Optical waveguide coupling using fabricated waveguide coupling structures

A method for fabricating an integrated optical coupler, the method comprising:

• forming a first waveguide structure supporting a first optical mode coupled to a waveguide coupling structure, the first waveguide structure comprising a first guiding core structure formed on a first cladding structure, and a second cladding structure formed on the first guiding core structure, where the first waveguide structure has a guiding ridge of a first width;
• and
• forming a second waveguide structure supporting a second optical mode coupled to the waveguide coupling structure, the second waveguide structure comprising a second guiding core structure formed on a third cladding structure, and a fourth cladding structure formed on the second guiding core structure, where the second waveguide structure has a guiding ridge of a second width;
• where the waveguide coupling structure comprises
• a transition structure having a third width larger than the first width and larger than the second width,
• a multimode interference structure between the transition structure and the second waveguide structure having a width larger than the first width and smaller than the third width, and
• an electrode covering at least a portion of the transition structure and at least a portion of the first waveguide structure and not covering any portion of the multimode interference structure.