Structures for managing light polarization on a photonics chip and methods of forming a structure for managing light polarization on a photonics chip. A single-mode waveguiding structure is formed that includes a first waveguide core region and a second waveguide core region positioned above the first waveguide core region. The second waveguide core region includes a first section, a second section connected to the first section, and a third section connected to the second section. The second section has a first width at an intersection with the first section and a second width at an intersection with the third section. The second width is greater than the first width. The first and second waveguide core regions contain materials of different composition.