Optical fiber

An optical fiber comprising:

• a core;
• an inner cladding surrounding the core;
• and
• an outer cladding surrounding the inner cladding, wherein
• a mean relative refractive index difference Δ1 of the core with respect to pure silica, a mean relative refractive index difference Δ2 of the inner cladding with respect to pure silica, and a mean relative refractive index difference Δ3 of the outer cladding with respect to pure silica satisfy a relationship of Δ1>Δ3≥Δ2,
• a ratio r2/r1 of an inner cladding radius r2 to a core radius r1 is 4.5 or higher and 5.5 or lower,
• a minimum value Δmin of a relative refractive index difference with respect to pure silica is −0.030% or higher and −0.010% or lower,
• a radius rmin at which the relative refractive index difference is the minimum value Δmin satisfies a relationship of r1<rmin<r2, and
• (Δmin−Δ(r1))/(rmin−r1) is −0.002%/μm or lower, where Δ(r1) denotes the relative refractive index difference at the core radius r1.