Patent ID: 7593612

Claim:
An optical fiber comprising: a center core region; a cladding layer formed around the center core region, the cladding layer having a refractive index lower than a refractive index of the center core region; a tension-absorbing cladding layer formed around the cladding layer, the tension-absorbing cladding layer having a refractive index equal to or higher than the refractive index of the center core region, wherein the center core region has a relative refractive index difference Δ 1 of −0.1% to 0% with respect to a pure silica glass, a chlorine concentration of 0 wt % to 0.10 wt %, and a fluorine concentration of 0.10 wt % to 0.30 wt %, the tension-absorbing cladding layer has a relative refractive index difference Δ 4 of 0% to 0.05% with respect to the pure silica glass and a chlorine concentration of equal to or lower than 0.15 wt %, and a ratio of an outer diameter of the tension-absorbing cladding layer to an outer diameter of the cladding layer is 1.10 to 1.40; and an inner cladding layer formed between the center core region and the cladding layer, the inner cladding layer having a refractive index lower than the refractive index of the cladding layer, wherein a relative refractive index difference Δ 3 of the cladding layer with respect to the center core region is −0.35% to −0.25%, a difference between the relative refractive index difference Δ 3 and a relative refractive index difference Δ 2 of the inner cladding layer with respect to the center core region, Δ 3 −Δ 2 , is 0.05% to 0.20%, and a ratio of an outer diameter of the inner cladding layer to a diameter of the center core region is 3.0 to 4.5.