An optical device includes a substrate, a dielectric layer on the substrate, a waveguide within the dielectric layer, a light sensitive component (e.g., a photodetector) in the dielectric layer and coupled to the waveguide, and a plurality of light isolation structures in at least one of the substrate or the dielectric layer and configured to prevent stray light from reaching the light sensitive component. In some embodiments, a light isolation structure in the plurality of light isolation structures includes two opposing sidewalls and a filling material between the two opposing sidewalls. The two opposing sidewalls include an optical isolation layer. The filling material is characterized by a coefficient of thermal expansion (CTE) matching a CTE of at least one of the substrate or the dielectric layer.