Optical waveguide directional coupler and method for making same

A method for making an optical waveguide directional coupler, comprising:

• providing a base, the base comprising a planar member and a ridge member extending from a side of the planar member, the planar member comprising a top surface, the ridge member comprising a recessed planar portion and a raised portion raised relative to the recessed planar portion and perpendicularly extending from the planar member, the raised portion having an upper surface coplanar with the top surface;
• forming an optical guiding layer on a part of the upper surface and the entire top surface;
• forming a photo-resist layer on the entire optical guide layer;
• forming a Y-shaped photo-resist layer on the optical guiding layer;
• etching the optical guiding layer to obtain a Y-shaped optical guiding layer;
• removing the Y-shaped photo-resist layer from the optical guiding layer;
• and
• heating the base and the Y-shaped optical guiding layer to diffuse the Y-shaped optical guiding layer in the base, thereby forming an optical waveguide directional coupler with a Y-shaped optical waveguide.