Optical fiber and manufacturing method of optical fiber

A manufacturing method of an optical fiber comprising:

• forming first silica soot by depositing silica microparticles;
• forming a core rod to which chlorine of 9000 to 13000 ppm is added by vitrifying the first silica soot while chlorine is added to the first silica soot;
• forming second silica soot by depositing silica microparticles on the core rod;
• forming a cladding layer to which fluorine is added by vitrifying the second silica soot while fluorine is added to the second silica soot to form a glass base material in which a relative refractive index difference Δ1′ of the core rod to a pure silica glass is 0.09 to 0.13%, a relative refractive index difference Δ2′ of the cladding layer to a pure silica glass is −0.36 to −0.17%, and a difference (Δ1′−Δ2′) between the relative refractive index difference Δ1′ of the core rod and the relative refractive index difference Δ2′ of the cladding layer is larger than or equal to 0.30%, and
• drawing the glass base material at a drawing rate that is higher than or equal to 150 m/min and a drawing tension of 8 to 60 gf.