FORMATION OF FIBER GRATING

摘要

PROBLEM TO BE SOLVED: To form fiber gratings having large refractive index changes without having double refractiveness by drawing a preform to form a polygonal optical fiber, irradiating the optical fiber with a laser beam from its flank, thereby periodically forming refractive index increasing parts in the longitudinal direction of a core. SOLUTION: A porous glass molding 18 having a glass rod 12 for the core at its center is mechanically cut on four sides in such a manner that the core part exists at the center, by which the rod-shaped porous glass body 20 having a regular quadrangular shape in section is formed. The rod-shaped porous glass body 20 is heat treated to form the optical fiber preform 26 having the core 22 at its center and a clad 24 have the regular square section at its circumference. The optical fiber preform 26 is drawn to produce the optical fiber having the shape resembling the shape of the optical fiber preform 26. The optical fiber is then irradiated with the excimer laser beam at periodic intervals from the flank of the optical fiber by using a phase mask, by which the refractive index increasing parts are periodically formed in the longitudinal direction of the core of the optical fiber.