Patent ID: 8724954

Claim:
An optical fiber comprising: a core extending in an axial direction while containing an axial center of the fiber, the core having a diameter d 1 of 7.0 μm to 7.4 μm; a first optical cladding layer surrounding the core and having an outside diameter d 2 of 1.67d 1 to 2.5d 1 ; a second optical cladding layer surrounding the first optical cladding layer; and a jacket layer surrounding the second optical cladding layer and containing fluorine having a concentration of 0.06 wt % or higher, wherein a relative refractive index difference Δ 1 of the core with respect to the jacket layer is 0.31% to 0.37%, a relative refractive index difference Δ 2 of the first optical cladding layer with respect to the jacket layer is +0.02% or larger and smaller than Δ 1 , and a relative refractive index difference Δ 3 of the second optical cladding layer with respect to the jacket layer is −0.2% or smaller.