Fluidic waveguides have inward surfaces or areas that face each other, separated by a channel region that can be covered. For example, an integrally formed channel component can include two walls parts and a connecting part, with inward surfaces on the wall parts and, extending between them, a base surface; a covering component's lower surface can also extend between the inward surfaces, bounding the channel region; other fluidic, electrical, and optical components can also be attached. In a stack, the covering component can cover the first channel component, and the lower base surface of each preceding channel component can cover the following channel component. An integrally formed body of light-transmissive material can have a surface that includes a waveguide's inward areas and a base area between them; a covering component can be mounted on areas adjacent the inward areas, providing an enclosed channel region.