Structures for an optical coupler and methods of fabricating a structure for an optical coupler. A coupling section has a plurality of segments arranged with a pitch, a first waveguide core has a section extending longitudinally over the first plurality of segments of the coupling section, and a second waveguide core has a section extending longitudinally over the coupling section. The section of the second waveguide core laterally spaced from the section of the first waveguide core by a given distance.