PLANAR OPTICAL WAVEGUIDE ELEMENT

PROBLEM TO BE SOLVED: To provide a waveguide structural body in which a plurality of functional regions are integrated on a single substrate. SOLUTION: In the optimized structural body for a doped silica planar waveguide, efficient coupling between the waveguide and a fiber, the reduction of a manufacturing error of a coupler and a delay element and a small bending radius are allowed by the optimized waveguide. Also, for example, basic elements such as the Dragon router and the Fourier filter are integrated with a high yield by a common manufacturing process. Optimizing is attained by using a core layer thicker than a usual rectangular core waveguide and a width of a core changing every different functional region of an optical circuit. Then, a width of the core is variously changed by using an optical lithography technique in order to optimize waveguide performance while uniformly maintaining a height of the core over the whole substrate.