Optical polarizer with varying waveguide core thickness and methods to form same

An optical polarizer, comprising:

• a first waveguide core over a semiconductor substrate and including a first segment having a vertical thickness that varies along a length of the first segment, and a second segment coupled to the first segment and having a substantially uniform vertical thickness, wherein the first segment and second segment have substantially coplanar bottommost surfaces;
• at least one oxide layer on an upper surface of the first waveguide core;
• and
• a second waveguide core on the at least one oxide layer and vertically aligned with the first waveguide core, wherein the second waveguide core includes a first segment having a vertical thickness that varies along a length of the first segment,
• wherein one of a transverse electric (TE) mode signal and a transverse magnetic (TM) mode signal is coupled between the first waveguide core and the first segment of the second waveguide core.

A method of forming an optical polarizer, the method comprising:

• forming a first waveguide core over a substrate, the first waveguide core including a first segment having a substantially concave upper surface;
• forming a first cladding material over the substrate and on at least an upper surface of the first waveguide core;
• forming a second waveguide core over the first waveguide core and the first cladding material, wherein the second waveguide core includes a first segment having a vertical thickness that varies along a length of the first segment;
• and
• forming a second cladding material on the first cladding material and at least partially surrounding the second waveguide core,
• wherein transfer of one of a transverse electric (TE) mode signal and a transverse magnetic (TM) mode signal from the first waveguide core to the second waveguide core occurs between the first segment of the second waveguide core and the first segment of the first waveguide core.