Structures including a waveguide core and methods of fabricating a structure including a waveguide core. A back-end-of-line interconnect structure includes a cap layer, an interlayer dielectric layer, and one or more metal features embedded in the interlayer dielectric layer. The interlayer dielectric layer is stacked in a vertical direction with the cap layer. The one or more metal features have an overlapping arrangement in a lateral direction with the waveguide core, which is arranged under the back-end-of-line interconnect structure.