US Patent 7526177 Fluorine-doped optical fiber

A single mode optical transmission fiber comprises a depressed core having at least 0.41 weight percent fluorine and an index difference (|Δn1|) with pure silica greater than 1.5×10−3, a depressed cladding having at least 1.2 weight percent fluorine and an index difference (|Δn2|) with pure silica greater than 4.5×10−3 and an index difference (|Δn2|−|Δn1|) with the depressed core greater than or equal to 3×10−3.