Optical fiber and method for producing optical fiber

An optical fiber having a central axis, comprising:

• a core made of silica glass and extending along the central axis;
• a cladding made of silica glass, surrounding the core, and extending along the central axis;
• and
• a coating layer made of resin, surrounding the cladding, and extending along the central axis,
• wherein a diameter of the core is 7 μm or more and 14 μm or less,
• wherein an outer diameter of the cladding varies along the central axis,
• wherein a residual stress in a direction along the central axis varies along the central axis, the residual stress being averaged over the core and the cladding in a cross section perpendicular to the central axis,
• wherein a deviation from an average value of the outer diameter and a deviation from an average value of the residual stress have signs opposite to each other,
• wherein the cladding includes an inner cladding surrounding the core and an outer cladding surrounding the inner cladding, and
• wherein a refractive index of the inner cladding is lower than a refractive index of the outer cladding.