Optical device with vertical waveguide structure

A method of fabricating an optical device having an optical waveguide structure, the method comprising:

• acquiring a semiconductor substrate;
• and
• forming the optical waveguide structure vertically on a major surface of the semiconductor substrate;
• wherein the forming the optical waveguide structure comprises:
• forming a lower optical core;
• forming an intermediate optical cladding on the lower optical core;
• and
• forming an upper optical core on the intermediate optical cladding;
• wherein at least one of the lower and upper optical cores extends from a first end of the optical waveguide structure to a second end thereof;
• wherein the upper optical core is vertically above the lower optical core in a vertical direction perpendicular to the major surface and the intermediate optical cladding separates and is in contact with the optical cores;
• wherein a cladding thickness of the intermediate optical cladding in the vertical direction varies along a length of the optical waveguide structure so that the optical cores are optically coupled in first and second sections of the optical waveguide structure near the respective first and second ends, and are optically uncoupled in a third section between the first and second sections;
• wherein the forming of the intermediate optical cladding comprises forming the intermediate optical cladding with a growth process that selectively grows semiconductor material of the intermediate optical cladding on the lower optical core to vary the cladding thickness from a greater thickness in the third section to a lesser thickness in the first and second sections;
• wherein the optical waveguide structure has a parallel pair of optical waveguides extending from the first section to the second section, a lower optical waveguide of the parallel pair includes the lower optical core and an upper optical waveguide of the parallel pair includes the upper optical core;
• wherein the lower optical waveguide and the upper optical waveguide are vertically stacked with the upper optical waveguide disposed above the lower optical waveguide in the vertical direction such that a vertical plane intersects both the lower optical core and the upper optical core in the first, second, and third sections.