Optical fiber and manufacturing method of optical fiber

An optical fiber comprising:

• a core to which chlorine is added;
• and
• a clad to which fluorine is added,
• wherein chlorine of 9000 to 13000 ppm is added to the core,
• wherein a relative refractive index difference Δ1 of the core to a pure silica glass is 0.09 to 0.13%,
• wherein a relative refractive index difference Δ2 of the clad to a pure silica glass is −0.36 to −0.17%,
• wherein a difference (Δ1−Δ2) between the relative refractive index difference Δ1 of the core and the relative refractive index difference Δ2 of the clad is larger than or equal to 0.30%,
• wherein a mode field diameter at a wavelength of 1.31 μm is 8.8 to 9.6 μm,
• wherein a stress difference occurring at an interface between the core and the clad is lower than or equal to 60 MPa, and
• wherein a value of a ratio Δ2/Δ1 of the relative refractive index difference Δ2 of the clad to the relative refractive index difference Δ1 of the core is −3.3 to −1.5.