COAXIAL OPTICAL COUPLER AND MANUFACTURING METHOD

PROBLEM TO BE SOLVED: To solve the problems of waveguide phase matching and of coupler length tolerance which are caused when a 'rod' and 'tube' waveguides are used in a single-fiber filter device. SOLUTION: In a method of manufacturing a coaxial optical coupler, a rod-like core member is arranged in a tube, and then, the tube is collapsed on at least a part of the length of the rod-like core member, forming a coaxial coupler equipped with a core waveguide inside a ring waveguide. The core member is composed of at least that part of the core waveguide for which a refractive index is enhanced and at least a part of the tube is made of glass having a smaller refractive index than the part of the core waveguide.