Abstract: The present invention provides methods that can adjust the coupling ratio of an optical waveguide coupler efficiently. The coupling ratio is adjusted by varying the propagation constants ?a and ?b and the coupling coefficient x of the coupling portion by varying the refractive index of the coupling portion by implanting accelerated ions into waveguide cores of the coupling portion, or into the claddings around the cores, of the coupler fabricated. This enables efficient adjustment of the coupling ratio of the optical waveguide coupler.

Abstract: A novel method of depolarizing light propagating through an optical fiber or optical waveguide is disclosed. Ions are implanted from outside of a cladding of an optical fiber to a part of the optical fiber such that the ions will stop in or near the core to depolarize the light propagating through the optical fiber. For example, a silica-based optical fiber with a cladding whose diameter is 125 &mgr;m is irradiated with hydrogen ions accelerated at 2.4 MeV. The implanted hydrogen ions stop in the optical fiber core, thereby depolarizing the light propagating through the optical fiber.

Abstract: The present invention provides fabrication methods of a polarization-maintaining optical waveguide, which forms a polarization-maintaining structure in an optical waveguide (including an optical fiber) easily. The method forms one or more stress-applying parts in a cladding of an optical waveguide utilizing density change induced in the cladding by implanting ions accelerated with high acceleration energy into the cladding. If necessary, changing the acceleration energy of the ion beam, using masks, rotating the optical waveguide against the ion beam, implanting ions from various directions, and/or using various kinds of ions are preferable.

Abstract: The present invention provides methods that can adjust the coupling ratio of an optical waveguide coupler efficiently. The coupling ratio is adjusted by varying the propagation constants &bgr;a and &bgr;b and the coupling coefficient x of the coupling portion by varying the refractive index of the coupling portion by implanting accelerated ions into waveguide cores of the coupling portion, or into the claddings around the cores, of the coupler fabricated. This enables efficient adjustment of the coupling ratio of the optical waveguide coupler.

Abstract: A grating formation method comprises the steps of accelerating ions; causing the accelerated ions to pass through a mask having a shape corresponding to the grating; and implanting the ions, which have passed through the mask, into the core, to form refractive index-variation portions for the grating in the core. The other formation method comprises the steps of accelerating ions, converging an ion beam formed of the accelerated ions, to make a beam diameter identical with or smaller than a width of refractive index-variation portions in a direction of the central axis of the optical waveguide so as to provide a converged ion beam; and intermittently irradiating the converged ion beam to the core, while moving an irradiation position in the direction of the central axis, to implant the ions into the core so as to form the refractive index-variation portions in the core.

Abstract: An optical waveguide grating is formed in an optical waveguide core and/or in an optical waveguide cladding where an electric filed of light propagating in the core is spreading by implanting accelerated ions through a mask to the optical waveguide. The mask has enough thickness to prevent the ions irradiated to the masked parts from reaching the portion where the grating is formed. The acceleration energy of the ions is chosen to make the lateral straggling of the implanted ions in the optical waveguide less than three fourths of the period of the grating, or the acceleration energy is chosen to make all or a part of the implanted ions pass through the portion where the grating is formed.