Patent ID: 8200057

Claim:
A single mode fiber, comprising: a) a core, b) an inner cladding, c) a depressed cladding, and d) an outer cladding composed of pure silica glass, wherein said core is surrounded in sequence with said inner cladding and said depressed cladding; said core comprises silica glass doped with germanium and fluorine, with a diameter of 8.0-8.8 μm, a relative refractive index difference of 0.35-0.38%, and the contribution of fluoride is −0.09±0.02%; said inner cladding comprises silica glass doped with germanium and fluorine, with a diameter of 18-21 μm and a relative refractive index difference of 0±0.02%; and said depressed cladding comprises silica glass doped with fluorine, with a diameter of 26-36 μm and a relative refractive index difference Δ 32 at the external interface thereof is between −0.22 and −0.35%, and a relative refractive index difference Δ 31 at the internal interface thereof is between −0.20 and −0.35%, and Δ 32 ≦Δ 31 .