POLARIZATION-MAINTAINING OPTICAL FIBER

A polarization-maintaining optical fiber of the present invention includes a core, a pair of stress-applying parts provided on both sides of the core, and a cladding surrounding the core and the stress-applying parts, and is used in a wavelength range of 400 to 680 nm. The diameter of the cladding is 125 mum, the diameter of the stress-applying part is 33 to 37 mum, a distance between the pair of stress-applying parts is 8.6 to 15.4 mum, a relative refractive index difference between the core and the cladding is 0.35 to 0.45%, and a cut-off wavelength is less than or equal to 400 nm.