PURPOSE: To provide the device which has a high-performance polarizing function or optical fiber transmission or measuring instrument with simple constitution wherein a periodic refractive index distribution is generated in an optical fiber having light induced refraction effect.

CONSTITUTION: A periodic refractive index layer 3 is formed in the core 2 of the single-mode fiber which has light induced refractive index variation effect by projecting many interference fringes, which slant by 45° or nearly 45° to the length direction of the fiber and have optical intervals that are an integral multiple of one wavelength in the length direction of the fiber. Consequently, the (s)-polarized component of monochromatic light passing through this refractive index distribution layer is all radiated out of the fiber by interference effect, but the (p)-polarized component is passed as it is, so the polarization device of simple constitution which has a high degree of polarization is obtained.