Optical waveguide coupler and method for manufacturing same

A manufacturing method for an optical waveguide coupler, characterized by comprising:

• forming a second core layer on a substrate with a first clad layer in between;
• forming a first core layer having such a distribution of the refractive index that the refractive index is the highest at the middle in the stacking direction so as to cover the second core layer and the first clad layer that is exposed from the second core layer;
• forming a second clad layer on the first core layer;
• forming an end surface from which the layers from the second clad layer to
• the first clad layer are exposed by etching at least the layers from the second clad layer to the first clad layer;
• and
• forming a protrusion in a convex form of the first core layer so that the first core layer protrudes from the first clad layer and the second clad layer through etching under such conditions that the etching rates of the first clad layer and the second clad layer are faster than the etching rate of the first core layer.