Patent ID: 6836418
Filing Date: 2004-12-28
Classification: G02B

Abstract:
A slant short-period grating which is obtainable by irradiating light onto an optical fiber having a core and a clad provided on an outer periphery of the core, the core being formed from quartz glass to which has been doped a photosensitive dopant that changes a refractive index of the quartz glass by light irradiation, and the clad having one or two or more layers with at least the layer that is adjacent to the core being a photosensitive layer formed from quartz glass to which has been doped a photosensitive dopant that changes a refractive index of the quartz glass by light irradiation, and thereby a grating portion is formed by changing the refractive index of the photosensitive layer of the clad and the core at a predetermined grating period along a longitudinal direction of the optical fiber by a predetermined slant angle,wherein a diameter of the core is 5 &mgr;m or more; wherein a relative photosensitivity ratio of the core relative to the photosensitive layer of the clad that is adjacent to the core satisfies Formula (1) below: 0.2âˆ’0.1Â·(Vâˆ’1.7)&lE;P&lE;0.1a{0.41âˆ’0.33Â·(Vâˆ’1.7)}â€ƒâ€ƒ(1) in Formula (1), a is the diameter of the core in units of &mgr;m, V is a standardized frequency, and P is the relative photosensitivity ratio of the core relative to the photosensitive layer of the clad that is adjacent to the core; and wherein the slant angle is set to such an angle that loss due to coupling of a waveguide mode with a reflection mode is minimum.