An optical fiber includes a core and a cladding which are made from silica glass, allows single mode transmission at a wavelength of 1100 nm, and has a mode field diameter of not less than 4 .mu.m at a wavelength of 1100 nm, and a bending loss of not more than 1 dB per turn with a curvature radius of 1 mm at a wavelength of 1100 nm.