Optical fiber

An optical fiber comprising:

• a core;
• and
• a clad which is formed so as to surround an outer circumference of the core concentrically with the core, the clad having at least an inner cladding layer adjacent to the outer circumference of the core and an outer cladding layer formed on an outer circumference of the inner cladding layer,
• wherein in a case where a refractive index of the core is Δ1, a maximum refractive index of the core is Δ1max, and an outer circumference radius of the core is r1,
• a refractive index of the inner cladding layer is Δ2, a minimum refractive index of the inner cladding layer is Δ2 min, and an outer circumference radius of the inner cladding layer is r2, and
• a refractive index of the outer cladding layer is Δ3, and an outer circumference radius of the outer cladding layer is r3,
• a relationship of Δ1max>Δ3>Δ2 min is satisfied,
• a relationship of Δ3−Δ2min≦0.08% is satisfied,
• a relationship of r1<r2<r3 is satisfied,
• a relationship of 0.35≦r1/r2≦0.55 is satisfied,
• a cable cut-off wavelength is less than or equal to 1260 nm, and
• an MFD at a wavelength of 1310 nm is 8.6 μm to 9.2 μm.