Patent ID: 8428415

Claim:
An optical fiber comprising a silica-based glass portion having an outer diameter of less than about 120 μm, the glass portion comprising a core, an inner cladding, and a low index ring, wherein: the core comprises an index of refraction n 1 , a relative refractive index Δ 1 % relative to the pure silica glass and a radius r 1 ; the inner cladding surrounds the core and extends from r 1 to r 2 such that the inner cladding has a radial thickness of r 2 −r 1 <40 μm and the inner cladding comprises silica based glass, an index of refraction n 2 , a relative refractive index percent Δ 2 % relative to pure silica glass, wherein n 1 >n 2 and the difference between Δ 1 % and Δ 2 % (Δ 1 % - Δ 2 %) is greater than about 0.1%; and the low index ring is an outer most glass portion of the optical fiber surrounding and directly contacting the inner cladding and extending from r 2 to a radius r 3 such that the low index ring has a radial thickness of r 3 −r 2 ≦about 20 μm, wherein the low index ring comprises silica-based glass co-doped with boron and fluorine, a third index of refraction n 3 and a third relative refractive index percent Δ 3 % relative to pure silica glass, wherein n 2 >n 3 ,Δ 2 % >Δ 3 % and Δ 3 % is less than about -0.5%; and a coating surrounding the low index ring, wherein the coating comprises a relative refractive index percent Δ c % relative to pure silica glass and Δ c % >Δ 2 %.