Optical waveguide and method for manufacturing same

An optical waveguide, comprising:

• a core forming layer with a high refractive index;
• and
• a first clad layer with a low refractive index, bonded to a first main surface of the core forming layer,
• wherein the core forming layer is provided in a plane direction with a core portion (A), lateral clad portions (B) each having one side adjacent to a corresponding side of the core portion (A), and high refractive index portions (C) each adjacent to another side of a corresponding one of the lateral clad portions (B),
• the core portion (A) is provided in its plane direction with a central region, and GI regions in each of which a refractive index continuously decreases from the central region toward an interface with the corresponding one of the lateral clad portions (B),
• the lateral clad portions (B) each includes a region having a constant refractive index, and
• the high refractive index portions (C) have broader width than the lateral clad portions (B).