A waveguide coupling structure includes: a first section that supports a mode that has an associated first intensity profile that substantially overlaps with an intensity profile associated with a mode supported by a first waveguide portion at a first end of the waveguide coupling structure; a second section that supports a mode that has an associated second intensity profile that substantially overlaps with an intensity profile associated with a mode supported by a second waveguide portion at a second end of the waveguide coupling structure; and a third section, between the first section and the second section, comprising a core structure on a bottom cladding and a supporting structure on the bottom cladding. The supporting structure: (1) overlaps with at least a portion of an intensity profile associated with a guided mode of the third section, and (2) has a shape that is asymmetric with respect to a propagation axis of the guided mode in a plane parallel to a surface of the bottom cladding.