Structures for an edge coupler and methods of fabricating a structure for an edge coupler. The structure comprises an edge coupler including a first waveguide core and a second waveguide core. The first waveguide core is positioned in a vertical direction between the second waveguide core and a substrate. The first waveguide core has a first longitudinal axis, the second waveguide core has a second longitudinal axis, and the second longitudinal axis of the second waveguide core is slanted at an angle relative to the first longitudinal axis of the first waveguide core.