding comprises silica-based glass, an index of refraction n2, a relative refractive index percent Δ2% relative to pure silica glass, wherein n1>n2, Δ1%>Δ2% and the difference between Δ1% and Δ2% (Δ1%−Δ2%) is greater than about 0.1%;
• and
• the low index ring surrounds and directly contacts the inner cladding and extends from r2 to a radius r3 such that the low index ring has a radial thickness of r3-r2<20 μm, wherein the low index ring comprises silica-based glass co-doped with boron and fluorine, a third index of refraction n3 and a third relative refractive index percent Δ3% relative to pure silica glass, wherein n2>n3, Δ2%>Δ3% and Δ3% is less than about −0.7%;
• and
• the single-mode optical fiber having a cable cutoff wavelength of less than 1500 nm.