Multiple-core planar optical waveguides and methods of fabrication and use thereof

A method, comprising:

• forming a lower cladding layer on a waveguide substrate;
• forming a lower waveguide core above the lower cladding layer;
• forming a middle cladding layer on the lower waveguide core and on the lower cladding by a deposition process exhibiting a non-negligible degree of conformality;
• forming an upper waveguide core on the middle cladding above and substantially parallel to the lower waveguide core along overlapping portions of their lengths;
• and
• forming an upper cladding layer on the upper waveguide core and on the middle cladding, wherein:
• refractive indices of the lower, middle, and upper cladding layers are each less than refractive indices of the lower and upper waveguide cores;
• widths of the upper and lower waveguide cores are substantially larger than their respective thicknesses, so that the non-negligible conformality exhibited by the deposition of the middle cladding layer on the lower waveguide core yields a non-planar upper surface of the middle cladding layer that includes a substantially flat portion above the lower waveguide core;
• the upper and lower waveguide cores are arranged so as to jointly support at least one propagating optical waveguide mode along the overlapping portions of their lengths;
• and
• the upper and lower waveguide cores are arranged along the overlapping portions of their lengths so that the supported optical mode is substantially confined bilaterally by the lower and upper waveguide cores, from below by the lower waveguide core, and from above by the upper waveguide core.